Exam code: H556
Define the internal energy of a substance.
[1]
A block of paraffin wax is melting at a constant temperature of 52 °C. Use the behaviour of paraffin molecules to describe and explain the changes to the internal energy of the molecules of the paraffin wax as it melts.
[4]
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A 150 W heater is used to heat 25 g of ice in a sealed and well-insulated container. The initial temperature of the ice is –20°C. The graph shows the variation of temperature θ with time t as the ice is heated.
There are three distinct regions of the graph, X, Y and Z.
i) Use the graph to determine the specific heat capacity c of the ice.
c = .......................................... J kg–1K–1 [3]
ii)
Use the graph to determine the specific latent heat of fusion of ice Lf
Lf = ............................................... J kg–1 [2]
iii)
Use the graph to compare the specific heat capacities of ice and water. Explain your answer.
[2]
i) Describe the motions of the molecules in region X and in region Z.
[2]
ii) The internal energy of the ice increases from t = 0 to t = 77 s. Complete the table below using the following key for the physical quantities:
K = kinetic energy of molecules
P = potential energy of molecules.
Region | Physical quantity, or quantities, that increases as time increases | Physical quantity, or quantities, that remain constant as time increases |
X |
|
|
Y |
|
|
Z |
|
|
[3]
iii) State the temperature of the ice at which its molecules have zero kinetic energy.
[1]
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A plastic kettle is filled with 0.60 kg of water at a temperature of 20 °C. A 2.2 kW electric heater is used to heat the water for a time of 4.0 minutes.
Calculate the total energy supplied by the heater during the time of 4.0 minutes.
energy = ..................................... J [2]
The specific heat capacity of water is 4200 J kg−1 K−1 and the specific latent heat of vaporization of water is 2.3 × 106 J kg−1. The boiling point of water is 100 °C.
Calculate the mass of water remaining in the kettle after 4.0 minutes. Assume that all the thermal energy from the heater is transferred to the water.
mass of water remaining = .................................. kg [4]
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Explain what is meant by the internal energy of a substance.
A student immerses a 3.0 kW electric heater in an insulated beaker of water. The heater is switched on, and after 140 s the water reaches boiling point.
The table gives data collected during the experiment.
Mass of beaker | 55 g |
Initial mass of beaker and water | 1170 g |
Initial temperature of water | 10 °C |
Final temperature of water | 100 °C |
Calculate the specific heat capacity of water if the thermal capacity of the beaker is negligible. State an appropriate unit.
specific heat capacity = .................................................. unit ..............................
A sample of solid material of mass 0.17 kg is supplied with energy at a constant rate. The specific heat capacity of the solid material is 1500 J kg−1 K−1. During heating, the temperature of the material is recorded at regular time intervals.
Fig. 18.1 shows the variation with time of the temperature for the material.
Fig. 18.1
Assume there is no heat exchange with the surroundings.
Show that energy is supplied to the material at a rate of 34 W.
Describe how an electrical method can be used to determine the specific latent heat of vaporisation L of water, and how the data can be analysed to obtain an accurate value for L.
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A heater is used to heat water in a beaker.
(i) Before switching on, the metal heater and the water are both at room temperature.
Describe the motion of the atoms of the metal heater and of the water molecules.
[3]
(ii) The heater is now switched on.
The power of the heater is 200 W. The mass of the water in the beaker is 500 g. It takes 10.0 minutes to increase the temperature of the water in the beaker from 20 °C to 60 °C.
Calculate the energy transferred from the water to the beaker and the surroundings.
specific heat capacity of water = 4200 J kg−1 K−1
energy transferred = ........................................ J
[3]
A student is carrying out an experiment to determine the specific latent heat of fusion Lf of ice. The student has two sets of apparatus next to each other on the laboratory bench, as shown in Fig. 17.1 and Fig. 17.2.
Fig. 17.1 and Fig. 17.2
Both funnels are identical and have the same mass of crushed ice at 0 °C.
The current in the heater is 5.0 A and the potential difference across it is 12 V.
Fig. 17.3 shows the variation of mass of water m collected in each beaker with time t.
Fig. 17.3
Describe and explain the shape of the two graphs in Fig. 17.3 and use them to determine the specific latent heat of fusion Lf of ice.
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A substance can exist as a crystalline solid, a liquid or a gas. A solid sample of the substance is placed in a sealed container and heated at a constant rate until it changes into a gas.
Fig. 21 shows the variation with time t of the temperature θ for the substance.
Fig. 21
Use the kinetic theory of matter to describe the solid phase (section AB) and the liquid phase (section CD) in terms of the motion and arrangement of the molecules of the substance.
Section AB:
Section CD:
[4]
Use Fig. 21 to explain how the specific heat capacity of the liquid compares with the specific heat capacity of the solid.
[2]
State what is meant by the internal energy of the substance.
[1]
Beyond the point E in Fig. 21, the substance behaves as an ideal gas.
i) The mass of a gas molecule is 4.8 × 10–26 kg. Calculate the root mean square speed of the gas molecules at a temperature of 250°C.
root mean square speed = ................................. ms–1 [3]
ii) Calculate the internal energy of 1.3 moles of the gas at 250°C.
internal energy = ................................... J [3]
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