Free NEET Physics multiple-choice questions on Thermodynamic Processes. Attempt each question and reveal the answer with a full explanation.
For the reaction C(s) + H 2O(g) CO(g) + H 2(g) , the Δ n g value is: 1 2 0 -1 If 1 mole of an ideal gas is compressed isothermally and reversibly, which of the following is true? ΔU = 0 ΔH 0 w = 0 q = 0 The temperature of the system decreases in an: Adiabatic expansion Isothermal expansion Adiabatic compression Isothermal compression A gas expands from 1 m 3 to 2 m 3 at a constant pressure of 10 5 Pa . The work done by the gas is: 10 5 J 2 10 5 J 0.5 10 5 J 10 2 J In a polytropic process PV n = constant , if n = , the process is: Adiabatic Isothermal Isobaric Isochoric Which of the following processes is reversible Transfer of heat by radiation Transfer of heat by conduction Isothermal compression Electrical heating of a nichrome wire In thermodynamic processes which of the following statements is not true ? In an adiabatic process PV = constant In an adiabatic process the system is insulated from the surroundings In an isochoric process pressure remains constant In an isothermal process the temperature remains constant In which of the following processes, heat is neither absorbed nor released by a system? Isochoric Isothermal Adiabatic Isobaric Two cylinders A and B of equal capacity are connected to each other via a stop cock. A contains an ideal gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated. The stop cock is suddenly opened. The process is : adiabatic isochoric isobaric isothermal A thermodynamic system is taken through the cycle abcda . The work done by the gas along the path bc is: Zero 30 J -90 J -60 J The work done during the expansion of a gas from a volume of 4 dm 3 to 6 dm 3 against a constant external pressure of 3 atm is ( 1 L atm = 101.3 J ): -607.8 J -304.0 J +607.8 J -6 J If a gas expands from V 1 to V 2 against a constant external pressure P ext = 0 , the work done is: Zero P ext (V 2 - V 1) nRT (V 2/V 1) Infinite In an adiabatic process, no heat exchange occurs between the system and surroundings. Which of the following is correct for the reversible adiabatic expansion of an ideal gas? T V - 1 = constant P V = constant P V = constant Both T V - 1 = constant and P V = constant For an ideal gas, the value of the Joule-Thomson coefficient is: Zero Positive Negative Infinite Which of the following conditions is correct for an adiabatic free expansion of an ideal gas into a vacuum? q = 0, T = 0, w = 0 q 0, w = 0, T = 0 q = 0, T < 0, w 0 q = 0, T 0, w = 0 The work done in the expansion of an ideal gas from V 1 to V 2 is maximum when the expansion is: Reversible isothermal Irreversible isothermal Reversible adiabatic Irreversible adiabatic A thermodynamic system is taken through the cycle ABCD as shown in the figure. Heat rejected by the gas during the cycle is: 2PV 4PV 1 2 PV PV During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its temperature. The ratio = C p/C v for the gas is: 1.5 1.33 1.67 2 An ideal gas expands from V 1 to V 2 in three ways: (i) Isothermally (ii) Adiabatically (iii) Isobarically. The work done by the gas is maximum in: Isobaric process Isothermal process Adiabatic process Equal in all If a gas at 27 C is compressed adiabatically to 1/8 th of its initial volume, the final temperature will be (take = 5/3 ): 1200 K 927 C 600 K 450 K Which of the following is zero for an ideal gas during free expansion? All of these Work done Heat change Internal energy change On a pressure-volume ( P-V ) diagram, the slope of an adiabatic curve for an ideal gas is: times the slope of the isothermal curve Equal to the slope of the isothermal curve 1/ times the slope of the isothermal curve Twice the slope of the isothermal curve The work done in the isothermal reversible expansion of an ideal gas is W = -nRT (V 2/V 1) . If the gas is compressed instead, the work done by the surroundings is: Positive Negative Zero Cannot be determined Calculate the work done (in Joules) when 2 moles of an ideal gas expand isothermally and reversibly from 10 L to 100 L at 300 K . ( R = 8.314 J K -1 mol -1 , 10 = 2.303 ) -11488 J -5744 J 11488 J -2494 J During the expansion of an ideal gas into a vacuum (free expansion) in an isolated container, which of the following is correct? Q=0, W=0, U=0 Q 0, W=0, U=0 Q=0, W 0, U=0 Q=0, W=0, U 0 If the heat capacity of a gas at constant pressure is C p = 29.1 J K -1 mol -1 , the ratio of heat capacities is ( R = 8.314 J K -1 mol -1 ): 1.40 1.66 1.33 1.25 For which of the following processes is the work done by the system the greatest, assuming the initial and final volumes are the same for all? Isobaric expansion Isothermal expansion Adiabatic expansion All processes have equal work done For the combustion of benzene: C 6H 6(l) + 15 2 O 2(g) 6CO 2(g) + 3H 2O(l) , what is the value of n g ? -1.5 1.5 -7.5 6 In a Joule-Thomson expansion of an ideal gas, the temperature: Remains constant Decreases Increases Depends on the initial pressure A gas is compressed from 2 L to 1 L at a constant external pressure of 10 atm . The work done ON the system is ( 1 L atm = 101.3 J ): 1013 J -1013 J 10 J 101.3 J In a reversible adiabatic process, the quantity PV is constant. What is the equivalent relation between T and V ? TV -1 = constant T V = constant T/V = constant TV = constant For an ideal gas, the value of the adiabatic bulk modulus at pressure P is: P P P/ Zero Three moles of an ideal gas kept at a constant temperature of 300 K are compressed from a volume of 4 L to 1 L . Calculate the work done on the gas. ( R = 8.314 J K -1 mol -1 ) 10.36 kJ -10.36 kJ 3.45 kJ -3.45 kJ For a process to be both adiabatic and reversible, the change in which thermodynamic property must be zero? Entropy ( S ) Enthalpy ( H ) Internal Energy ( U ) Gibbs Free Energy ( G ) Two cylinders A and B of equal capacity are connected to each other via a stopcock. A contains an ideal gas at standard temperature and pressure (STP). B is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. The process is: Adiabatic and free expansion Isothermal expansion Isobaric expansion Isothermal compression On a P-V diagram, if an adiabatic process and an isothermal process start from the same point, the slope of the adiabatic curve is: times the slope of the isothermal curve Equal to the slope of the isothermal curve 1/ times the slope of the isothermal curve 2 times the slope of the isothermal curve In an isobaric process, the ratio of heat supplied ( dQ ) to the work done ( dW ) for an ideal monoatomic gas is: 5/2 3/2 1 2/5 A thermodynamic system is taken through a cycle ABC as shown in the P-V diagram. The work done by the gas during the cycle is: 2PV 4PV PV Zero In a reversible adiabatic expansion of an ideal gas, the plot of P versus V gives a straight line with a slope of: - -1/ 1 Calculate the work done when 1 mole of an ideal gas is compressed isothermally and reversibly from 1 bar to 10 bar at 300 K . 5744 J -5744 J 2303 J -2303 J The work done by a system in an expansion from V 1 to V 2 is given by W = P dV . If the pressure is given by P = kV (where k is a constant), the work done is: k/2 (V 2 2 - V 1 2) k(V 2 - V 1) k (V 2/V 1) k/2 (V 2 - V 1) 2 The work done during an isothermal reversible expansion of an ideal gas is given by W = -nRT (V 2/V 1) . If the same expansion occurs irreversibly against a constant external pressure P ext , the magnitude of work: Is always less than the reversible work Is always more than the reversible work Is equal to the reversible work Is zero An ideal gas is allowed to expand into a vacuum in a rigid, insulated container. Which of the following is true? Q = 0, W = 0, U = 0 Q 0, W = 0, U = 0 Q = 0, W 0, U = 0 Q = 0, W = 0, U 0 The molar heat capacity of a gas at constant pressure is C p = 2.5R . The degrees of freedom for this gas are: 3 5 6 2 A thermodynamic system is taken through a cycle as shown in the figure. If the cycle is clockwise on a P-V diagram, the net work done by the system is: Positive Negative Zero Infinite The value of ( C p/C v ) for a linear triatomic molecule (like CO 2 ) neglecting vibrational modes is: 1.40 1.67 1.33 1.25 Which relationship is used to find the work done in a reversible adiabatic process? W = [P 2V 2 - P 1V 1] / ( - 1) W = nRT (V 2/V 1) W = P V W = 0 During an adiabatic process, the relationship between temperature ( T ) and pressure ( P ) for an ideal gas is given by: T P 1- = constant T P -1 = constant T P -1 = constant T 1- P = constant For an ideal gas, the slope of an adiabatic curve ( P vs V ) at a point (P, V) is: times the slope of the isothermal curve Equal to the slope of the isothermal curve 1/ times the slope of the isothermal curve Negative of the isothermal slope The Joule-Thomson coefficient ( μ JT ) for an ideal gas is: Zero Positive Negative Infinite The temperature of inversion ( T i ) for a real gas is related to Van der Waals constants a and b by: T i = 2a Rb T i = a Rb T i = a 2Rb T i = 8a 27Rb In a P-V diagram, a system follows a path from (1 atm , 1 L ) to (1 atm , 3 L ) and then to (2 atm , 3 L ) . What is the total work done by the system? 202.6 J 101.3 J 303.9 J 0 J What is the molar heat capacity of an ideal gas during an isothermal process? Infinite ( ) Zero R C v Which of the following is NOT a property of an ideal gas? The internal energy depends on both temperature and volume The molecules have negligible volume There are no intermolecular forces It obeys PV = nRT at all temperatures and pressures The work done during the expansion of a gas from volume V 1 to V 2 is given by W = P dV . If P = a/V where a is a constant, the work done is: a (V 2/V 1) a(V 2 - V 1) a/(V 2 - V 1) a (V 1/V 2) In an adiabatic expansion of an ideal gas, the product TV -1 is constant. This implies that if volume increases: Temperature must decrease Temperature must increase Pressure must remain constant Internal energy must increase In a P-V diagram, the slope of an isothermal curve is M 1 and the slope of an adiabatic curve is M 2 at the same point. The ratio M 2/M 1 is equal to: 1/ - 1 1 Which of the following describes an adiabatic process in a P-V diagram starting from the same point as an isothermal process? The adiabatic curve is steeper than the isothermal curve The isothermal curve is steeper than the adiabatic curve Both curves are identical The adiabatic curve is a horizontal line A gas is taken through the cycle A ; ;B ; ;C ; ;A , as shown. What is the net work done by the gas? 2000 J 1000 J Zero -2000 J During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its temperature. The ratio of C p C v for the gas is 4 3 2 5 3 3 2 A monoatomic gas at a pressure P, having a volume V expands isothermally to a volume 2V and then adiabatically to a volume 16V. The final pressure of the gas is : (take = 5 3 ) 64P 32P P 64 16P A thermodynamic system undergoes cyclic process ABCDA as shown in fig. The work done by the system in the cycle is :- P 0V 0 2P 0V 0 P 0V 0 2 Zero A gas is compressed isothermally to half its initial volume. The same gas is compressed separately through an adiabatic process until its volume is again reduced to half. Then :- Compressing the gas isothermally will require more work to be done. Compressing the gas through adiabatic process will require more work to be done. Compressing the gas isothermally or adiabatically will require the same amount of work. Which of the case (whether compression through isothermal or through adiabatic process) requires more work will depend upon the atomicity of the gas. The volume of 1 mole of an ideal gas with the adiabatic exponent is changed according to the relation V = b T where b = constant. The amount of heat absorbed by the gas in the process if the temperature is increased by T will be : ( 1- +1 )R T R -1 T ( 2- -1 )R T R T -1 One mole of a gas obeying the equation of state P(V-b) = RT is made to expand from a state with coordinates (P 1,V 1) to a state with (P 2,V 2) along a process that is depicted by a straight line on a P–V diagram. Then, the work done is given by 1 2 ,(P 2-P 1)(V 2+V 1+2b) 1 2 ,(P 1+P 2)(V 2-V 1) 1 2 ,(P 2-P 1)(V 2-V 1) 1 2 ,(P 1+P 2)(V 2-V 1+2b) The volume (V) of a monatomic gas varies with its temperature (T), as shown in the graph. The ratio of work done by the gas, to the heat absorbed by it, when it undergoes a change from state A to state B, is 1 3 2 3 2 5 2 7 The work done in expanding 1 mole of an ideal gas from 10 L to 20 L in a vacuum is: Zero RT 2 P(V 2 - V 1) -RT 2 An ideal gas undergoes four different processes from the same initial state as shown in the figure below. Those processes are adiabatic, isothermal, isobaric and isochoric. The curve which represents the adiabatic process among 1, 2, 3 and 4 is 2 3 4 1 The work done in an open vessel at 300 K when 92 g of sodium reacts with water to form NaOH and H 2 is: -4988.4 J 4988.4 J -2494.2 J 2494.2 J Which statement is true for the reversible expansion of an ideal gas into a vacuum? This process is impossible as expansion into a vacuum is always irreversible The entropy change is zero The work done is maximum The temperature remains constant only if it is adiabatic The molar heat capacity of a mixture of 2 moles of Helium and 4 moles of Nitrogen at constant volume is: 13/6 R 11/6 R 17/6 R 5/2 R The work done in expanding a gas from V 1 to V 2 along the path P = aV (where a is a constant) is: a(V 2 2 - V 1 2)/2 a(V 2 - V 1) a (V 2/V 1) a(V 2 2 + V 1 2)/2 In a polytropic process PV n = constant , the molar heat capacity C of an ideal gas is given by: C = C v + R 1-n C = C p + R 1-n C = C v + R n-1 C = R -1 + R 1-n For a monoatomic ideal gas, what is the work done in a polytropic process PV 2 = constant when the gas expands from V 1 to V 2 ? P 2V 2 - P 1V 1 (P 1V 1 - P 2V 2)/2 P 1V 1 - P 2V 2 (P 2V 2 - P 1V 1)/2 In an adiabatic expansion, the temperature of one mole of an ideal monatomic gas ( =5/3 ) decreases from 60 K to 50 K. The work done by the gas in the process is: [Take the universal gas constant as R=8.3 J mol -1 K -1 ] 41.5 J 83 J 124.5 J 166 J One mole of an ideal monatomic gas undergoes a cyclic process as shown in the figure. The total heat supplied to the gas is: 400 J 500 J 600 J 800 J The correct relationship for an adiabatic process involving an ideal gas is: TV -1 = constant T V = constant P V = constant PV = constant A gas expands isothermally and irreversibly from 10 L to 20 L against a constant external pressure of 1 atm. The work done is: -10 L-atm -20 L-atm +10 L-atm Zero