Answers to end-of-chapter questions
Chapter 9
1 See Figure 9.2.
11 a Molecules of ethanol leave the surface
of the liquid
so that its mass decreases.
2 See Figure 9.5.
3 a energy
b The more energetic molecules of ethanol
are more likely to leave the liquid,
so the average energy of the molecules
remaining decreases.
Hence its temperature decreases.
b temperature
4 a evaporation
b faster-moving or more energetic; decrease or
fall/drop
5 a smoke particles
b molecules of the air
b The pressure will decrease.
[1]
b In the liquid, forces between the
particles hold them together.
If it is to become a gas, energy must be
supplied to overcome these forces and
separate the particles.
c quickly
7 a pressure × volume = constant
[1]
9 a solid
b The particles are well separated and
can move about within the volume
of their container,
colliding with its walls and with
each other.
10 a particles of smoke
b The smoke particles are moving
because the particles of the air are
continually colliding with them,
changing their speed and direction
of motion.
© Cambridge University Press 2014 IGCSE Physics
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15
a
Solid
Liquid
[1]
[1]
[1]
120 000 × 20 = 160 000 × V2
V2 = 15 m3
b
[1]
[1]
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c liquid
[1]
p1V1 = p2V2
14
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b quickly
b solid
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12 a The pressure will increase.
13 a evaporation (or vaporisation)
6 a slowly
b pV = constant
p1V1 = p2V2
p∝ 1
V
8 a gas
[1]
[1]
c
Gas
Shape
Molecules
fixed shape
vibrate about a
fixed position
[2]
shape fills the
container from
the bottom
move around,
close together
[1]
completely fills
the container
move around,
far apart
[1]
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Answers to end-of-chapter questions: Chapter 9
1
b i increases
16 a i bombardment/collisions with air
molecules/particles
[1]
ii any two from
lighter / very small / smaller than smoke
particles / too small to be seen
fast-moving / high kinetic energy
random movement / movement in all
directions
[2]
© Cambridge University Press 2014 IGCSE Physics
[1]
ii air molecules/particles/atoms
bombard/hit walls
molecules faster / higher energy when
temperature raised
(not vibrate faster)
greater force (per unit area) or more
collisions per second
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Answers to end-of-chapter questions: Chapter 9
2
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