Solid, liquid, gas states and changes of state

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Compare the shape and volume of solids and liquids
Use a particle model without treating it as a photograph

Vocabulary: solid · liquid · volume · particle model · flow

Retrieve previous learning

What is volume?

Check: Volume is the space occupied by a substance or object, measured in units such as cubic centimetres or millilitres.

Learn the concept

A solid usually keeps its own shape and has a volume that changes little when moved between containers. A wooden block retains its outline; a piece of plasticine can be deformed when force is applied, so 'fixed shape' is a useful description under ordinary handling rather than a claim that no solid can change shape. Compare the same sample before and after transferring it, keeping quantity and conditions similar.

A liquid flows and takes the shape of the part of its container that it occupies. It does not automatically fill every part of a container: water in a tall glass occupies the bottom. Its volume stays approximately the same when poured into a wider vessel, provided none spills or evaporates. The liquid surface is often level when the container is stationary, but movement and wetting of the walls can affect what is seen.

In a simple particle model, solid particles remain close and vibrate about positions, while liquid particles remain close but can move past one another. The model explains why a liquid flows although it is difficult to compress appreciably under ordinary classroom conditions. The drawn circles are symbols and are not photographs of atoms or molecules. The model does not show every attractive force or the precise particle arrangement of each substance.

Do not classify a substance merely by whether a heap can be poured. Sand can be poured because separate solid grains move past one another; each grain retains its own shape. Compare one grain with the bulk heap. Use observations of a single continuous sample, particle reasoning and stated conditions before naming a state. Matter may have more complex behaviour than these introductory categories.

Worked model

Observe a block moved between two containers; record that its outline remains recognisable.
Observe an equal amount of water transferred to a wider vessel; record its new outline and similar volume if none is lost.
Represent solid particles as close together and vibrating, and liquid particles as close together but able to change neighbours.
Explain a pouring heap of sand as moving solid grains, not a liquid made by a change of state.

Guided practice

Why does water change outline when poured while its volume is approximately conserved?

Hint: Separate shape from amount and assume no spill.

Check the guided answer

The liquid flows to occupy the bottom of the new vessel, changing outline. The same amount remains if none is lost, so its volume is approximately conserved.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“Anything that can be poured is a liquid.”

Correction: A heap of separate solid grains can pour; classify the grains and explain their movement.

Extend and reflect

What further evidence would help classify a soft material that slowly changes shape?

Guidance: State observation timescale, applied force and temperature; avoid forcing every material into a simple rule from one observation.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Chemistry and Materials Science

This lesson practises: Compare the shape and volume of solids and liquids. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Chemistry and Materials Science. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Chemistry and particle ideas · original lesson pack

DASKEREL beta · internal AI review pending

Melting explained by the particle model

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Describe melting as a physical change
Explain particle motion and arrangement while preserving identity

Vocabulary: melting · solid · liquid · physical change · thermal energy

Retrieve previous learning

How do particles in a solid and a liquid differ in motion?

Check: Solid particles vibrate about positions; liquid particles remain close but move past one another.

Learn the concept

Melting is the change from solid to liquid when energy is transferred to a substance under suitable conditions. A frozen water sample becomes liquid water; its chemical identity remains H₂O. In a closed system the total matter is conserved. An observed fall in mass of an open dish would prompt a check for material lost by spilling or evaporation rather than proof that particles vanished during melting.

In the introductory model, particles in a solid vibrate about relatively stable positions. Energy transferred to the substance can increase their motion and, at the change of state, allow them to move past one another while remaining close. The particles themselves do not turn from 'solid particles' into a new kind of 'liquid particle'. State names describe how the sample behaves and how its particles are arranged and move.

A particle drawing may use ordered circles for a solid and closely packed, less ordered circles for a liquid. The gaps in a drawing are exaggerated to make ideas visible; it cannot predict a substance's exact volume change. Not every substance changes volume by the same amount. Ice and liquid water need particular care because water does not fit every simple 'particles always get farther apart on melting' story.

Melting does not automatically mean the temperature rises continuously. At a near-constant melting temperature for a pure substance under specified conditions, incoming energy changes particle arrangement and interactions while the sample changes state. Real measurements can show ranges or small variations. A written model should distinguish energy transfer, particle motion, arrangement and chemical identity rather than claiming that heating creates matter.

Worked model

Name the initial sample as solid H₂O and the final sample as liquid H₂O.
Draw close particles vibrating about positions for the solid; draw close particles able to exchange neighbours for the liquid.
State that energy is transferred to the sample and changes its arrangement during melting.
Check conservation: in a closed system the same H₂O particles remain; the state changes, not the substance.

Guided practice

Does an ice particle itself melt into a different chemical particle?

Hint: Compare chemical formula before and after.

Check the guided answer

No. Ice and liquid water both contain H₂O molecules. The arrangement and movement of those molecules change during melting.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“The particles themselves become liquid or disappear when a solid melts.”

Correction: The same particles remain; the sample changes state as their arrangement and movement change.

Extend and reflect

Why should a general particle diagram not predict whether ice or liquid water is denser?

Guidance: It omits molecular interactions and water's distinctive structure; use measured evidence for this comparison.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Chemistry and Materials Science

This lesson practises: Describe melting as a physical change. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Chemistry and Materials Science. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Working scientifically · original lesson pack

DASKEREL beta · internal AI review pending

Bunsen burners: supervised practical reasoning

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Identify why heat-work requires controls
Interpret a teacher-provided heating record without claiming practical competence

Vocabulary: Bunsen burner · hazard · risk assessment · supervision · temperature record

Retrieve previous learning

What changes when ice melts?

Check: The arrangement and movement of H₂O particles change while the chemical substance remains water.

Learn the concept

A Bunsen burner is laboratory equipment that can produce a flame for teacher-planned heating. Flame, hot apparatus, heated liquids and nearby materials are hazards. A burner body or base and surrounding equipment must never be assumed cool after use. This written lesson identifies reasons for safety controls; it is not a set of operating instructions, and reading it does not establish that a pupil can use a burner safely.

Any practical burner use requires a trained teacher's direct supervision, a school laboratory risk assessment and approved school equipment and procedures. The teacher determines whether the activity is appropriate, the protective equipment and the setup. Pupils must follow their teacher's instructions and report concerns. A home experiment or unsupervised attempt is not part of this course. Where a practical cannot be provided, a teacher demonstration or a supplied record can support the scientific reasoning.

A scientist separates observation from inference. In a supplied heating graph, time belongs on the horizontal axis and measured temperature on the vertical axis with units. A rising temperature suggests the sample's measured temperature increased during that interval. A flatter part may be consistent with a change of state, but its cause should be checked against observations and the substance involved; a single shape does not prove a melting point or purity.

Measurements have limitations. A temperature probe can lag behind a changing sample; readings depend on probe placement, calibration and timing. A reported value should carry units and be interpreted at the stated conditions. A learner can practise choosing axes, spotting hazards from a scenario and suggesting what evidence to record. Only direct observed practice under a trained teacher's assessment could establish hands-on competence.

Worked model

Read a teacher-supplied scenario of a heating activity; identify flame, hot vessel and hot liquid as potential hazards.
State that a trained teacher, school risk assessment, school equipment and direct supervision govern any practical use.
Read a fictional graph labelled time (minutes) and temperature (°C); describe an interval where temperature rises.
Interpret a flatter interval cautiously as possible state change evidence, then name an observation needed to check it.

Guided practice

A pupil has read this page. Can they now claim independent Bunsen competence?

Hint: Distinguish written reasoning from observed practical performance.

Check the guided answer

No. The page supports written safety and data reasoning only. Practical competence requires teacher-supervised use and direct assessment with school procedures and equipment.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“A written Bunsen quiz gives permission to use a burner alone.”

Correction: Written work cannot confer practical competence or replace trained teacher supervision, school equipment and risk assessment.

Extend and reflect

How might probe placement affect a temperature graph?

Guidance: Explain that different parts of a sample may warm at different rates; seek teacher-approved repeated measurements rather than asserting a plateau is exact.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Physical Sciences

This lesson practises: Identify why heat-work requires controls. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Physical Sciences. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Data Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Chemistry and particle ideas · original lesson pack

DASKEREL beta · internal AI review pending

Melting and freezing points from evidence

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Relate melting and freezing for a pure substance under specified conditions
Interpret temperature records with uncertainty

Vocabulary: melting point · freezing point · pure substance · temperature plateau · measurement uncertainty

Retrieve previous learning

Why can a near-flat heating graph require more evidence?

Check: It may be consistent with a change of state, but observation, substance identity and measurement conditions are needed to justify that interpretation.

Learn the concept

Melting changes a solid to a liquid; freezing changes a liquid to a solid. For a pure substance at a specified pressure, the equilibrium melting and freezing temperature is the same. For water at normal atmospheric pressure, a classroom reference value is approximately 0 °C. This is a condition-dependent reference, not an exact prediction for every reading or every sample. Mixtures and impurities can show different behaviour.

A heating record may level near the melting point while solid and liquid coexist. During the change, transferred energy alters particle arrangement and interactions rather than simply raising the sample's temperature. Cooling can show a near-flat section while freezing occurs, as energy leaves. Neither graph proves that individual particles have changed chemical identity; water remains H₂O in both states.

Measurements can show a range rather than a perfect horizontal line. Probe response, sampling interval, uneven heating and impurities can affect readings. Supercooling can cause a cooling sample to drop below its usual freezing temperature before freezing starts. Thus a measured low point on one graph is not automatically a new equilibrium freezing point. Record evidence and uncertainty rather than rounding every graph into an ideal textbook line.

To compare records fairly, name the substance, whether it is reasonably pure, the pressure or atmospheric conditions, and what was observed. Read values with units from axes. A flat interval can support a state-change interpretation if independent observation agrees, but cannot by itself prove purity. Practical heating or cooling, if carried out, remains subject to a trained teacher's school risk assessment and equipment decisions.

Worked model

Read a supplied graph for pure water at normal atmospheric pressure; note an observed near-flat interval around 0 °C.
Associate the interval with possible coexistence of ice and liquid water, using teacher-provided observations.
Read a cooling record and distinguish a near-plateau from a brief lower point caused by possible supercooling.
Conclude that melting and freezing points match in equilibrium under specified conditions, while real readings can vary.

Guided practice

Does a cooling graph's brief dip below 0 °C prove water's freezing point changed?

Hint: Think of supercooling and measurement conditions.

Check the guided answer

No. A brief dip may occur before freezing begins or reflect measurement limitations. Equilibrium freezing point and one observed minimum are different claims.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“Every measured freezing graph must stop exactly at the textbook temperature.”

Correction: Textbook values describe equilibrium under conditions; real data can vary and supercooling may occur.

Extend and reflect

How would you distinguish a plateau from a measurement artefact?

Guidance: Seek direct state observations, calibration information and repeated teacher-controlled measurements; report uncertainty.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Chemistry and Materials Science

This lesson practises: Relate melting and freezing for a pure substance under specified conditions. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Chemistry and Materials Science. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Chemistry and particle ideas · original lesson pack

DASKEREL beta · internal AI review pending

Gas particles, volume and pressure

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Explain why a gas fills its container
Relate gas pressure to particle collisions with a container

Vocabulary: gas · particle model · pressure · collision · compressible

Retrieve previous learning

What remains the same when water melts?

Check: The substance remains H₂O and matter is conserved in a closed system, although particle arrangement and movement change.

Learn the concept

A gas has no fixed shape or volume of its own. It spreads through the available space in a container; unlike a liquid in a glass, it can occupy the whole container. The amount of gas still matters: an empty-looking balloon can contain gas with measurable mass. The word 'gas' describes a state of matter, not a substance with no particles. Different gases have different chemical identities and properties.

In a simple model, gas particles are far apart relative to their size and move in varied directions, colliding with one another and the container walls. Their collisions with the walls contribute to gas pressure. The particle diagram's empty spaces are a schematic representation, not a scale drawing. The gas particles do not expand to fill the container; they move through the available volume. The same molecules can remain present as a sample changes state.

A gas is more compressible than a typical liquid because the particles have much more space between them in this introductory model. If a closed syringe of air is pushed in by a teacher in a supervised demonstration, the gas volume may decrease without the particles themselves becoming smaller. Pressure may rise as wall collisions change, but interpreting the precise change requires controlling temperature and the amount of gas. No pupil should improvise pressure experiments with sealed heated containers.

Compare gas, liquid and solid samples of the same substance under stated conditions. A water vapour sample consists of H₂O molecules, just as liquid water and ice do; the typical spacing and motion differ. Avoid claiming every gas is always hotter or contains more energy than every liquid, because substances and conditions vary. Use the model to explain observations, and say which details it leaves out, such as molecular forces and exact collision paths.

Worked model

Read a supplied diagram showing a gas sample in a sealed vessel and identify particles throughout its available space.
Represent the particles as small symbols far apart relative to their size and moving in varied directions.
Link collisions with the vessel walls to pressure without claiming the particles swell.
Compare a smaller vessel at controlled conditions and explain why the gas can be compressed more than a liquid.

Guided practice

Why does a gas fill a container without individual particles growing?

Hint: Consider where particles can travel.

Check the guided answer

Gas particles move through the available space and spread out. Each particle remains the same kind of particle; the distribution of particles changes, not their size.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“Gas particles enlarge when a gas fills a larger vessel.”

Correction: Particles spread through more available volume; the particles themselves do not enlarge.

Extend and reflect

What conditions would you hold constant when comparing gas pressure at two volumes?

Guidance: State the amount of gas and temperature, and explain that these controls are needed before attributing pressure differences to volume.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Chemistry and Materials Science

This lesson practises: Explain why a gas fills its container. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Chemistry and Materials Science. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Chemistry and particle ideas · original lesson pack

DASKEREL beta · internal AI review pending

Boiling, condensation and invisible water vapour

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Compare boiling and condensation using the particle model
Distinguish invisible water vapour from visible droplets

Vocabulary: boiling · condensation · water vapour · bubble · boiling point

Retrieve previous learning

What causes gas pressure in the particle model?

Check: Moving gas particles collide with container walls; the resulting forces across the wall area contribute to pressure.

Learn the concept

Boiling is a liquid-to-gas change in which vapour bubbles can form within the liquid, not only at its surface. For pure water at normal atmospheric pressure, the familiar boiling point is approximately 100 °C. The value depends on external pressure, so it should not be stated as universal. A teacher-supplied graph may show a near-constant temperature during boiling while transferred energy changes the state. A real record may not be perfectly flat.

Condensation is a gas-to-liquid change. When water vapour loses enough energy under suitable conditions, H₂O molecules come closer and liquid droplets form. The H₂O identity remains the same. Condensation can appear on a cool surface; the liquid did not emerge from inside the surface. A cold window may collect droplets from water vapour in surrounding air. The model explains the change in arrangement without creating or destroying matter.

Water vapour itself is an invisible gas. A visible white cloud above warm water or near a spout mainly consists of tiny liquid droplets formed after vapour cools. Calling that visible cloud 'steam' is common everyday language, but the distinction matters in science. A gas may also be invisible without being safe; do not use appearance to judge the hazard of hot vapour or heated equipment.

No learner should boil liquids or handle hot vessels from this text. Any practical observation requires a trained teacher, a school risk assessment, approved equipment and direct supervision. Written preparation can use labelled diagrams, teacher-provided video or temperature records. It cannot prove competence with hot apparatus. When reading evidence, identify pressure and substance, avoid assuming every bubble in a warming liquid is pure water vapour, and distinguish observation from interpretation.

Worked model

Read a teacher-supplied water heating account at normal atmospheric pressure and identify bubbles forming within the boiling liquid.
Qualify the approximate 100 °C reference with pressure and measurement conditions.
Trace H₂O molecules from liquid to invisible gas and back to liquid droplets during condensation.
Identify a visible white cloud as condensed droplets rather than the invisible water vapour itself.

Guided practice

Why are droplets on the outside of a cold glass evidence of condensation?

Hint: Think about water vapour in surrounding air.

Check the guided answer

Water vapour in the air can lose energy at the cold surface and form liquid droplets. The water does not need to pass through the glass wall.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“The visible white cloud is water vapour gas.”

Correction: Water vapour is invisible; the visible cloud is mainly condensed liquid droplets.

Extend and reflect

Why can water boil at a different temperature on a high mountain?

Guidance: Atmospheric pressure changes with altitude, and boiling temperature depends on pressure; avoid claiming the H₂O molecules become a new substance.

Where this lesson could lead · Combined Science: Trilogy GCSE → Daskerel Chemistry and Materials Science

This lesson practises: Compare boiling and condensation using the particle model. Scientific explanation, measurement and evidence support later laboratory, technical and quality work.

Next school subject: Combined Science: Trilogy GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Chemistry and Materials Science. Explore further study and build evidence from practical work.
Later credential exploration: No subject-specific professional credential is mapped from this lesson. Explore the credential catalogue after choosing a later specialism.
Example career direction: Laboratory Analyst. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 7 · Chemistry and particle ideas · original lesson pack

DASKEREL beta · internal AI review pending

Energy, evaporation and changes of state

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Distinguish evaporation from boiling
Explain energy and matter in state changes and open systems

Vocabulary: evaporation · boiling · energy transfer · surface · closed system

Retrieve previous learning

What is the difference between invisible water vapour and a visible white cloud?

Check: Water vapour is an invisible gas; the white cloud is mainly tiny condensed liquid droplets.

Learn the concept

Evaporation changes liquid to gas at the surface and can occur below the liquid's boiling point. Some surface particles have enough energy to leave the liquid. Boiling differs because vapour bubbles form throughout the liquid once conditions for boiling are reached. Do not say evaporation happens only when a liquid is heated to its boiling point. The rate depends on conditions including temperature, exposed area, air movement and humidity, rather than one universal number.

When higher-energy particles leave the surface, the remaining liquid can cool if energy is not replaced as quickly. This explains why an evaporating wet surface may feel cooler, though the effect depends on surroundings and energy transfer. During boiling at a near-constant temperature for a pure substance under specified pressure, energy input is involved in changing particle arrangement and interactions. A flat graph does not mean no energy enters the sample.

Melting and evaporation both require energy transfer to overcome interactions enough for a different state; freezing and condensation transfer energy out to surroundings. These statements describe the overall process, not a claim that all particles have identical energy. Keep the same substance and stated conditions when comparing states. The H₂O molecules in water remain H₂O during evaporation or condensation; chemical identity does not change in these physical processes.

An open shallow dish may lose measurable liquid mass as water vapour leaves the dish and enters the air. Matter has moved beyond the measured dish; it has not been destroyed. In a sufficiently closed system, the total mass including liquid and vapour remains conserved. A written mass-accounting diagram should define its boundary before concluding where matter went. Do not heat sealed containers or improvise evaporation experiments; practical work requires teacher supervision and a school risk assessment.

Worked model

Read a supplied observation of a puddle shrinking below water's boiling point and identify surface evaporation.
Contrast this with a teacher-described boiling sample where vapour bubbles form within the liquid.
Draw a system boundary around an open dish, then extend it to include the surrounding vapour when accounting for mass.
Explain possible cooling as energetic particles leave, while noting energy can also enter from surroundings.

Guided practice

A dish loses 2 g of water after standing open. Has 2 g of matter been destroyed?

Hint: Define the system boundary.

Check the guided answer

No. Some water has evaporated into the surrounding air. The dish alone loses mass, but the matter remains in a larger system that includes the vapour.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Find and correct a misconception

“A liquid evaporates only when it reaches its boiling point, and lost mass is destroyed.”

Correction: Surface evaporation can occur below boiling; material can leave an open container as vapour while matter remains conserved in a larger system.

Extend and reflect

How might humidity affect evaporation from two identical open dishes?

Guidance: Propose a fair comparison with temperature, area and air movement controlled; describe an expected trend as a hypothesis rather than a guaranteed measurement.