1.
This question is about an experiment to measure the temperature of a flame.
(a)
Define heat (thermal) capacity.
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(1)
A piece of metal is held in the flame of a Bunsen burner for several minutes. The metal is then
quickly transferred to a known mass of water contained in a calorimeter.
flame
water
calorimeter
container
Bunsen burner
lagging (insulation)
The water into which the metal has been placed is stirred until it reaches a steady temperature.
(b) Explain why
(i)
the metal is transferred as quickly as possible from the flame to the water;
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(1)
(ii) the water is stirred.
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(1)
The following data are available:
heat capacity of metal
= 82.7 J K–1
heat capacity of the water in the calorimeter = 5.46 × 102 J K–1
(c)
heat capacity of the calorimeter
= 54.6 J K–1
initial temperature of the water
= 288 K
final temperature of the water
= 353 K
Assuming negligible energy losses in the processes involved, use the data to calculate the
temperature T of the Bunsen flame.
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(4)
1
2.
This question is about thermal physics.
(a)
Explain why, when a liquid evaporates, the liquid cools unless thermal energy is supplied
to it.
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(3)
(b)
State two factors that cause an increase in the rate of evaporation of a liquid.
1. .................................................................................................................................
2. .................................................................................................................................
(2)
(c)
Some data for ice and for water are given below.
Specific heat capacity of ice
Specific heat capacity of water
Specific latent heat of fusion of ice
= 2.1 × 103 J kg–1 K–1
= 4.2 × 103 J kg–1 K–1
= 3.3 × 105 J kg–1
A mass of 350 g of water at a temperature of 25°C is placed in a refrigerator that extracts
thermal energy from the water at a rate of 86 W.
Calculate the time taken for the water to become ice at –5.0°C.
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(4)
3.
This question is about specific heat capacity and specific latent heat.
(a)
Define specific heat capacity.
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(1)
(b)
Explain briefly why the specific heat capacity of different substances such as aluminium
and water are not equal in value.
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(2)
2
A quantity of water at temperature θ is placed in a pan and heated at a constant rate until some
of the water has turned into steam. The boiling point of the water is 100°C.
(c)
(i)
Using the axes below, draw a sketch-graph to show the variation with time t of the
temperature θ of the water. (Note: this is a sketch-graph; you do not need to add
any values to the axes.)
(1)
100°C
°C
0
time at which
heating starts
(ii)
t
time at which
water starts to boil
Describe in terms of energy changes, the molecular behaviour of water and steam
during the heating process.
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(5)
Thermal energy is supplied to the water in the pan for 10 minutes at a constant rate of 400 W.
The thermal capacity of the pan is negligible.
(d)
(i)
Deduce that the total energy supplied in 10 minutes is 2.4 × 105 J.
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(1)
3
(ii)
Using the data below, estimate the mass of water turned into steam as a result of
this heating process.
initial mass of water
= 0.30 kg
initial temperature of the water θ
= 20°C
specific heat capacity of water
= 4.2 × 103 J kg–1 K–1
specific latent heat of vaporization of water = 2.3 × 106 Jkg–1
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(3)
(iii)
Suggest one reason why this mass is an estimate.
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(1)
(Total 14 marks)
4.
This question is about the change of phase (state) of ice.
A quantity of crushed ice is removed from a freezer and placed in a calorimeter. Thermal energy
is supplied to the ice at a constant rate. To ensure that all the ice is at the same temperature, it is
continually stirred. The temperature of the contents of the calorimeter is recorded every 15
seconds.
The graph below shows the variation with time t of the temperature θ of the contents of the
calorimeter. (Uncertainties in the measured quantities are not shown.)
20
15
10
5
°C
0
–5
–10
–15
–20
0
25
50
75
100
t/s
125
150
175
200
4
(a)
On the graph above, mark with an X, the data point on the graph at which all the ice has
just melted.
(1)
(b) Explain, with reference to the energy of the molecules, the constant temperature region of
the graph.
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(3)
The mass of the ice is 0.25 kg and the specific heat capacity of water is 4200 Jkg–1K–1.
(c)
Use these data and data from the graph to
(i)
deduce that energy is supplied to the ice at the rate of about 530 W.
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(3)
(ii)
determine the specific heat capacity of ice.
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(3)
(iii)
determine the specific latent heat of fusion of ice.
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(2)
5
(d)
State what property of the molecules of the ice is measured by a change in entropy.
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(1)
(e)
State, in terms of entropy change, the second law of thermodynamics.
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(1)
(f)
State what happens to the entropy of water as it freezes. Outline how this change in
entropy is consistent with the second law of thermodynamics.
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(4)
5.
Temperature and thermal energy
(a)
Outline how a temperature scale is constructed.
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(2)
(b)
Discuss why even an accurate thermometer may affect the reliability of a temperature
reading.
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(2)
6
(c)
(i)
Define specific heat capacity.
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(2)
(ii)
The table below gives data for water and ice.
specific heat capacity of water
4.2 kJ kg–1 K–1
specific latent heat of fusion of ice
330 kJ kg–1
A beaker contains 450 g of water at a temperature of 24C. The thermal (heat)
capacity of the beaker is negligible and no heat is gained by, or lost to, the
atmosphere. Calculate the mass of ice, initially at 0C, that must be mixed with the
water so that the final temperature of the contents of the beaker is 8.0C.
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(4)
(d)
(i)
Distinguish between evaporation and boiling.
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(2)
(ii)
Explain, in terms of molecular behaviour, why boiling involves a transfer of
thermal energy with no change in temperature.
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(3)
(Total 15 marks)
7
6.
The physics of cooling
(a)
Explain what is meant by the temperature of a substance.
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(2)
A thermometer is placed in a liquid contained in an open beaker. The reading of the
thermometer is recorded at regular intervals. The variation with time t of the temperature  is
shown below.
/ C
80
70
60
50
40
30
20
10
0
0
1000 2000 3000 4000 5000 6000 7000 8000
t/s
(b) The temperature of the surroundings is 20C. On the graph continue the line to show the
variation with time of the temperature for the next 3000 s.
(2)
(c)
By reference to the graph, state and explain the rate of loss of thermal energy from the
substance between
(i)
0 and 600 s;
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(2)
(ii)
600 and 1800 s.
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(4)
8
The mass of the liquid is 0.11 kg and the specific heat capacity of the liquid is 1300 J kg–1 K–1.
(d)
(i)
Use the graph to deduce that the rate of loss of thermal energy at time t = 600 s is
approximately 4 W.
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(3)
(ii)
Calculate the specific latent heat of fusion of the liquid.
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(3)
(Total 16 marks)
9
1.
(a)
(b)
the amount of energy / heat required to raise the temperature of a
substance / object through 1K / °C;
(i)
to ensure that the temperature of the metal does not change during
the transfer / negligible thermal energy / heat is lost during
the transfer;
1
1
Do not accept metal and water at same temperature.
(ii)
(c)
to ensure that all parts of the water reach the same temperature;
energy lost by metal
energy gained by water
energy gained by calorimeter
equate energy lost to energy gained to get
= 82.7 × (T – 353) J;
= 5.46 × 102 × 65 J;
= 54.6 × 65 J;
T = 825 K;
1
4
Award [2 max] if any energy term is missed.
[7]
2.
(a)
more energetic molecules leave surface;
mean kinetic energy of molecules in liquid decreases;
and mean kinetic energy depends on temperature;
3
Award [2] if mean not mentioned.
(b)
eg larger surface area;
increased draught;
higher temperature;
lower vapour pressure;
2 max
Award [1] if candidate merely identifies two factors.
(c)
energy to be extracted = 0.35 × 4200 × 25;
+0.35 × 330 000;
+0.35 × 2100 × 5;
= 156 000 J
156 000
time =
= 1800 s;
86
4
Allow ecf if one term incorrect or missing.
[9]
3.
(a)
(b)
specific heat capacity is the amount of energy required to raise the
temperature of unit mass through 1 K;
1
raising the temperature means increasing the KE of the molecules;
there are different numbers of molecules of different mass in unit mass
of aluminium and water (accept different densities) and therefore different
amounts of energy will be needed / OWTTE;
2
10
(c)
(i)
100°C
°C
0
time at which
heating starts
t
time at which
water starts to boil
general shape (but constant  range must be clear);
(ii)
1
  100°C:
the KE of the molecules is increasing;
(d)
100°C:
when the water starts to change phase, there is no further increase in KE;
the energy goes into increasing the PE of the molecules;
so increasing their separation;
until they are far enough apart to become gas / their molecular bonds are
broken / until they are effectively an infinite distance apart / OWTTE;
5
(i)
total energy supplied = 400 × 600 = 2.4 ×105 J;
1
(ii)
energy required to raise temperature of water = 0.30 × 80 × 4.2 × 103
= 1.0 × 105 J;
energy available to convert water to steam = (2.4 – 1.0) × 105 = 1.4 × 105 J;
(1.4  10 5 )
mass of water converted to steam
=
 60 g;
3
2.3  10 6
(iii)
energy is lost to the surroundings (must specify where the energy is lost) /
water might bubble out of pan whilst boiling / anything sensible;
1 max
[14]
4.
(a)
(165, 0);
1
(b)
Look for these points:
to change phase, the separation of the molecules must increase;
Some recognition that the ice is changing phase is needed.
so all the energy input goes to increasing the PE of the molecules;
Accept something like “breaking the molecular bonds”.
KE of the molecules remains constant, hence temperature remains constant;
3
If KE mentioned but not temperature then assume they know
that temperature is a measure of KE.
11
(c)
(i)
(ii)
(iii)
time for water to go from 0 to 15°C = 30 s;
energy required = ms = 0.25 × 15 × 4 200 = 15 750 J;
energy
power =
= 525 W  530 W;
time
ice takes 15 s to go from –15°C to 0;
energy supplied = 15 × 530 J;
(530  15)
sp ht =
= 2100 J kg–1 K–1;
(15  0.25)
time to melt ice =150 s;
(150  530)
L=
= 320 kJ kg–1;
0.25
3
3
2
(d)
the degree of disorder / order (of the molecules of the ice);
1
(e)
in any process, (reaction, event etc) the overall entropy of the
universe / a closed system increases ;
1
(f)
entropy decreases;
Award [1] each for any of these main points, up to [3 max].
when water freezes it gives out energy (heat);
therefore speed (KE) of surrounding air molecules increases;
the air surrounding the ice is therefore in a more disordered state;
therefore disorder (entropy) of the universe increases;
4 max
[18]
5.
Temperature and thermal energy
(a)
(b)
property measured at two known temperatures (and at unknown
temperature);
(temperature calculated) assuming linear change of property with
temperature;
Award [1] for descriptions of constructing a thermometer.
2
thermometer absorbs (thermal) energy / heat from the body / has a thermal
capacity; so changes temperature of body;
or
time taken for (thermal) energy / heat to be conducted into thermometer;
so may not be able to follow changing temperature;
(c)
(i)
2
quantity of (thermal) energy / heat required to raise temperature of
unit mass;
by one degree;
or
c
Q
;
m θ
with Q, m and  explained;
2
12
(ii)
(d)
(i)
(ii)
m  330;
+m  4.2  8;
= 0.45  4.2  16;
m = 0.083kg;
Award [2 max] for an answer m = 0.092 kg  ignoring ice-water.
4
(both are change from liquid  vapour phase)
evaporation:
occurs at surface of liquid;
occurs at all temperatures;
boiling:
occurs in the body of the liquid;
occurs at one temperature / boiling point;
2
separation of molecules increases in the change from liquid to vapour
phase;
this involves an increase in potential energy;
but temperature observed to change only when kinetic energy changes;
3
[15]
6.
The physics of cooling
(a)
temperature is proportional to a measure of the average kinetic energy;
of the molecules of the substance;
or:
idea that temperature shows natural direction of the flow of thermal energy;
from high to low temperature / OWTTE; (do not accept “hot to cold”)
2
Award [1 max] for a rough and ready answer and [2 max] for a more
detailed answer.
(b)
(c)
a curve of gradually decreasing rate of loss of temperature;
that is asymptotic to 20C;
Award [0] for a straight-line graph.
(i)
(ii)
2
temperature is falling because of thermal energy transfer to the
surroundings;
with a decreasing rate;
the rate thermal energy transfer / heat loss in this region is greater;
because the temperature difference with the surroundings is greater
/ OWTTE;
2
realization that substance is still losing thermal energy;
1
Award [3 max] for other relevant points:
eg liquid and solid present / phase change taking place;
temperature stays constant until no more liquid;
at a constant rate;
loss of PE of atoms = thermal energy transfer;
because PE decreases;
KE of atoms constant;
4
Award [2 max] for an answer that fails to realize that the liquid
solidifies.
13
(d)
(i)
calculation of the temperature rate of change in the range
(2.4  3.5)  102Cs1;
Q
Q
 mc
;
t
t
= 0.11  1300  2.9  102;
~ 4(1)W;
(ii)
3
energy lost while solidifying E = 3600  6000J;
L
E
;
m
L = 33  55kJ kg1;
3
[16]
14