15.3. Kinetic theory of gases
A subsection of Physics, 9702, through 15. Ideal gases
Listing 10 of 64 questions
A gas molecule has a mass of 6.64 × 10−27 kg and a speed of 1250 m s−1. The molecule collides normally with a flat surface and rebounds with the same speed, as shown in . molecule molecule before collision after collision flat surface flat surface Calculate the change in momentum of the molecule. change in momentum = N s Use the kinetic model to explain the pressure exerted by gases. Explain the effect of an increase in density, at constant temperature, on the pressure of a gas.
9702_s15_qp_22
THEORY
2015
Paper 2, Variant 2
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An ideal gas is assumed to consist of atoms or molecules that behave as hard, identical spheres that are in continuous motion and undergo elastic collisions. State two further assumptions of the kinetic theory of gases. 1. 2. Helium-4 (4 2He) may be assumed to be an ideal gas. Show that the mass of one atom of helium-4 is 6.6 × 10−24 g. The mean kinetic energy EK of an atom of an ideal gas is given by the expression EK = 3 2 kT. Calculate the root-mean-square (r.m.s.) speed of a helium-4 atom at a temperature of 27 °C. r.m.s. speed = m s−1
9702_s16_qp_41
THEORY
2016
Paper 4, Variant 1
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An ideal gas is assumed to consist of atoms or molecules that behave as hard, identical spheres that are in continuous motion and undergo elastic collisions. State two further assumptions of the kinetic theory of gases. 1. 2. Helium-4 (4 2He) may be assumed to be an ideal gas. Show that the mass of one atom of helium-4 is 6.6 × 10−24 g. The mean kinetic energy EK of an atom of an ideal gas is given by the expression EK = 3 2 kT. Calculate the root-mean-square (r.m.s.) speed of a helium-4 atom at a temperature of 27 °C. r.m.s. speed = m s−1
9702_s16_qp_43
THEORY
2016
Paper 4, Variant 3
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Describe the motion of molecules in a gas, according to the kinetic theory of gases. Describe what is observed when viewing Brownian motion that provides evidence for your answer in . At a pressure of 1.05 × 105 Pa and a temperature of 27 °C, 1.00 mol of helium gas has a volume of 0.0240 m3. The mass of 1.00 mol of helium gas, assumed to be an ideal gas, is 4.00 g. Calculate the root-mean-square (r.m.s.) speed of an atom of helium gas for a temperature of 27 °C. r.m.s. speed = m s–1 Using your answer in , calculate the r.m.s. speed of the atoms at 177 °C. r.m.s. speed = m s–1
9702_s17_qp_41
THEORY
2017
Paper 4, Variant 1
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Describe the motion of molecules in a gas, according to the kinetic theory of gases. Describe what is observed when viewing Brownian motion that provides evidence for your answer in . At a pressure of 1.05 × 105 Pa and a temperature of 27 °C, 1.00 mol of helium gas has a volume of 0.0240 m3. The mass of 1.00 mol of helium gas, assumed to be an ideal gas, is 4.00 g. Calculate the root-mean-square (r.m.s.) speed of an atom of helium gas for a temperature of 27 °C. r.m.s. speed = m s–1 Using your answer in , calculate the r.m.s. speed of the atoms at 177 °C. r.m.s. speed = m s–1
9702_s17_qp_43
THEORY
2017
Paper 4, Variant 3
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Use one of the assumptions of the kinetic theory of gases to explain why the potential energy of the molecules of an ideal gas is zero. The average translational kinetic energy EK of a molecule of an ideal gas is given by the expression EK = 1 2m 〈c2〉 = 3 2 kT where m is the mass of a molecule and k is the Boltzmann constant. State the meaning of the symbol 〈c2〉, T. A cylinder of constant volume 4.7 × 104 cm3 contains an ideal gas at pressure 2.6 × 105 Pa and temperature 173 °C. The gas is heated. The thermal energy transferred to the gas is 2900 J. The final temperature and pressure of the gas are T and p, as illustrated in . 2900 J 4.7 × 104 cm3 p T 4.7 × 104 cm3 2.6 × 105 Pa 173 °C Calculate 1. the number N of molecules in the cylinder, N = 2. the increase in average kinetic energy of a molecule during the heating process. increase = J Use your answer in part 2 to determine the final temperature T, in kelvin, of the gas in the cylinder. T = K
9702_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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State what is meant by an ideal gas. Use one of the basic assumptions of the kinetic theory to explain what can be deduced about the potential energy associated with the random motion of molecules in an ideal gas. A sample of 0.26 m3 of an ideal gas is at pressure 2.0 × 105 Pa and temperature 290 K. Determine: the number N of molecules of the gas N = the average translational kinetic energy EK of one molecule of the gas EK = J the internal energy of the gas. Explain your reasoning. internal energy = J The volume V of the gas in is now varied, keeping its pressure constant. On , sketch the variation with V of the internal energy U of the gas. V U
9702_s24_qp_41
THEORY
2024
Paper 4, Variant 1
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