Chemical Thermodynamics · JEE Main previous year questions

If the standard molar enthalpy change for combustion of graphite powder is $-2.48\times 10^2\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$, the amount of heat generated on combustion of 1 g of graphite powder is ____ kJ. (Nearest integer)

For the reaction ${\mathrm{C}}_2{\mathrm{H}}_6\to {\mathrm{C}}_2{\mathrm{H}}_4+{\mathrm{H}}_2$ the reaction enthalpy ${\Delta }_{\mathrm{r}}\mathrm{H}=$ ____ $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. (Round off to the Nearest Integer). [ Given : Bond enthalpies in $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}:\mathrm{C}\text{-}\mathrm{C}:347,\mathrm{C}=\mathrm{C}:611;\mathrm{C}\text{-}\mathrm{H}:414,\mathrm{H}\text{-}\mathrm{H}:436\text{ ]}$

For the reaction $2\mathrm{F}{\mathrm{e}}^{3+}(\mathrm{aq})+2{\mathrm{I}}^{-}(\mathrm{aq})\to 2\mathrm{F}{\mathrm{e}}^{2+}(\mathrm{aq})+{\mathrm{I}}_2(\mathrm{s})$ the magnitude of the standard molar Gibbs free energy change, ${\Delta }_{\mathrm{r}}{\mathrm{G}}_m^o=-$ ____ kJ (Round off to the Nearest Integer). $$\left[\begin{array}{cc}{E}_{\mathrm{F}{\mathrm{e}}^{2+}/Fe(\mathrm{s})}^o=-0.440\mathrm{V};& E_{\mathrm{F}{\mathrm{e}}^{3+}/Fe(\mathrm{s})}^o=-0.036\mathrm{V}\\ E_{{\mathrm{I}}_2/2{\mathrm{I}}^{-}}^o=0.539\mathrm{V};& F=96500C\end{array}\right]$$

For a chemical reaction $\mathrm{A}+\mathrm{B}\rightleftharpoons \mathrm{C}+\mathrm{D}$ $({\Delta }_r{H}^{\ominus }=80\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1})$ the entropy change ${\Delta }_r{S}^{\ominus }$ depends on the temperature T (in K) as ${\Delta }_r{S}^{\ominus }=2\mathrm{T}(\mathrm{J}{\mathrm{K}}^{-1}\mathrm{mo}{\mathrm{l}}^{-1})$. Minimum temperature at which it will become spontaneous is _________ K. (Integer)

The correct order of electron gain enthalpy is :

1. A.Te > Se > S > O
2. B.S > Se > Te > O
3. C.S > O > Se > Te
4. D.O > S > Se > Te

The average S-F bond energy in $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ of $\mathrm{S}{\mathrm{F}}_6$ is _________. (Rounded off to the nearest integer) [Given : The values of standard enthalpy of formation of $\mathrm{S}{\mathrm{F}}_6(\mathrm{g})$, S(g) and F(g) are - 1100, 275 and 80 $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ respectively.]

The correct order of bond dissociation enthalpy of halogens is :

1. A.${\mathrm{F}}_2>\mathrm{C}{\mathrm{l}}_2>\mathrm{B}{\mathrm{r}}_2>{\mathrm{I}}_2$
2. B.$\mathrm{C}{\mathrm{l}}_2>\mathrm{B}{\mathrm{r}}_2>{\mathrm{F}}_2>{\mathrm{I}}_2$
3. C.${\mathrm{I}}_2>\mathrm{B}{\mathrm{r}}_2>\mathrm{C}{\mathrm{l}}_2>{\mathrm{F}}_2$
4. D.$\mathrm{C}{\mathrm{l}}_2>{\mathrm{F}}_2>\mathrm{B}{\mathrm{r}}_2>{\mathrm{I}}_2$

For the given cell : $$\mathrm{Cu}(\mathrm{s})\mid \mathrm{C}{\mathrm{u}}^{2+}({\mathrm{C}}_1\mathrm{M})\parallel \mathrm{C}{\mathrm{u}}^{2+}({\mathrm{C}}_2\mathrm{M})\mid \mathrm{Cu}(\mathrm{s})$$ change in Gibbs energy ($\Delta G$) is negative, if :

1. A.$C_2=\sqrt{2}{C}_1$
2. B.$C_2=\frac{C_1}{\sqrt{2}}$
3. C.$C_1=2C_2$
4. D.$C_1=C_2$

The Gibbs change (in J) for the given reaction at $[\mathrm{C}{\mathrm{u}}^{2+}]=[\mathrm{S}{\mathrm{n}}^{2+}]=1\mathrm{M}$ and $298\mathrm{K}$ is : $\mathrm{Cu}(\mathrm{s})+\mathrm{S}{\mathrm{n}}^{2+}(aq.)\to \mathrm{C}{\mathrm{u}}^{2+}(aq.)+\mathrm{Sn}(\mathrm{s})$; $(E_{\mathrm{S}{\mathrm{n}}^{2+}|Sn}^0=-0.16\mathrm{V},$ $E_{\mathrm{C}{\mathrm{u}}^{2+}|Cu}^0=0.34\mathrm{V})$ Take $\mathrm{F}=96500\mathrm{C}\mathrm{mo}{\mathrm{l}}^{-1})$

The heat of combustion of ethanol into carbon dioxide and water is $-327\mathrm{kcal}$ at constant pressure. The heat evolved (in cal) at constant volume and $27^{\circ }\mathrm{C}$ (if all gases behave ideally) is ($\mathrm{R}=2\mathrm{cal}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-1}$) _______.

1. A.(b) < (c) < (a)
2. B.(a) < (c) < (b)
3. C.(a) < (b) < (c)
4. D.(c) < (b) < (a)

The third ionization enthalpy is minimum for :

1. A.Ni
2. B.Co
3. C.Mn
4. D.Fe

For the following Assertion and Reason, the correct option is : Assertion : The pH of water increases with increase in temperature. Reason : The dissociation of water into ${\mathrm{H}}^{+}$ and ${\mathrm{OH}}^{-}$ is an exothermic reaction.

1. A.Both assertion and reason are false.
2. B.Both assertion and reason are true, but the reason is not the correct explanation for the assertion.
3. C.Both assertion and reason are true, and the reason is the correct explanation for the assertion.
4. D.Assertion is not true, but reason is true.

The standard heat of formation $({\Delta }_f{H}_{298}^{\circ })$ of ethane (in kJ/mol), if the heat of combustion of ethane, hydrogen and graphite are - 1560, -393.5 and -286 kJ/mol, respectively is :

Enthalpy of sublimation of iodine is $24{\text{ cal g}}^{-1}$ at $200{}^{\circ }\text{C}$. If specific heat of ${\text{I}}_2\text{(s)}$ and ${\text{I}}_2\text{ (vap)}$ are 0.055 and $0.031{\text{ cal g}}^{-1}{\text{K}}^{-1}$ respectively, then enthalpy of sublimation of iodine at $250{}^{\circ }\text{C}$ in ${\text{cal g}}^{-1}$ is :

1. A.2.85
2. B.22.8
3. C.11.4
4. D.5.7

A process will be spontaneous at all temperatures if :

1. A.$\Delta \mathrm{H}<0$ and $\Delta \mathrm{S}>0$
2. B.$\Delta \mathrm{H}<0$ and $\Delta \mathrm{S}<0$
3. C.$\Delta \mathrm{H}>0$ and $\Delta \mathrm{S}<0$
4. D.$\Delta \mathrm{H}>0$ and $\Delta \mathrm{S}>0$

1. A.Formation of A and B from C has highest enthalpy of activation.
2. B.D is kinetically stable product.
3. C.C is the thermodynamically stable product
4. D.Activation enthalpy to form C is $5\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ less than that to form D.

Given (i) $\mathrm{C}(\mathrm{graphite})+{\mathrm{O}}_2(\mathrm{g})\to \mathrm{C}{\mathrm{O}}_2(\mathrm{g})$; ${\Delta }_r{H}^{\ominus }=x\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ (ii) $\mathrm{C}(\mathrm{graphite})+\frac{1}{2}{\mathrm{O}}_2(\mathrm{g})\to \mathrm{CO}(\mathrm{g})$; ${\Delta }_r{H}^{\ominus }=y\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ (iii) $\mathrm{CO}(\mathrm{g})+\frac{1}{2}{\mathrm{O}}_2(\mathrm{g})\to \mathrm{C}{\mathrm{O}}_2(\mathrm{g})$; ${\Delta }_r{H}^{\ominus }=z\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?

1. A.z = x + y
2. B.x = y + z
3. C.x = y − z
4. D.y = 2z − x

The standard reaction Gibbs energy for a chemical reaction at an absolute temperature T is given by $${\Delta }_{\mathrm{r}}{\mathrm{G}}^{\circ }=\mathrm{A}-\mathrm{BT}$$ Where A and B are non-zero constants. Which of the following is TRUE about this reaction?

1. A.Exothermic if $\mathrm{B}<0$
2. B.Endothermic if $\mathrm{A}>0$
3. C.Exothermic if $\mathrm{A}>0$ and $\mathrm{B}<0$
4. D.Endothermic if $\mathrm{A}<0$ and $\mathrm{B}>0$

1. A.
2. B.
3. C.
4. D.

The gas phase reaction $2\mathrm{N}{\mathrm{O}}_2(\mathrm{g})\to {\mathrm{N}}_2{\mathrm{O}}_4(\mathrm{g})$ is an exothermic reaction. The decomposition of ${\mathrm{N}}_2{\mathrm{O}}_4$, in equilibrium mixture of $\mathrm{N}{\mathrm{O}}_2(\mathrm{g})$ and ${\mathrm{N}}_2{\mathrm{O}}_4(\mathrm{g})$, can be increased by :

1. A.lowering the temperature.
2. B.increasing the pressure.
3. C.addition of an inert gas at constant volume.
4. D.addition of an inert gas at constant pressure.

1. A.A and D
2. B.A and B
3. C.B and C
4. D.C and D

The combustion of benzene(l) gives ${\text{CO}}_2(\text{g})$ and ${\text{H}}_2\text{O}(\text{l})$. Given that heat of combustion of benzene at constant volume is $-3263.9\text{kJ}{\text{mol}}^{-1}$ at $25^{\circ }\text{C}$; heat of combustion (in $\text{kJ}{\text{mol}}^{-1}$) of benzene at constant pressure will be : $(\text{R}=8.314\text{J}{\text{K}}^{-1}{\text{mol}}^{-1})$

1. A.$-3267.6$
2. B.4152.6
3. C.$-452.46$
4. D.3260

A gas undergoes change from state A to state B. In this process, the heat absorbed and work done by the gas is 5 J and 8 J, respectively. Now gas is brought back to A by another process during which 3 J of heat is evolved. In this reverse process of B to A :

1. A.10 J of the work will be done by the gas.
2. B.6 J of the work will be done by the gas.
3. C.10 J of the work will be done by the surrounding on gas.
4. D.6 J of the work will be done by the surrounding on gas.