Topic 3 &10 Review Thermodynamics

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Madison Warren
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1 Name: Date: Topic 3 &10 Review Thermodynamics 1. The kelvin temperature of an object is a measure of A. the total energy of the molecules of the object. B. the total kinetic energy of the molecules of the object. C. the maximum energy of the molecules of the object. D. the average kinetic energy of the molecules of the object. 2. The internal energy of a solid substance is equal to the A. average kinetic energy of the molecules. B. total kinetic energy of the molecules. C. total potential energy of the molecules. D. total potential and total kinetic energy of the molecules. 3. Some liquid is contained in a shallow dish that is open to the atmosphere. The rate of evaporation of the liquid does not depend on A. the temperature of the liquid. B. the temperature of the atmosphere. C. the depth of the liquid. D. the pressure of the atmosphere. 4. The length of the mercury column in a thermometer is L 100 at 100 C and L 0 at 0 C. Which of the following gives the temperature when the length of the mercury column is L T? LT A. 100 C L 100 B. C. ( L L ) 100 L T 0 ( L100 LT ) ( L L ) C 100 C 1

2 D. ( LT L0 ) ( L L ) C 5. Three bodies X, Y and Z are at temperatures θ X, θ Y and θ Z respectively. Thermal energy passes freely from Y to X and also from Z to X, as illustrated below. X X Z Z Y Y The direction of flow of thermal energy, if any, between Y and Z is unknown. What can be deduced about the temperatures θ X, θ Y and θ Z? A. θ X = (θ Y +θ Z ) B. θ Y = θ Z C. θ Y > θ X D. θ X > θ Z 6. A metal block of mass M is heated. The graph shows the variation with thermal energy H supplied to the block of its temperature rise θ. n 0 0 H The gradient of the straight-line graph is n. The specific heat capacity of the metal is A. 1. Mn B. 1. n C. Mn. D. n. 2

3 7. An ideal gas is contained in a cylinder by a piston. The volume of the gas is decreased by moving the piston rapidly in the direction shown. gas piston moved rapidly in this direction The average speed of the gas molecules is initially increased because the molecules A. have a smaller volume in which to move. B. make more collisions in unit time with the cylinder walls and piston. C. have energy transferred to them as they collide with the moving piston. D. make more collisions with each other in unit time. 8. A sample of an ideal gas is contained in a cylinder. The volume of the gas is suddenly decreased. A student makes the following statements to explain the change in pressure of the gas. I. The average kinetic energy of the gas atoms increases. II. III. The atoms of the gas hit the walls of the cylinder more frequently. There are more atoms that are able to collide with the walls of the cylinder. Which of these statements is true? A. I and II only B. I and III only C. II and III only D. I, II and III 9. A gas is contained in a cylinder fitted with a piston as shown below. When the gas is compressed rapidly by the piston its temperature rises because the molecules of the gas A. are squeezed closer together. B. collide with each other more frequently. C. collide with the walls of the container more frequently. D. gain energy from the moving piston. 3

4 10. When a gas in a cylinder is compressed at constant temperature by a piston, the pressure of the gas increases. Consider the following three statements. I. The rate at which the molecules collide with the piston increases. II. III. The average speed of the molecules increases. The molecules collide with each other more often. Which statement(s) correctly explain the increase in pressure? A. I only B. II only C. I and II only D. I and III only 11. Two objects X and Y are made of the same material. Object X is more massive than object Y. Both objects are at the same temperature. Which of the following correctly compares the average kinetic energy and also the total energy of the molecules in the objects? average kinetic energy of the molecules in X and Y total energy of the molecules in X and Y A. same greater in X than in Y B. same less in X than in Y C. greater in X than in Y same D. less in X than in Y same 4

5 12. A large mass M of ice of specific latent heat L is at its melting point (0 C). A small mass m of water at θ C is poured on to the block of ice. The specific heat capacity of water is S. Which one of the following is a correct expression for the mass of ice melted? A. B. C. D. ml Sθ msθ L MSθ L MS Sθ 13. The specific latent heat of fusion of a substance is defined as the amount of thermal energy required to change the phase of A. the substance at constant temperature. B. unit mass of the substance to liquid at constant temperature. C. unit mass of the substance at constant temperature. D. the substance to gas at constant temperature. 14. The specific latent heat of vaporization of a substance is the quantity of energy required to A. raise the temperature of a unit mass of a substance by one degree Celsius. B. convert a unit mass of liquid to vapour at constant temperature and pressure. C. convert a unit mass of solid to vapour at constant temperature and pressure. D. convert a unit mass of liquid to vapour at a temperature of 100 C and a pressure of one atmosphere. 5

6 15. Heating water electrically The diagram below shows part of the heating circuit of a domestic shower. insulated wire 240V supply water pipe cold water 14 C insulated heating element hot water 40 C Cold water enters the shower unit and flows over an insulated heating element. The heating element is rated at 7.2 kw, 240 V. The water enters at a temperature of 14 C and leaves at a temperature of 40 C. The specific heat capacity of water is J kg 1 K 1. (a) Describe how thermal energy is transferred from the heating element to the water (3) (b) Estimate the flow rate in kg s 1 of the water (4) (c) Suggest two reasons why your answer to (b) is only an estimate

7 (d) Calculate the current in the heating element when the element is operating at 7.2 kw (e) Explain why, when the shower unit is switched on, the initial current in the heating element is greater than the current calculated in (d) (f) In some countries, shower units are operated from a 110 V supply. A heating element operating with a 240 V supply has resistance R 240 and an element operating from a 110 V supply has resistance R 110. (i) Deduce, that for heating elements to have identical power outputs R R 110 = (3) (ii) Using the ratio in (i), describe and explain one disadvantage of using a 110 V supply for domestic purposes. 7

8 (Total 18 marks) 16. This question is about an ideal gas. (a) The pressure P of a fixed mass of an ideal gas is directly proportional to the kelvin temperature T of the gas. That is, P T. State (i) the relation between the pressure P and the volume V for a change at constant temperature; (ii) the relation between the volume V and kelvin temperature T for a change at a constant pressure. (b) The ideal gas is held in a cylinder by a moveable piston. The pressure of the gas is P 1, its volume is V 1 and its kelvin temperature is T 1. The pressure, volume and temperature are changed to P 2, V 2 and T 2 respectively. The change is brought about as illustrated below. / P1, V 1, T1 P, V, T P2, V 2, T2 2 1 heated at constant volume to pressure P and temperature T 2 / heated at constant pressure to volume V 2 and temperature T 2 State the relation between (i) P 1, P 2, T 1 and T. (ii) V 1, V 2, T and T 2. 8

9 (c) Use your answers to (b) to deduce, that for an ideal gas PV = KT where K is a constant (4) (Total 8 marks) 17. This question is about an ideal gas and entropy. (a) A fixed mass of an ideal gas is compressed from volume V 1 to volume V 2 at constant temperature. The variation with volume V of the pressure p of the gas is shown below. p V 2 V 1 V On the diagram above, draw a line to show the variation of pressure p as the volume of the gas is changed from V 1 to V 2 without allowing any thermal energy to enter or leave the gas. (b) On the diagram in (a), identify (i) (ii) with the letter G, the line that represents the change that requires the greater amount of work done on the gas. by shading an area of the diagram, the part of the diagram that represents the difference between the work done in the two changes. 9

10 (c) For the compression of the gas at constant temperature, deduce what change, if any, occurs in the entropy of the gas and of its surroundings. the gas: the surroundings: This question is about a heat engine.... (3) (Total 7 marks) A quantity of an ideal gas is used as the working substance of a heat engine. The cycle of operation of the engine is shown in the p-v diagram below. 5 p / 10 Pa 12.0 A B C V / 10 m The temperature of the gas at A is 300 K. (a) Calculate the temperature, at B, of the gas (b) During the change A B the change in internal energy of the gas is 7.2 kj. Determine the amount of thermal energy transferred

11 (c) State why, for the change B C, the change in the internal energy of the gas is numerically the same as that in (b) (d) The work done on the gas in the change C A is 2.6 kj. Calculate (i) the net work done in one cycle (ii) the efficiency (Total 10 marks) 11

12 19. Thermodynamics The graph below shows the variation with volume V of the pressure p for two isothermal changes of two ideal gases X and Y. The gases have the same number of moles. The dots indicate two particular states of the gases, (p X, V X ) and (p Y, V Y ). p X Y p X p Y 0 0 V V X Y V (a) State what is meant by an isothermal change (b) Explain whether gas X in the state (p X, V X ) is at a higher or lower temperature than gas Y in the state (p Y, V Y )

13 (c) Gas Y is compressed adiabatically from state (p Y, V Y ) until it reaches the pressure p X. (i) Explain whether the temperature of gas Y will increase, decrease or stay the same during this process. (ii) On the graph opposite, draw a line to represent this adiabatic compression of gas Y. (3) (3) (d) On the graph opposite, shade the area that represents the work done when gas X is compressed isothermally from volume V Y to volume V X. (Total 11 marks) 20. This question is about thermodynamic processes. (a) State what is meant by the concept of internal energy of an ideal gas (b) The diagram below shows the variation with volume of the pressure of a fixed mass of an ideal gas. pressure B A C 0 0 volume The change from B to C is an isothermal change at 546 K. At point A, the pressure of the gas is Pa, the volume of the gas is 22.0 m 3 and the temperature of the gas is 273 K. 13

14 (i) State the temperature of the gas at point C; (ii) Calculate the volume of the gas at point C. (c) For the change from B to C, J of thermal energy is transferred to the gas. (i) State the work done in the change from A to B. (ii) Determine the work done during the change C to A. (iii) Explain whether the work in (ii) is done by the gas or on the gas. (iv) Determine the work done by the gas during one cycle ABCA. (Total 11 marks) 14

15 21. This question is about thermodynamic processes. (a) State what is meant by an adiabatic change (b) The diagram below shows the pressure-volume (p-v) changes for one cycle of the working substance of a refrigerator. p / 5 10 Pa V / m On the diagram above, (i) (ii) (iii) draw arrows to show the direction of the changes; label with the letter A an isobaric change; label with the letter B the change during which thermal energy is transferred to the working substance. 15

16 (c) Use data from the diagram in (b) to estimate the work done during one cycle of the working substance (3) (d) (i) By referance to entropy change, state the second law of thermodynamics. (ii) The cycle of the working substance in (b) reduces the temperature inside the refrigerator. Explain how your statement in (d)(i) is consistent with the operation of a refrigerator. (3) (Total 11 marks) 22. This question is about the first law of thermodynamics. (a) Describe what is meant by the internal energy of an ideal gas (b) The internal energy of an ideal gas increases by an amount U. During this process, an amount q of thermal energy is transferred to the gas and the gas does an amount w of external work. (i) Use the first law of thermodynamics to state a relation between U, q and w. 16

17 (ii) Suggest how the state of an ideal gas may be changed such that each of the following conditions is met separately. U = 0... w = 0... q = 0... (3) (Total 6 marks) 17

Distinguish between an isothermal process and an adiabatic process as applied to an ideal gas (2)

1. This question is about thermodynamic processes. (a) Distinguish between an isothermal process and an adiabatic process as applied to an ideal gas.......... An ideal gas is held in a container by a moveable