Year 7 Science · Unit 2 · Lesson 2
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Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. The particles in a solid do not move at all.
Correct it:
2. The spaces between the particles of a gas are filled with air.
Correct it:
3. The bubbles in boiling water are made of water vapour.
Correct it:
4. Heating a substance makes its particles move faster.
Correct it:
5. Water can only evaporate when it reaches 100 °C.
Correct it:
1. Name the three state changes in which a substance gives out energy.
Order the steps: how the smell of pizza reaches you
Number the events from 1 (first) to 4 (last).
| Order (1–4) | Event |
|---|---|
| Bouncing off air particles, they spread from the crowded kitchen into rooms where there are fewer of them. | |
| A few smell particles reach the receptors in your nose, and you smell pizza. | |
| The gas particles move fast in all directions, through the empty spaces between the air particles. | |
| The hot pizza gives off particles of food chemicals as a gas. |
Cause and effect: a railway track on a hot day
Fill the two empty boxes. Each box is caused by the one before it, and row 2 carries on from the end of row 1.
2. A balloon is blown up indoors at 22 °C, then taken outside on a 5 °C winter morning. Predict what happens to the balloon, and explain using the particle model.
Read the data: how much does a rail grow?
Scenario
A 100 m steel rail is laid on a cool morning at 10 °C. Engineers work out how much longer it gets as the sun warms it.
| Temperature of the rail (°C) | 10 | 20 | 30 | 40 | 50 |
|---|---|---|---|---|---|
| Increase in length (mm) | 0 | 12 | 24 | 36 | 48 |
Source: values calculated for this worksheet from how much steel expands when heated.
3. Plot the data in Table 1 as a line graph. Label both axes with units, and give the graph a title.
4. Describe the trend in your graph. Use it to predict the increase in length at 35 °C.
5. Jack says: “A puddle can’t dry on a cold day, because water only turns into a gas at 100 °C.” Use the particle model to explain why Jack is wrong. Compare evaporation with boiling in your answer.
True or false
1. False: solid particles vibrate on the spot. 2. False: the spaces between particles are empty, not filled with air. 3. True. 4. True. 5. False: water evaporates from its surface at any temperature; it boils at 100 °C.
Question 1
Freezing, condensation, deposition (two correct = 1; all three = 2). [2 marks]
Order the steps: how the smell of pizza reaches you
Reading down the table as printed, the correct step numbers are 3, 4, 2, 1. In order: the pizza gives off smell particles as a gas; they move fast through the empty spaces; bouncing off air particles, they spread into other rooms; a few reach your nose.
Cause and effect: a railway track on a hot day
Box 1: the steel particles gain energy and vibrate faster (1). Box 2: the vibrating particles take up more space, pushing a little further apart (1). [2 marks]
Question 2
The balloon shrinks (1). The air particles inside lose energy and slow down, so they take up less space (1). [2 marks]
Read the data: how much does a rail grow?
3. Axes labelled with units (temperature in °C on x, increase in mm on y), even scales (1); all five points plotted correctly (1); straight line through the points and a title (1). [3 marks]
4. As the temperature rises, the length increases steadily, by 12 mm for every 10 °C (1). At 35 °C: 30 mm (accept 29–31 mm read from the line) (1). [2 marks]
Question 5
Marking guide: 1 Jack is wrong; 1 evaporation: only at the surface, at any temperature; 1 boiling: right through the liquid, only at the boiling point (100 °C for water); 1 surface particles that gain enough energy break free and escape as a gas; 1 everyday evidence (washing dries on cool days). [5 marks]
Model answer: Jack is wrong. Evaporation happens only at the surface, at any temperature: surface particles that gain enough energy break away and escape as water vapour, so a puddle, like washing, dries on a cold day. Boiling happens right through the liquid, only at the boiling point (100 °C for water), so bubbles form at the bottom of a saucepan.
Common error: treating evaporation and boiling as the same thing.