Chemical Thermodynamics · JEE Main previous year questions

The effect of temperature on spontaneity of reactions are represented as : | | $\Delta \mathrm{H}$ | $\Delta \mathrm{S}$ | Temperature | Spontaneity | |---|---|---|---|---| | (A) | $+$ | $-$ | any T | Non spontaneous | | (B) | $+$ | $+$ | low T | spontaneous | | (C) | $-$ | $-$ | low T | Non spontaneous | | (D) | $-$ | $+$ | any T | spontaneous | The incorrect combinations are :

1. A.(A) and (C) only
2. B.(B) and (D) only
3. C.(A) and (D) only
4. D.(B) and (C) only

The bond dissociation enthalpy of ${\mathrm{X}}_2$ $\Delta {\mathrm{H}}_{\mathrm{bond}}^{\circ }$ calculated from the given data is ____ $\mathrm{kJmo}{\mathrm{l}}^{-1}$. (Nearest integer) ${\mathrm{M}}^{+}{\mathrm{X}}^{-}(\mathrm{s})\to {\mathrm{M}}^{+}(\mathrm{g})+{\mathrm{X}}^{-}(\mathrm{g})\mathrm{\Delta }{\mathrm{H}}_{\mathrm{lattice}}^{\circ }=800\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ $\mathrm{M}(\mathrm{s})\to \mathrm{M}(\mathrm{g})\mathrm{\Delta }{\mathrm{H}}_{\mathrm{sub}}^{\circ }=100\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ $\mathrm{M}(\mathrm{g})\to {\mathrm{M}}^{+}(\mathrm{g})+{\mathrm{e}}^{-}(\mathrm{g})\mathrm{\Delta }{\mathrm{H}}_{\mathrm{i}}^{\circ }=500\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ $\mathrm{X}(\mathrm{g})+{\mathrm{e}}^{-}(\mathrm{g})\to {\mathrm{X}}^{-}(\mathrm{g})\mathrm{\Delta }{\mathrm{H}}_{\mathrm{eg}}^{\circ }=-300\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ $\mathrm{M}(\mathrm{s})+\frac{1}{2}{\mathrm{X}}_2(\mathrm{g})\to {\mathrm{M}}^{+}{\mathrm{X}}^{-}(\mathrm{s})\mathrm{\Delta }{\mathrm{H}}_{\mathrm{f}}^{\circ }=-400\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ [Given : ${\mathrm{M}}^{+}{\mathrm{X}}^{-}$ is a pure ionic compound and $\mathrm{X}$ forms a diatomic molecule ${\mathrm{X}}_2$ in gaseous state]

Given below are two statements : Statement (I) : The oxidation state of an element in a particular compound is the charge acquired by its atom on the basis of electron gain enthalpy consideration from other atoms in the molecule. Statement (II) : $\mathrm{p}\pi -\mathrm{p}\pi$ bond formation is more prevalent in second period elements over other periods. In the light of the above statements, choose the most appropriate answer from the options given below :

1. A.Statement I is correct but Statement II is incorrect
2. B.Both Statement I and Statement II are correct
3. C.Statement I is incorrect but Statement II is correct
4. D.Both Statement I and Statement II are incorrect

For the reaction at $298\text{ K}$, $2\text{ A}+\text{B}\to \text{C}$, $\Delta H=400{\text{ kJ mol}}^{-1}$ and $\Delta S=0.2{\text{ kJ mol}}^{-1}{\text{ K}}^{-1}$. The reaction will become spontaneous above ________ $\text{K}$.

The correct order of first ionization enthalpy values of the following elements is : (A) O (B) N (C) Be (D) F (E) B Choose the correct answer from the options given below :

1. A.$\mathrm{A}<\mathrm{B}<\mathrm{D}<\mathrm{C}<\mathrm{E}$
2. B.$\mathrm{C}<\mathrm{E}<\mathrm{A}<\mathrm{B}<\mathrm{D}$
3. C.$\mathrm{E}<\mathrm{C}<\mathrm{A}<\mathrm{B}<\mathrm{D}$
4. D.$\mathrm{B}<\mathrm{D}<\mathrm{C}<\mathrm{E}<\mathrm{A}$

The enthalpy of formation of ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) from ethylene by addition of hydrogen where the bond-energies of $\mathrm{C}-\mathrm{H}$, $\mathrm{C}-\mathrm{C}$, $\mathrm{C}=\mathrm{C}$, $\mathrm{H}-\mathrm{H}$ are $414\mathrm{kJ}$, $347\mathrm{kJ}$, $615\mathrm{kJ}$ and $435\mathrm{kJ}$ respectively is $-$ ____ $\mathrm{kJ}$

The correct order of the first ionization enthalpy is

1. A.$\text{Ga}>\text{Al}>\text{B}$
2. B.$\text{Tl}>\text{Ga}>\text{Al}$
3. C.$\text{Al}>\text{Ga}>\text{Tl}$
4. D.$\text{B}>\text{Al}>\text{Ga}$

The transition metal having highest $3^{\text{rd}}$ ionisation enthalpy is :

1. A.$\mathrm{Mn}$
2. B.$\mathrm{Fe}$
3. C.$\mathrm{Cr}$
4. D.$V$

The correct sequence of electron gain enthalpy of the elements listed below is A. Ar B. Br C. F D. S Choose the most appropriate from the options given below:

1. A.$\mathrm{A}>\mathrm{D}>\mathrm{C}>\mathrm{B}$
2. B.$\mathrm{A}>\mathrm{D}>\mathrm{B}>\mathrm{C}$
3. C.$\mathrm{D}>\mathrm{C}>\mathrm{B}>\mathrm{A}$
4. D.$\mathrm{C}>\mathrm{B}>\mathrm{D}>\mathrm{A}$

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R : Assertion A : The first ionisation enthalpy decreases across a period. Reason R : The increasing nuclear charge outweighs the shielding across the period. In the light of the above statements, choose the most appropriate from the options given below :

1. A.A is false but R is true
2. B.Both A and R are true but R is NOT the correct explanation of A
3. C.Both A and R are true and R is the correct explanation of A
4. D.A is true but R is false

The element having the highest first ionization enthalpy is

1. A.$\mathrm{C}$
2. B.$\mathrm{Al}$
3. C.$\mathrm{Si}$
4. D.$\mathrm{N}$

Standard enthalpy of vapourisation for $\mathrm{CC}{\mathrm{l}}_4$ is $30.5{\text{ kJ mol}}^{-1}$. Heat required for vapourisation of $284\text{ g}$ of $\mathrm{CC}{\mathrm{l}}_4$ at constant temperature is _________ kJ. (Given molar mass in ${\mathrm{gmol}}^{-1}$; $\mathrm{C}=12,\mathrm{Cl}=35.5$)

For a certain thermochemical reaction $\text{M}\to \text{N}$ at $\text{T}=400\text{ K}$, $\Delta {\text{H}}^{\ominus }=77.2{\text{ kJ mol}}^{-1}$, $\Delta \text{S}=122{\text{ JK}}^{-1}$, log equilibrium constant ($\log K$) is _______ $\times 10^{-1}$.

What happens when methane undergoes combustion in systems A (Adiabatic system) and B (Diathermic container) respectively?

1. A.System A: Temperature falls; System B: Temperature rises
2. B.System A: Temperature rises; System B: Temperature remains same
3. C.System A: Temperature falls; System B: Temperature remains same
4. D.System A: Temperature remains same; System B: Temperature rises

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Isotopes of hydrogen have almost same chemical properties, but difference in their rates of reaction. Reason R : Isotopes of hydrogen have different enthalpy of bond dissociation. In the light of the above statements, choose the most appropriate answer from the options given below:

1. A.A is not correct but R is correct
2. B.Both A and R are correct but R is NOT the correct explanation of A
3. C.A is correct but R is not correct
4. D.Both A and R are correct and R is the correct explanation of A

Identify the correct order of standard enthalpy of formation of sodium halides :

1. A.$\mathrm{NaI}<\mathrm{NaBr}<\mathrm{NaCl}<\mathrm{NaF}$
2. B.$\mathrm{NaI}<\mathrm{NaBr}<\mathrm{NaF}<\mathrm{NaCl}$
3. C.$\mathrm{NaF}<\mathrm{NaCl}<\mathrm{NaBr}<\mathrm{NaI}$
4. D.$\mathrm{NaCl}<\mathrm{NaF}<\mathrm{NaBr}<\mathrm{NaI}$

One mole of an ideal gas at $350\text{ K}$ is in a $2.0\text{ L}$ vessel of thermally conducting walls, which are in contact with the surroundings. It undergoes isothermal reversible expansion from $2.0\text{ L}$ to $3.0\text{ L}$ against a constant pressure of $4\text{ atm}$. The change in entropy of the surroundings ( $\Delta \mathrm{S}$) is _________ ${\mathrm{JK}}^{-1}$ (Nearest integer) Given: $\mathrm{R}=8.314{\text{ J K}}^{-1}{\text{ mol}}^{-1}$.

For elements $\mathrm{B},\mathrm{C},\mathrm{N},\mathrm{Li},\mathrm{Be},\mathrm{O}$ and $\mathrm{F}$, the correct order of first ionization enthalpy is

1. A.$\mathrm{Li}<\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}$
2. B.$\mathrm{B}>\mathrm{Li}>\mathrm{Be}>\mathrm{C}>\mathrm{N}>\mathrm{O}>\mathrm{F}$
3. C.$\mathrm{Li}<\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{N}<\mathrm{O}<\mathrm{F}$
4. D.$\mathrm{Li}<\mathrm{B}<\mathrm{Be}<\mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}$

1. A.At $600^{\circ }\text{C}$, C can reduce FeO
2. B.At $600^{\circ }\text{C}$, C can reduce ZnO
3. C.At $600^{\circ }\text{C}$, CO can reduce ZnO
4. D.At $600^{\circ }\text{C}$, CO cannot reduce FeO

The number of endothermic process/es from the following is _________. A. ${\text{I}}_2(\text{g})\to 2\text{I}(\text{g})$ B. $\text{HCl}(\text{g})\to \text{H}(\text{g})+\text{Cl}(\text{g})$ C. ${\text{H}}_2\text{O}(\text{l})\to {\text{H}}_2\text{O}(\text{g})$ D. $\text{C}(\text{s})+{\text{O}}_2(\text{g})\to {\text{CO}}_2(\text{g})$ E. Dissolution of ammonium chloride in water

When a $60\text{ W}$ electric heater is immersed in a gas for $100\text{ s}$ in a constant volume container with adiabatic walls, the temperature of the gas rises by $5^{\circ }\text{C}$. The heat capacity of the given gas is ___________ $\mathrm{J}{\mathrm{K}}^{-1}$ (Nearest integer)

Ion having highest hydration enthalpy among the given alkaline earth metal ions is :

1. A.$\mathrm{S}{\mathrm{r}}^{2+}$
2. B.$\mathrm{C}{\mathrm{a}}^{2+}$
3. C.$\mathrm{B}{\mathrm{e}}^{2+}$
4. D.$\mathrm{B}{\mathrm{a}}^{2+}$

Consider the following data $$\begin{array}{rl}& \text{Heat of combustion of }{\mathrm{H}}_2(\mathrm{g})=-241.8{\text{ kJ mol}}^{-1}\\ & \text{Heat of combustion of }\mathrm{C}(\mathrm{s})=-393.5{\text{ kJ mol}}^{-1}\\ & \text{Heat of combustion of }{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{l})=-1234.7{\text{ kJ mol}}^{-1}\end{array}$$ The heat of formation of ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{l})$ is $(-)$ ___________ ${\text{kJ mol}}^{-1}$ (Nearest integer).

At $25^{\circ }\text{C}$, the enthalpy of the following processes are given : | Reaction | Enthalpy | | :--- | :--- | | ${\text{H}}_2(\text{g})+{\text{O}}_2(\text{g})\to 2\text{OH}(\text{g})$ | $\Delta {\text{H}}^{\circ }=78{\text{ kJ mol}}^{-1}$ | | ${\text{H}}_2(\text{g})+\frac{1}{2}{\text{O}}_2(\text{g})\to {\text{H}}_2\text{O}(\text{g})$ | $\Delta {\text{H}}^{\circ }=-242{\text{ kJ mol}}^{-1}$ | | ${\text{H}}_2(\text{g})\to 2\text{H}(\text{g})$ | $\Delta {\text{H}}^{\circ }=436{\text{ kJ mol}}^{-1}$ | | $\frac{1}{2}{\text{O}}_2(\text{g})\to \text{O}(\text{g})$ | $\Delta {\text{H}}^{\circ }=249{\text{ kJ mol}}^{-1}$ | What would be the value of X for the following reaction ? ________ (Nearest integer) $${\text{H}}_2\text{O}(\text{g})\to \text{H}(\text{g})+\text{OH}(\text{g})\Delta {\text{H}}^{\circ }={\text{X kJ mol}}^{-1}$$