Chapter 6

When \(\mathrm{NH}_{4} \mathrm{Cl}\) is warmed with \(\mathrm{NaOH}\) in a test tube it is a case of (a) Open system (b) Closed system (c) Isolated system (d) Both a, c

The enthalpy change of a reaction does not depend on (a) initial and final enthalpy change of reaction (b) state of reactants and products (c) different intermediate reactions (d) nature of reactants and products

For an ideal gas Joule-Thomson coefficient is (a) positive (b) negative (c) zero (d) dependent on molecular weight

If the value of \(\mathrm{AH}\) in a reaction is positive, then the reaction is called (a) exothermic (b) endothermic (c) polymorphic (d) polytropic

Molar heat capacity at constant \(\mathrm{P}\) for a substance is equal to (a) \(\left(\delta_{\mathrm{U}} / \delta_{\mathrm{T}}\right)_{\mathrm{v}}\) (b) \(\left(\delta_{H} / \delta_{\mathrm{T}}\right)_{\mathrm{V}}\) (c) \(\left(\delta_{\mathrm{u}} / \delta_{\mathrm{T}}\right)_{\mathrm{p}}\) (d) \(\left(\delta_{\mathrm{H}} / \delta_{\mathrm{T}}\right)_{\mathrm{P}}\)

Plants and living beings are examples of (a) isolated system (b) adiabatic system (c) open system (d) closed system

In thermodynamics, a process is called reversible when (a) the surroundings are always in equilibrium with the system (b) there is no boundary between system and sur roundings (c) the surroundings and system change into each other (d) the system changes into the surroundings sponta neously

If a gas at constant temperature and pressure expands, then its (a) internal energy decreases (b) entropy increases and then decreases (c) internal energy increases (d) internal energy remains constant

If a gas absorbs \(200 \mathrm{~J}\) of heat and expands by 500 \(\mathrm{cm}^{3}\) against a constant pressure of \(2 \times 10^{\mathrm{s}} \mathrm{Nm}^{-2}\), then change in internal energy is (a) \(-200 \mathrm{~J}\) (b) \(-100 \mathrm{~J}\) (c) \(+100 \mathrm{~J}\) (d) \(+300 \mathrm{~J}\)

The internal energy of a substance does not depend upon (a) translational energy (b) vibrational energy (c) energy due to gravitational pull (d) rotational energy

Which one of the following statements is false? (a) temperature is a state function (b) work is a state function (c) change in the state depends upon initial and final state (d) work appears at the boundary of the system

Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is (a) \(\Delta \mathrm{S}_{\text {sytem }}+\Delta \mathrm{S}_{\text {sarouedimgs }}>0\) (b) \(\Delta \mathrm{S}_{\text {system }}-\Delta \mathrm{S}_{\text {samondings }}>0\) (c) \(\Delta \mathrm{S}_{\text {sytem }}>0\) (d) \(\Delta S_{\text {surmundings }}>0\)

For which of the following processes will the entropy increase? (a) reaction of magnesium with oxygen to form magnesium oxide (b) reaction of nitrogen and hydrogen to form ammonia (c) sublimation of dry ice (d) condensation of steam

Which of the following is correct equation? (a) \(\Delta U=\Delta Q-W\) (b) \(\Delta \mathrm{W}=\Delta \mathrm{U}+\Delta \mathrm{Q}\) (c) \(\Delta \mathrm{U}=\Delta \mathrm{W}+\Delta \mathrm{Q}\) (d) none of these

Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction? (a) exothermic and increasing disorder (b) exothermic and decreasing disorder (c) endothermic and increasing disorder (d) endothermic and decreasing disorder

Identify the correct statement for change of Gibbs energy for a system \(\left(\Delta \mathrm{G}_{\text {gysem }}\right)\) at constant temperature and pressure: (a) if \(\Delta \mathrm{G}_{\text {system }}=0\), the system is still moving in a particular direction (b) if \(\Delta \mathrm{G}_{\text {systen }}=-\mathrm{ve}\), the process is not spontaneous (c) if \(\Delta \mathrm{G}_{\text {sysem }}=+\mathrm{ve}\), the process is spontaneous (d) if \(\Delta \mathrm{G}_{\text {sysem }}=0\), the system has attained equilibrium

Assume each reaction is carried out in an open container. For which reaction \(\Delta \mathrm{H}=\Delta \mathrm{U}\) ? (a) \(\mathrm{PCl}_{5}(\mathrm{~g}) \longrightarrow \mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})\) (b) \(2 \mathrm{CO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{CO}_{2}(\mathrm{~g})\) (c) \(\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Br}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{HBr}(\mathrm{g})\) (d) \(\mathrm{C}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \longrightarrow 2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{CO}_{2}(\mathrm{~g})\)

Identify the correct statement regarding entropy. (a) at absolute zero temperature, entropy of a perfectly crystalline substance is +ve. (b) at absolute zero temperature, entropy of a perfectly crystalline substance is taken to be zero (c) at absolute zero temperature, entropy of all crystalline substances in taken to be 0 . (d) at \(0^{\circ} \mathrm{C}\), entropy of a perfectly crystalline substance is taken to be 0 .

Standard molar enthalpy of formation of \(\mathrm{CO}_{2}\) is equal to (a) standard molar enthalpy of combustion of carbon (graphite) (b) standard molar enthalpy of combustion of gaseous carbon (c) sum of standard molar enthalpies of formation of \(\mathrm{CO}\) and \(\mathrm{O}_{2}\) (d) zero

Which one of the following has \(\Delta S^{\circ}\) greater than zero? (a) \(\mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{CaCO}_{3}(\mathrm{~g})\) (b) \(\mathrm{NaCl}(\mathrm{aq}) \rightleftharpoons \mathrm{NaCl}(\mathrm{s})\) (c) \(\mathrm{NaNO}_{3}(\mathrm{~s}) \rightleftharpoons \mathrm{Na}^{+}(\mathrm{aq})+\mathrm{NO}_{3}^{-}(\mathrm{aq})\) (d) \(\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g})\)

For a spontaneous process, the correct statement is (a) entropy of the system always increases (b) free energy of the system always increases (c) total entropy change is always negative (d) total entropy change is always positive

Which of the following is not an endothermic reaction? (a) combustion of methane (b) decomposition of water (c) dehydrogenation of ethane or ethylene (d) conversion of graphite to diamond

Which of the following statements is false? (a) work is a state function (b) temperature is a state function (c) change of state is completely denned when initial and final states are specified. (d) work appears at the boundary of the solution.

Classify each of the following processes as spontaneous or non-spontaneous. I. \(\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{g}), \mathrm{T}=25^{\circ} \mathrm{C}\) vessel open to atomsphere with \(50 \%\) relative humidity. II. \(\mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{l}), \mathrm{T}=25^{\circ} \mathrm{C}, \mathrm{P}=1 \mathrm{~atm}\) (a) I and II are both non-spontaneous (b) I and II are both spontaneous (c) I is non-spontaneous and II is spontaneous (d) I is spontaneous and II is non-spontaneous

The Gibbs free energy is defined as (a) \(\mathrm{G}=\mathrm{H}-\mathrm{T} \cdot \mathrm{S}\) (b) \(\mathrm{G}=\mathrm{H}+\mathrm{T} \cdot \mathrm{S}\) (c) \(\mathrm{G}=\mathrm{E}-\mathrm{T} \cdot \mathrm{S}\) (d) \(\mathrm{G}=\mathrm{E}+\mathrm{T} \cdot \mathrm{S}\)

Which of the following statement is true for \(\Delta \mathrm{G}\) ? (a) it is always proportional to \(\Delta \mathrm{H}\) (b) it may be less than or greater than or equal to \(\Delta H\) (c) it is always greater than \(\Delta \mathrm{H}\) (d) it is always less than \(\Delta \mathrm{H}\)

The free energy change \(\left(\Delta G^{\circ}\right)\) is negative when (a) the surroundings do no electrical work on the system (b) the suiroundings do electrical work on the system (c) the system does electrical work on the surroundings (d) the system does no electrical work on the surroundings

In a constant volume calorimeter \(3.5 \mathrm{~g}\) of a gas (mol.wt.28) was burnt in excess \(\mathrm{O}_{2}\) at \(298 \mathrm{~K}\). The increase in temperature is \(0.45 \mathrm{~K}\) due to combustion. If Heat capacity of calorimeter is \(2.5 \mathrm{~K} 5 / \mathrm{K}\) the value of \(\Delta E\) is (a) \(90 \mathrm{~kJ} / \mathrm{m}\) (b) \(9 \mathrm{~kJ} / \mathrm{m}\) (c) \(45 \mathrm{~kJ} / \mathrm{m}\) (d) \(18 \mathrm{~kJ} / \mathrm{m}\)

The amount of heat required to raise the temperature of one mole of the substance through \(1 \mathrm{~K}\) is called, its (a) molar heat (b) entropy (c) thermal capacity (d) specific heat

Bond energy of \(\mathrm{N}-\mathrm{H}, \mathrm{H}-\mathrm{H}\), and \(\mathrm{N} \equiv \mathrm{N}\) bonds are \(\mathrm{Q}_{1}\), \(\mathrm{Q}_{2}\) and \(\mathrm{Q}_{3} ; \Delta \mathrm{H}\) of \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \longrightarrow 2 \mathrm{NH}_{3}\) is (a) \(\mathrm{Q}_{3}+3 \mathrm{Q}_{2}-2 \mathrm{Q}_{1}\) (b) \(2 Q_{1}-Q_{3}-2 Q_{2}\) (c) \(\mathrm{Q}_{3}+3 \mathrm{Q}_{2}-6 \mathrm{Q}_{1}\) (d) \(\mathrm{Q}_{1}+\mathrm{Q}_{2}-\mathrm{Q}_{3}\)

Which of the following gas molecule has the maxi mum specific heat at constant pressure? (a) helium (b) argon (c) nitrogen (d) oxygen

A reaction occurs spontaneously if (a) \(\mathrm{T} \Delta \mathrm{S}<\Delta \mathrm{H}\) and both \(\Delta \mathrm{H}, \Delta \mathrm{S}\) are \(+\mathrm{ve}\) (b) \(\mathrm{T} \Delta \mathrm{S}>\Delta \mathrm{H}\) and \(\Delta \mathrm{H}=+\mathrm{ve}, \Delta \mathrm{S}=-\mathrm{ve}\) (c) \(\mathrm{T} \Delta \mathrm{S}>\Delta \mathrm{H}\) and both \(\Delta \mathrm{H}, \Delta \mathrm{S}\) are \(+\mathrm{ve}\) (d) \(\mathrm{T} \Delta \mathrm{S}=\Delta \mathrm{H}\) and both \(\Delta \mathrm{H}, \Delta \mathrm{S}\) are \(+\mathrm{ve}\)

For the reaction of one mole of \(\mathrm{Zn}\) dust with one mole of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in a bomb calorimeter, \(\Delta \mathrm{U}\) and \(\mathrm{w}\) corresponds to (a) \(\Delta \mathrm{U}<0, \mathrm{w}=0\) (b) \(\Delta \mathrm{U}<0, \mathrm{w}<0\) (c) \(\Delta \mathrm{U}>0, \mathrm{w}=0\) (d) \(\Delta \mathrm{U}>0, \mathrm{w}>0\)

Standard enthalpy and standard entropy changes for the oxidation of ammonia at \(298 \mathrm{~K}\) are \(-382.64 \mathrm{~kJ}\) \(\mathrm{mol}^{-1}\) and \(-145.6 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\), respectively. Standard Gibbs energy change for the same reaction at \(268 \mathrm{~K}\) is (a) \(-221.1 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(-339.3 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(-439.3 \mathrm{kJmol}^{-1}\) (d) \(-523.2 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

The molar heat capacity of water at constant pressure, C , is \(75 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\). When \(1.0 \mathrm{~kJ}\) of heat is supplied to \(100 \mathrm{~g}\) of water which is free to expand, the increase in temperature of water is (a) \(4.8 \mathrm{~K}\) (b) \(6.6 \mathrm{~K}\) (c) \(1.2 \mathrm{~K}\) (d) \(2.4 \mathrm{~K}\)

What is the entropy change (in \(\mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) ) when \(1 \mathrm{~mol}\) of ice is converted into water at \(0^{\circ} \mathrm{C}\) ? (The enthalpy change for the conversion of ice to liquid water is \(6.0\) \(\mathrm{kJ} \mathrm{mol}^{-1}\) at \(\left.0^{\circ} \mathrm{C}\right)\) (a) \(2.198\) (b) \(21.98\) (c) \(20.13\) (d) \(2.013\)

For the reaction, \(\mathrm{C}_{3} \mathrm{H}_{8}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 3 \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}\) (I) at constant temperature, \(\Delta \mathrm{H}-\Delta \mathrm{E}\) is (a) \(+3 \mathrm{RT}\) (b) \(-\mathrm{RT}\) (c) \(+\mathrm{RT}\) (d) \(-3 \mathrm{RT}\)

2 mole of an ideal gas at \(27^{\circ} \mathrm{C}\) temperature is expanded reversibly from \(2 \mathrm{~L}\) to \(20 \mathrm{~L}\). Find entropy change in cal. \((\mathrm{R}=2 \mathrm{cal} / \mathrm{mol} \mathrm{K})\) (a) \(92.1\) (b) 0 (c) 4 (d) \(9.2\)

When 1 mole gas is heated at constant volume tem perature is raised from 298 to \(308 \mathrm{~K}\). Heat supplied to the gas is \(500 \mathrm{~J}\). Then which of the following state ments is correct? (a) \(\mathrm{Q}=\mathrm{W}=500 \mathrm{~J}, \Delta \mathrm{U}=0\) (b) \(\mathrm{Q}=\Delta \mathrm{U}=500 \mathrm{~J}, \mathrm{~W}=0\) (c) \(\mathrm{Q}=\mathrm{W}=500 \mathrm{~J}, \Delta \mathrm{U}=0\) (d) \(\Delta \mathrm{U}=0, \mathrm{Q}=\mathrm{W}=-500 \mathrm{~J}\)

The entropy change in the fusion of 1 mol of a solid melting at \(27^{\circ} \mathrm{C}\) (Latent heat of fusion, \(2930 \mathrm{~J} \mathrm{~mol}^{-1}\) ) is (a) \(9.77 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) (b) \(10.73 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) (c) \(2930 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) (d) \(108.5 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\)

The factor of \(\Delta \mathrm{G}\) values is important in metallurgy. The \(\Delta\) G values for the following reactions at \(800^{\circ} \mathrm{C}\) are given as \(\mathrm{S}_{2}(\mathrm{~s})+2 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{SO}_{2}(\mathrm{~g}) ; \Delta \mathrm{G}=-544 \mathrm{~kJ}\) \(2 \mathrm{Zn}(\mathrm{s})+\mathrm{S}_{2}(\mathrm{~s}) \longrightarrow 2 \mathrm{ZnS}(\mathrm{s}) ; \Delta \mathrm{G}=-293 \mathrm{~kJ}\) \(2 \mathrm{Zn}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{ZnO}(\mathrm{s}) ; \Delta \mathrm{G}=-480 \mathrm{~kJ}\) the \(\Delta \mathrm{G}\) for the reaction, \(2 \mathrm{ZnS}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{ZnO}(\mathrm{s})+2 \mathrm{SO}_{2}(\mathrm{~g})\) will be (a) \(-357 \mathrm{~kJ}\) (b) \(-731 \mathrm{~kJ}\) (c) \(-773 \mathrm{~kJ}\) (d) \(-229 \mathrm{~kJ}\)

1 mole of an ideal gas at \(300 \mathrm{~K}\) is expanded isothermally and reversible from an initial volume of 1 litre to 10 litre. The work in this process is \(\left(\mathrm{R}=2 \mathrm{cal} \mathrm{mol}^{-1} \mathrm{~K}^{-1}\right)\) (a) \(163.7 \mathrm{cal}\) (b) zero (c) \(-1381.8 \mathrm{cal}\) (d) 9 litreatm

Standard state Gibbs free energy change for isomerization reaction, cis-2-pentene \rightleftharpoons- trans-2-pentene is \(-3.67 \mathrm{~kJ} / \mathrm{mol}\) at \(400 \mathrm{~K}\). if more trans-2-pentene is added to the reaction vessel, then (a) more cis-2-pentene is formed (b) additional trans-2-pentene is formed (c) equilibrium remains unaffected (d) equilibrium is shifted in the forward direction

A diatomic ideal gas is used in a carnot engine as the working substance. If during the adiatotic expansion part of the cycle the volume of the gas increases from \(\mathrm{V}\) to \(32 \mathrm{~V}\) the efficiency of the engine is (a) \(0.75\) (b) \(0.25\) (c) \(0.5\) (d) \(0.8\)

The enthalpy and entropy change for a chemical reaction are \(-2.5 \times 10^{3} \mathrm{~J} \mathrm{~mol}^{-1}\) and \(7.4 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) respec- tively. The reaction at \(298 \mathrm{~K}\). is (a) non-spontaneous (b) spontaneous (c) reversible (d) irreversible

The enthalpy and entropy change for the reaction \(\mathrm{Br}_{2}(1)+\mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{BrCl}(\mathrm{g})\) are \(30 \mathrm{~kJ} \mathrm{~mol}^{-1}\) and \(105 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\) respectively. The temperature at which the reaction will be in equilibrium is (a) \(450 \mathrm{~K}\) (b) \(300 \mathrm{~K}\) (c) \(285.7 \mathrm{~K}\) (d) \(273 \mathrm{~K}\)

The enthalpy of hydrogenation of cyclohexene is \(-119.5\) \(\mathrm{kJ} \mathrm{mol}^{-1}\). If resonance energy of benzene is \(-150.4 \mathrm{~kJ}\) \(\mathrm{mol}^{-1}\), its enthalpy of hydrogenation would be (a) \(-269.9 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(-358.5 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(-508.9 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(-208.1 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

The work done by a system is 10 joule, when 40 joule heat is supplied to it. What is the increase in internal energy of system? (a) \(30 \mathrm{~J}\) (b) \(50 \mathrm{~J}\) (c) \(40 \mathrm{~J}\) (d) \(20 \mathrm{~J}\)

For a reaction at \(300 \mathrm{~K}\), enthalpy and entropy changes are \(-11.5 \times 10^{3} \mathrm{~J} \mathrm{~mol}^{-1}\) and \(-105 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\) respec- tively. What is the change in Gibbs free energy? (a) \(25 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(30 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(15 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(20 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

The standard enthalpy of decomposition of \(\mathrm{N}_{2} \mathrm{O}_{4}\) to \(\mathrm{NO}_{2}\) is \(58.04 \mathrm{~kJ}\) and standard entropy of this reaction is \(176.7 \mathrm{~J} \mathrm{~K}^{-1}\). The standard free energy change for this reaction at \(25^{\circ} \mathrm{C}\), is (a) \(5.39 \mathrm{~kJ}\) (b) \(-5.39 \mathrm{~kJ}\) (c) \(539 \mathrm{~kJ}\) (d) \(53.9 \mathrm{~kJ}\)