Phases of Matter — Chapter quiz · Physical Science: Matter, Forces & Energy, Grade 8

Explain solids, liquids, gases, and changes of state using particle motion and energy transfer.

Problem 1

A supplied sealed-water model contains 50 g solid, then 30 g solid plus 20 g liquid, then 50 g liquid. The chemical formula remains H₂O throughout. Track mass, identity and arrangement across the three records. Explain what a particle drawing should change and what it should keep.
Answer and explanation

Each record accounts for 50 g water. Melting changes particle arrangement and freedom of movement while retaining H₂O identity. Show a larger liquid fraction through the sequence; do not enlarge individual molecules or turn them into new elements. A drawing with a handful of dots stands for many molecules and is not to scale.

Each record accounts for 50 g water. Melting changes particle arrangement and freedom of movement while retaining H₂O identity. Show a larger liquid fraction through the sequence; do not enlarge individual molecules or turn them into new elements. A drawing with a handful of dots stands for many molecules and is not to scale.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 2

Are the visible white clouds above hot water water vapor itself?
Answer and explanation

The visible cloud is mostly tiny condensed liquid droplets. Gaseous water vapor itself is invisible; the droplets form as warm moist air cools.

The visible cloud is mostly tiny condensed liquid droplets. Gaseous water vapor itself is invisible; the droplets form as warm moist air cools.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 3

Independent chapter check: A labeled pure-water sample has a nearly constant temperature during melting while energy still enters. What changes at particle and whole-sample levels, and which identity stays the same?
Answer and explanation

More of the sample becomes liquid and particle arrangement/freedom of movement changes. Water molecules remain water; a plateau does not mean zero energy input or motionless particles.

Interpret the plateau with the stated phase-change conditions.

Track substance identity separately from arrangement and phase fraction.

More of the sample becomes liquid and particle arrangement/freedom of movement changes. Water molecules remain water; a plateau does not mean zero energy input or motionless particles.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 4

Two supplied water samples at 25 °C have masses 100 g and 400 g. A second pair has equal mass but temperatures 25 and 40 °C. Explain what temperature compares and why equal temperature alone does not imply equal internal energy. Predict the direction of net thermal transfer for the second pair in contact.
Answer and explanation

For the same substance, temperature is related to average particle motion, while internal energy also depends on amount and interactions. The larger 25 °C sample can have greater internal energy despite equal temperature. Net thermal transfer is from the 40 °C sample toward the 25 °C sample under contact conditions, not a flow of a material called cold.

For the same substance, temperature is related to average particle motion, while internal energy also depends on amount and interactions. The larger 25 °C sample can have greater internal energy despite equal temperature. Net thermal transfer is from the 40 °C sample toward the 25 °C sample under contact conditions, not a flow of a material called cold.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 5

Why can equally warm wood and metal feel different?
Answer and explanation

Their thermal transfer properties differ. Metal typically conducts energy away from the skin faster, so sensation does not directly establish a temperature difference.

Their thermal transfer properties differ. Metal typically conducts energy away from the skin faster, so sensation does not directly establish a temperature difference.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 6

Design separate mass and material comparisons using the table. Explain the two trends and specify how a real investigation would verify matched energy input and limit environmental transfers.
Hints

Use the illustrated study titled Compare heating by mass and material. Keep the observations, model and conditions separate.

Answer and explanation

50 versus 100 g water isolates mass in the supplied model and gives rises 4 versus 2 °C. The 50 g water versus 50 g model solid comparison isolates material and gives rises 4 versus 8 °C. Equal input does not impose equal temperature change. Verify input method, starting state, container and surroundings, repeat readings, and label the supplied values rather than claim actual collection.

50 versus 100 g water isolates mass in the supplied model and gives rises 4 versus 2 °C. The 50 g water versus 50 g model solid comparison isolates material and gives rises 4 versus 8 °C. Equal input does not impose equal temperature change. Verify input method, starting state, container and surroundings, repeat readings, and label the supplied values rather than claim actual collection.

Response criteria

  • Choose separately controlled pairs.
  • Explain amount/material response without equating heat with temperature.
  • Specify input, tools, records and uncertainties.

Problem 7

Independent chapter check: Equal masses of the same substance start at 70 and 30 °C and reach equilibrium in the ideal isolated same-phase comparison. Predict the final temperature and explain why changing one mass would change the calculation.
Answer and explanation

50 °C in the stated equal-mass model. A different mass changes the energy amounts associated with each temperature change, so the simple midpoint would not generally apply.

Use equal amounts and the same substance/phase assumptions.

Do not add temperatures or apply the midpoint to unmatched masses.

50 °C in the stated equal-mass model. A different mass changes the energy amounts associated with each temperature change, so the simple midpoint would not generally apply.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 8

Illustrative constant-temperature records give 80 kPa at 60 mL and 120 kPa at 40 mL for one fixed gas sample. Explain the trend and test whether pressure × volume stays constant.
Answer and explanation

80×60=4,800 and 120×40=4,800 kPa·mL. The smaller volume gives greater pressure while the model product stays constant. The gas particles do not shrink; more frequent wall impacts explain the increased pressure. This evidence is conditional on fixed temperature and particle number.

80×60=4,800 and 120×40=4,800 kPa·mL. The smaller volume gives greater pressure while the model product stays constant. The gas particles do not shrink; more frequent wall impacts explain the increased pressure. This evidence is conditional on fixed temperature and particle number.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 9

Why not compare a warm large vessel with a cool small vessel to isolate temperature?
Answer and explanation

Both temperature and volume change. Either can influence pressure, so the difference would not isolate temperature.

Both temperature and volume change. Either can influence pressure, so the difference would not isolate temperature.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 10

Independent chapter check: At fixed temperature and gas amount, the supplied ideal model gives pressure×volume = 180. Predict pressure at volume 3 and at volume 6, then explain why particles do not need to shrink.
Answer and explanation

60 and 30 in the given pressure units. Particle size is unchanged; different spacing and wall-collision patterns explain the pressure change under the stated model.

Divide the supplied constant by each volume.

Hold temperature and amount comparable before attributing the result to compression.

60 and 30 in the given pressure units. Particle size is unchanged; different spacing and wall-collision patterns explain the pressure change under the stated model.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 11

Illustrative records show a cold intact cup with clear outside droplets. An open tray loses 6 g while a covered matched tray loses 1 g in an hour. Explain both observations and identify a limit of the mass comparison.
Answer and explanation

The droplets can be condensed water from surrounding air; the tray loss can be water evaporating into that air. The open tray loses 5 g more under the stated comparison. Covering changes exchange and can also change temperature or airflow, so the result does not isolate every mechanism. Neither observation requires water creation or destruction.

The droplets can be condensed water from surrounding air; the tray loss can be water evaporating into that air. The open tray loses 5 g more under the stated comparison. Covering changes exchange and can also change temperature or airflow, so the result does not isolate every mechanism. Neither observation requires water creation or destruction.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 12

Why is greater loss from a sunny wide tray not proof of an area effect alone?
Answer and explanation

Area, illumination and possibly temperature differ. A comparison changing only intended area is needed to isolate its effect.

Area, illumination and possibly temperature differ. A comparison changing only intended area is needed to isolate its effect.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 13

Independent chapter check: An uncovered sample loses 2 g and a covered sample 0.3 g over the same interval. Explain the supported matter-loss comparison and why these balance readings alone cannot establish the whole energy account.
Answer and explanation

The uncovered sample loses 1.7 g more. Escaping matter can carry energy, but temperature, evaporation energy and other transfer paths need additional evidence for an energy balance.

Compare mass changes for the same boundary and interval.

Keep the matter measurement distinct from an energy measurement.

The uncovered sample loses 1.7 g more. Escaping matter can carry energy, but temperature, evaporation energy and other transfer paths need additional evidence for an energy balance.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 14

Illustrative ice–water data remain near 0 °C for four minutes while a heater supplies 100 J each minute. Account for the 400 J input during the plateau and state an assumption.
Answer and explanation

400 J enters during the four-minute interval. In the simplified model it supports melting and changed particle interactions while the temperature stays approximately constant. It is not missing energy. Some real input can also reach the container or surroundings, so attributing all 400 J to the sample requires an idealized boundary and negligible losses.

400 J enters during the four-minute interval. In the simplified model it supports melting and changed particle interactions while the temperature stays approximately constant. It is not missing energy. Some real input can also reach the container or surroundings, so attributing all 400 J to the sample requires an idealized boundary and negligible losses.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 15

Can a temperature of 0 °C alone tell us the fraction of liquid water?
Answer and explanation

No. Pure ice, a solid–liquid mixture or liquid at that temperature may be possible under the stated conditions; additional state evidence is needed.

No. Pure ice, a solid–liquid mixture or liquid at that temperature may be possible under the stated conditions; additional state evidence is needed.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 16

Independent chapter check: A supplied heating curve is level near 12 °C while the sample’s liquid fraction increases. Can you call the material pure water at ordinary pressure solely from the plateau? Explain what the record supports.
Answer and explanation

No. A phase-change interpretation is supported by the growing liquid fraction, but 12 °C is not ordinary-pressure pure water’s melting point. Composition, pressure and other properties need to be checked.

Use both temperature and phase evidence.

Do not treat every plateau as water melting at a universal temperature.

No. A phase-change interpretation is supported by the growing liquid fraction, but 12 °C is not ordinary-pressure pure water’s melting point. Composition, pressure and other properties need to be checked.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

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