Chapter 6

The bond energy of an \(\mathrm{O}-\mathrm{H}\) bond is \(109 \mathrm{kcal} \mathrm{mol}^{-1} .\) When \(5 \times 10^{-3}\) mole of water is formed, the energy released in kcals is approximately

For the reaction, \(\mathrm{Ag}_{2} \mathrm{O}(\mathrm{s}) \rightleftharpoons 2 \mathrm{Ag}(\mathrm{s})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g})\) \(\Delta \mathrm{H}, \Delta \mathrm{S}\) and \(\mathrm{T}\) are \(40.657 \mathrm{~kJ} \mathrm{~mol}^{-1}, 109 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\) and \(373 \mathrm{~K}\) respectively. Find the free energy change \((\Delta \mathrm{G})\) of the reaction.

Heat required to raise the temperature of \(1 \mathrm{~mol}\) of a substance by \(1^{\circ}\) is called (a) specific heat (b) molar heat capacity (c) water equivalent (d) specific gravity

A heat engine absorbs heat \(Q_{1}\) from a source at tem perature \(\mathrm{T}_{1}\) and heat \(\mathrm{Q}_{2}\) from a source at temperature \(\mathrm{T}_{2} .\) Work done is found to be \(\mathrm{J}\left(\mathrm{Q}_{1}+\mathrm{Q}_{2}\right)\). This is in accordance with: (a) first law of thermodynamics (b) second law of thermodynamics (c) joules equivalent law (d) none of these

The correct relationship between free energy change in a reaction and the corresponding equilibrium constant \(K_{c}\) is \([\mathbf{2 0 0 3}]\) (a) \(\Delta \mathrm{G}=\mathrm{RT} \operatorname{In} \mathrm{K}\) (b) \(-\Delta \mathrm{G}=\mathrm{RT} \operatorname{In} \mathrm{K}\) (c) \(\Delta G^{\circ}=R T\) In \(K\) (d) \(-\Delta G^{\circ}=\mathrm{RT} \operatorname{In} \mathrm{K}_{\mathrm{c}}\)

If at \(298 \mathrm{~K}\) the bond energies of \(\mathrm{C}-\mathrm{H}, \mathrm{C}-\mathrm{C}, \mathrm{C}=\mathrm{C}\) and \(\mathrm{H}-\mathrm{H}\) bonds are respectively \(414,347,615\) and \(435 \mathrm{~kJ} \mathrm{~mol}^{-1}\), the value of enthalpy change for the reaction \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{3}(\mathrm{~g})\) at \(298 \mathrm{~K}\) will be (a) \(+250 \mathrm{~kJ}\) (b) \(-250 \mathrm{~kJ}\) (c) \(+125 \mathrm{~kJ}\) (d) \(-125 \mathrm{~kJ}\)

The enthalpy change for a reaction does not depend upon the (a) physical state of reactants and products (b) use of different reactants for the same product (c) nature of intermediate reaction steps (d) difference in initial or final temperatures of in volved substances

In an irreversible process taking place at constant \(\mathrm{T}\) and \(\mathrm{P}\) and in which only pressure-volume work is being done, the change in Gibbs free energy \((\mathrm{dG})\) and change in entropy (dS), satisfy the criteria: [2003] (a) \((\mathrm{dS})_{\mathrm{V}, \mathrm{E}}<0,(\mathrm{dG})_{\mathrm{T}, \mathrm{P}}<0\) (b) \((\mathrm{dS})_{\mathrm{V} \mathbb{E}}>0,(\mathrm{dG})_{\mathrm{T}, \mathbb{P}}<0\) (c) \((\mathrm{dS})_{\mathrm{V}, \mathrm{E}}=0,(\mathrm{dG})_{\mathrm{T}, \mathrm{P}}=0\) (d) \((\mathrm{dS})_{\mathrm{VE}}=0,(\mathrm{dG})_{\mathrm{U}, \mathrm{p}}>0\)

The internal energy change when a system goes from state \(\mathrm{A}\) to \(\mathrm{B}\) is \(40 \mathrm{~kJ} / \mathrm{mol}\). If the system goes from \(\mathrm{A}\) to \(\mathrm{B}\) by a reversible path and returns to state A by an irreversible path what would be the net change in internal energy? [2003] (a) \(40 \mathrm{~kJ}\) (b) \(>40 \mathrm{~kJ}\) (c) \(<40 \mathrm{~kJ}\) (d) zero

An ideal gas expands in volume from \(1 \times 10^{-3} \mathrm{~m}^{3}\) to 1 \(\times 10^{-2} \mathrm{~m}^{3}\) at \(300 \mathrm{~K}\) against a constant pressure of \(1 \times\) \(10^{5} \mathrm{Nm}^{-2}\). The work done is (a) \(-900 \mathrm{k} \mathrm{J}\) (b) \(-900 \mathrm{~J}\) (c) \(270 \mathrm{~kJ}\) (d) \(940 \mathrm{~kJ}\)

The enthalpies of combustion of carbon and carbon monoxide are \(-393.5\) and \(-283 \mathrm{~kJ} \mathrm{~mol}^{-1}\) respectively. The enthalpy of formation of carbon monoxide per mole is (a) \(-676.5 \mathrm{~kJ}\) (b) \(-110.5 \mathrm{~kJ}\) (c) \(110.5 \mathrm{~kJ}\) (d) \(676.5 \mathrm{~kJ}\)

If the bond dissociation energies of \(\mathrm{XY}, \mathrm{X}_{2}\) and \(\mathrm{Y}_{2}\) are in the ratio of \(1: 1: 0.5\) and \(\Delta \mathrm{H}_{f}\) for the formation of \(\mathrm{XY}\) is \(-200 \mathrm{~kJ} / \mathrm{mole}\). The bond dissociation energy of \(\mathrm{X}_{2}\) will be ? [2005] (a) \(100 \mathrm{~kJ} / \mathrm{mole}\) (b) \(400 \mathrm{~kJ} / \mathrm{mole}\) (c) \(600 \mathrm{~kJ} / \mathrm{mole}\) (d) \(800 \mathrm{~kJ} / \mathrm{mole}\)

Consider the reaction \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightleftharpoons 2 \mathrm{NH}_{3}\) carried out at constant temperature and pressure. If \(\Delta \mathrm{H}\) and \(\Delta U\) are the enthalpy and internal energy changes for the reaction, which of the following expressions is true? (a) \(\Delta \mathrm{H}=0\) (b) \(\Delta \mathrm{H}=\Delta \mathrm{U}\) (c) \(\Delta \mathrm{H}<\Delta \mathrm{U}\) (d) \(\Delta \mathrm{H}>\Delta \mathrm{U}\)

An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If \(\mathrm{T}_{i}\) is the initial temperature and \(\mathrm{T}_{f}\) is the final temperature, which of the following statements is correct? [2006] (a) \(\left(\mathrm{T}_{\mathrm{f}}\right)_{\text {imev }}>\left(\mathrm{T}_{i}\right)_{\text {rev }}\) (b) \(\mathrm{T}_{\mathrm{f}}>\mathrm{T}_{1}\) for reversible process but \(\mathrm{T}_{\mathrm{f}}=\mathrm{T}_{1}\) for irreversible process (c) \(\left(T_{f}\right)_{\text {imev }}=\left(T_{i}\right)_{\text {rev }}\) (d) \(\mathrm{T}_{\mathrm{f}}=\mathrm{T}_{\mathrm{i}}\) for both reversible and irreversible processes

The enthalpy changes for the following processes are listed below. \(\mathrm{Cl}_{2}(\mathrm{~g})=2 \mathrm{Cl}(\mathrm{g}) ; 242.3 \mathrm{~kJ} \mathrm{~mol}^{-1}\) \(\mathrm{I}_{2}(\mathrm{~g})=21(\mathrm{~g}) ; 151.0 \mathrm{kJmol}^{-1}\) \(\mathrm{ICl}(\mathrm{g})=\mathrm{I}(\mathrm{g})+\mathrm{Cl}(\mathrm{g}) ; 211.3 \mathrm{~kJ} \mathrm{~mol}^{-1}\) \(\mathrm{I}_{2}(\mathrm{~s})=\mathrm{I}_{2}(\mathrm{~g}) ; 62.76 \mathrm{~kJ} \mathrm{~mol}^{-1}\) Given that the standard states for iodine and chlorine are \(\mathrm{I}_{2}\) (s) and \(\mathrm{Cl},(\mathrm{g})\), the standard enthalpy of formation for ICl (g) is (a) \(-14.6 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(-16.8 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(+16.8 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(+244.8 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

Asuming that water vapour is an ideal gas, the internal energy change \((\Delta U)\) when \(1 \mathrm{~mol}\) of water is vapourized at 1 bar pressure and \(100^{\circ} \mathrm{C}\), (Given: Molar enthalpy of vaporization of water at 1 bar and \(373 \mathrm{~K}\) \(=41 \mathrm{~kJ} \mathrm{~mol}^{-1}\) and \(\left.\mathrm{R}=8.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\right)\) will be \(\quad\) [2007] (a) \(3.7904 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(37.904 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(41.00 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(4.100 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

Identify the correct statement regarding a spontaneous process. [2007] (a) Endothermic processes are never spontaneous (b) Exothermic process are always spontaneous (c) Lowering of energy in the reaction process is the only criterion for spontaneity (d) For a spontaneous process in an isolated system, the change in entropy is positive.

In the conversion of lime stone to lime, \(\mathrm{CaCO}_{3}(\mathrm{~s}) \longrightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g})\) The values of \(\Delta \mathrm{H}^{\circ}\) and \(\Delta \mathrm{S}^{\circ}\) are \(+179.1 \mathrm{~kJ} \mathrm{~mol}^{-1}\) and \(160.2 \mathrm{~J} / \mathrm{K}\) respectively at \(298 \mathrm{~K}\) and 1 bar. Assuming that \(\Delta \mathrm{H}^{\circ}\) and \(\Delta \mathrm{S}^{\circ}\) do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is [2007] (a) \(1200 \mathrm{~K}\) (b) \(845 \mathrm{~K}\) (c) \(1118 \mathrm{~K}\) (d) \(1008 \mathrm{~K}\)

Standard entropy of \(\mathrm{X}_{2}, \mathrm{Y}_{2}\) and \(\mathrm{XY}_{3}\) are 60,40 and 50 \(\mathrm{JK}^{-1} \mathrm{~mol}^{-1}\), respectively. For the reaction, \(1 / 2 \mathrm{X}_{2}+3 / 2 \mathrm{Y}_{2} \longrightarrow \mathrm{XY}_{3}, \Delta \mathrm{H}=-30 \mathrm{~kJ}\), to be at equilibrium, the temperature will be \([2008]\) (a) \(1250 \mathrm{~K}\) (b) \(500 \mathrm{~K}\) (c) \(750 \mathrm{~K}\) (d) \(1000 \mathrm{~K}\)

Oxidizing power of chlorine in aqueous solution can be determined by the parameters indicated below: \(1 / 2 \mathrm{Cl}_{2}(\mathrm{~g}) \stackrel{1 / 2 \Delta \mathrm{H}_{\mathrm{Diss}}}{\longrightarrow} \mathrm{Cl}(\mathrm{g}) \stackrel{\Delta_{\mathrm{eg}} \mathrm{H}^{-}}{\longrightarrow}\) \(\mathbf{1 7 4}\). \(\mathrm{Cl}^{-}(\mathrm{g}) \quad \stackrel{\Delta_{\mathrm{hyd}} \mathrm{H}}{\longrightarrow} \mathrm{Cl}^{-}(\mathrm{aq})\) The energy involved in the conversion of \(1 / 2 \mathrm{Cl}_{2}(\mathrm{~g})\) to \(\mathrm{Cl}^{-}(\mathrm{g})\) (Using the data, \(\Delta \mathrm{H}_{\mathrm{Cl}_{2}}=240 \mathrm{~kJ} \mathrm{~mol}^{-1}, \Delta_{\mathrm{cg}} \mathrm{H}^{-\mathrm{Cl}}=\) \(-349 \mathrm{~kJ} \mathrm{~mol}^{-1}, \Delta_{\mathrm{liyd}} \mathrm{H} \mathrm{Cl}=-381 \mathrm{~kJ} \mathrm{~mol}^{-\mathrm{i}}\) ) will be [2008] (a) \(+152 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(-610 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(-850 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(+120 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

Given: \(\mathrm{E}_{\mathrm{Fe} / \mathrm{Fe}}^{03+}=-0.036 \mathrm{~V}, \mathrm{E}_{\mathrm{Fe} \text { fe }}^{02+}=-0.439 \mathrm{~V}\). The value of standard electrode potential for the change, \(\mathrm{Fe}^{3+}(\mathrm{aq})\) \(+\mathrm{e}-\mathrm{Fe}^{2+}\) (aq) will be: \(\left.\quad \mathbf{[ 2 0 0 9}\right]\) (a) \(0.385 \mathrm{~V}\) (b) \(0.770 \mathrm{~V}\) (c) \(-0.270 \mathrm{~V}\) (d) \(-0.072 \mathrm{~V}\)

On the basis of the following thermochemical data: \(\left(\Delta \mathrm{G}^{\circ} \mathrm{H}+(\mathrm{aq})=0\right)\) \(\mathrm{H}_{2} \mathrm{O}(\mathrm{I}) \longrightarrow \mathrm{H}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})\) \(\Delta \mathrm{H}=57.32 \mathrm{~kJ}\) \(\mathrm{H}_{2}(\mathrm{~g})+1 / 2 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(1)\) \(\Delta \mathrm{H}=-286.20 \mathrm{~kJ}\) The value of enthalpy of formation of \(\mathrm{OH}^{-}\)ion at \(25^{\circ} \mathrm{C}\) is: \(\quad\) [2009] (a) \(-228.88 \mathrm{~kJ}\) (b) \(+228.88 \mathrm{~kJ}\) (c) \(-343.52 \mathrm{~kJ}\) (d) \(-22.88 \mathrm{~kJ}\)

The standard enthalpy of formation of \(\mathrm{NH}_{3}\) is \(-46.0\) \(\mathrm{kJ} \mathrm{mol}^{-1}\). If the enthalpy of formation of \(\mathrm{H}_{2}\) from its atoms is \(-436 \mathrm{~kJ} \mathrm{~mol}^{-1}\) and that of \(\mathrm{N}_{2}\) is \(-712 \mathrm{~kJ}\) \(\mathrm{mol}^{-1}\), the average bond enthalpy of \(\mathrm{N}-\mathrm{H}\) bond in \(\mathrm{NH}_{3}\) is \([\mathbf{2 0 1 0}]\) (a) \(-964 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (b) \(+352 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(+1056 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(-1102 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

The entropy change involved in the isothermal reversible expansion of 2 moles of an ideal gas from a volume of \(10 \mathrm{dm}^{3}\) to a volume of \(100 \mathrm{dm}^{3}\) at \(27^{\circ} \mathrm{C}\) is: (a) \(35.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\) (b) \(38.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\) (c) \(45.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\) (d) \(23.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\)

The incorrect expression among the following is \([2012]\) (a) \(\ln \mathrm{K}=\frac{\Delta \mathrm{H}^{\circ}-\mathrm{T} \Delta \mathrm{S}^{\circ}}{\mathrm{RT}}\) (b) In isothermal process \(\mathrm{W}_{\text {revesible }}=-\mathrm{nRT} \operatorname{In} \frac{\mathrm{V}_{\mathrm{f}}}{\mathrm{V}_{1}}\) (c) \(\frac{\Delta \mathrm{G}_{\text {sysem }}}{\Delta \mathrm{S}_{\text {loel }}}=-\mathrm{T}\) (d) \(\mathrm{K}=\mathrm{e}^{\Delta \mathrm{G}^{*} / \mathrm{RT}}\)

A piston filled with \(0.04 \mathrm{~mol}\) of an ideal gas expands reversibly from \(50.0 \mathrm{~mL}\) to \(375 \mathrm{~mL}\) at a constant temperature of \(37.0^{\circ} \mathrm{C}\). As it does so, it absorbs \(208 \mathrm{~J}\) of heat. The values of \(\mathrm{q}\) and \(\mathrm{w}\) for the process will be: \([2013]\) \((\mathrm{R}=3.314 \mathrm{~J} / \mathrm{mol} \mathrm{K})(\operatorname{Ln} 7.5=2.01)\) (a) \(\mathrm{q}=-208 \mathrm{~J}, \mathrm{w}=+208 \mathrm{~J}\) (b) \(\mathrm{q}=+208 \mathrm{~J}, \mathrm{w}=+208 \mathrm{~J}\) (c) \(\mathrm{q}=+208 \mathrm{~J}, \mathrm{w}=-208 \mathrm{~J}\) (d) \(\mathrm{q}=-208 \mathrm{~J}, \mathrm{w}=-208 \mathrm{~J}\)

For complete combustion of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \ell+1\) \(3 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{O} \ell\) the amount of heat pro- duced as measured in bomb calorimeter, is \(1364.47 \mathrm{~kJ}\) \(\mathrm{mol}^{-1}\) at \(25^{\circ} \mathrm{C}\). Assuming ideality the Enthalpy of combustion, \(\Delta_{\mathrm{c}} \mathrm{H}\) for the reaction will be: [2014] \(\left(\mathrm{R}=8.314 \mathrm{~kJ} \mathrm{~mol}^{-1}\right)\) (a) \(-1460.50 \mathrm{kj} \mathrm{mol}^{-1}\) (b) \(-1350.50 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (c) \(-1366.95 \mathrm{~kJ} \mathrm{~mol}^{-1}\) (d) \(-1361.95 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

The standard Gibbs energy change at \(300 \mathrm{~K}\) for the reaction \(2 \mathrm{~A}=\mathrm{B}+\mathrm{C}\) is \(2494.2 \mathrm{~J}\). At a given time, the composition of the reaction mixture is \(\mathrm{A}=\frac{1}{2}[\mathrm{~B}]=2\) and \([\mathrm{C}]=\frac{1}{2}\) The reaction proceeds in the : \([\mathrm{R}=8.314 \mathrm{~J} / \mathrm{K} / \mathrm{mol}, \mathrm{e}=2.718\) (a) Forward direction because \(\mathrm{Q}>\mathrm{K}_{\mathrm{C}}\) (b) Reverse direction because \(\mathrm{Q}>\mathrm{K}_{\mathrm{c}}\) (c) Forward direction because \(Q

The heats of combustion of carbon and carbon monoxide are \(-393.5\) and \(-283.5 \mathrm{~kJ} \mathrm{~mol}^{-1}\), respectively. The heat of formation (in \(\mathrm{kJ}\) ) of carbon monoxide per mole is: (a) \(676.5\) (b) \(-676.5\) (c) \(-110.5\) (d) \(110.5\)

At \(300 \mathrm{~K}\) and \(1 \mathrm{~atm}, 15 \mathrm{~mL}\) a gaseous hydrocarbon requires \(375 \mathrm{~mL}\) air containing \(20 \% \mathrm{O}_{2}\) by volume for complete combustion. After comustion the gases occupy \(330 \mathrm{~mL}\). Assuming that the water formed is in liquid form and the volumes were measured at the same temperature and pressure, the formula of the hydrocarbon is: (a) \(\mathrm{C}_{3} \mathrm{H}_{\mathrm{s}}\) (b) \(\mathrm{C}_{4} \mathrm{H}_{8}\) (c) \(\mathrm{C}_{4} \mathrm{H}_{10}\) (d) \(\mathrm{C}_{3} \mathrm{H}_{6}\)