Enthalpy and Hess's Law

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JEE Advanced 2019

Choose the reaction(s) from the following options, for which the standard enthalpy of reaction is equal to the standard enthalpy of formation.

\frac{3}{2} O_{2} (g) \to O_{3} (g)

(B)

\frac{1}{8} S_{8} (s) + O_{2} (g) \to SO_{2} (g)

(C)

2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l)

(D)

2 C (g) + 3 H_{2} (g) \to C_{2} H_{6} (g)

JEE Main 2021

LEVELJEE Main

For the reaction, $C_{2} H_{6} ⟶ C_{2} H_{4} + H_{2}$ the reaction enthalpy $Δ_{r} H = \dots\dots\dots kJ mol^{- 1}$ (Round off to the nearest integer). [Given : Bond enthalpies in $kJ mol^{- 1}$ : $C - C = 347, C = C = 611; C - H = 414; H - H = 436$ ]

JEE Main 2020

LEVELJEE Main

The standard heat of formation ( $Δ_{f} H_{298}^{\circ}$ ) 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 ………

JEE Main 2020

LEVELJEE Main

If enthalpy of atomisation for $Br_{2} (l)$ is $x kJ/mol$ and bond enthalpy for $Br_{2}$ is $y kJ/mol$ , the relation between them

(A)

x < y

(B)

does not exist

(C)

x > y

(D)

x = y

LEVELJEE Main

On the basis of the following thermochemical data $[Δ_{f} G^{\circ} H^{+} (a q) = 0]$ $H_{2} O (l) ⟶ H^{+} (a q) + O H^{-} (a q); Δ H = 57.32 kJ$ $H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l); Δ H = - 286.20 kJ$ The value of enthalpy of formation of $O H^{-}$ ion at $2 5^{\circ} C$ is

(A)

- 22.88 kJ

(B)

- 228.88 kJ

(C)

+ 228.88 kJ

(D)

- 343.52 kJ

JEE Main 2021

LEVELJEE Advanced

At $298.2 K$ the relationship between enthalpy of bond dissociation (in $kJ mol^{- 1}$ ) for hydrogen ( $E_{H}$ ) and its isotope, deuterium ( $E_{D}$ ), is best described by

(A)

E_{H} = \frac{1}{2} E_{D}

(B)

E_{H} = E_{D}

(C)

E_{H} ≃ E_{D} - 7.5

(D)

E_{H} = 2 E_{D}

JEE Main 2021

LEVELJEE Main

The ionisation enthalpy of $Na^{+}$ formation from $Na (g)$ is $495.8 kJ mol^{- 1}$ , while the electron gain enthalpy of Br is $- 325.0 kJ mol^{- 1}$ . Given, the lattice enthalpy of NaBr is $- 728.4 kJ mol^{- 1}$ . The energy for the formation of NaBr ionic solid is $(-) \dots\dots \times 1 0^{- 1} kJ mol^{- 1}$ .

JEE Main 2019

LEVELJEE Main

Given : (i) $C(graphite) + O_{2} (g) \to CO_{2} (g)$ ; $Δ_{r} H^{\circ} = x kJ mol^{- 1}$ (ii) $C(graphite) + \frac{1}{2} O_{2} (g) \to CO_{2} (g)$ ; $Δ_{r} H^{\circ} = y kJ mol^{- 1}$ (iii) $CO (g) + \frac{1}{2} O_{2} (g) \to CO_{2} (g)$ ; $Δ_{r} H^{\circ} = z kJ mol^{- 1}$ Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?

(A)

y = 2 z - x

(B)

x = y - z

(C)

z = x + y

(D)

x = y + z

JEE Main 2019

LEVELJEE Main

Enthalpy of sublimation of iodine is $24 cal g^{- 1}$ at $20 0^{\circ} C$ . If specific heat of $I_{2} (s)$ and $I_{2} (vap.)$ are $0.055$ and $0.031 cal g^{- 1} K^{- 1}$ respectively, then enthalpy of sublimation of iodine at $25 0^{\circ} C$ in $cal g^{- 1}$ is

The heats of combustion of carbon and carbon monoxide are $- 393.5$ and $- 283.5 kJ mol^{- 1}$ , respectively. The heat of formation (in kJ) of carbon monoxide per mole is

(A)

676.5

(B)

- 676.5

(C)

- 110.5

(D)

110.5

LEVELJEE Main

Oxidising power of chlorine in aqueous solution can be determined by the parameters indicated below $\frac{1}{2} C l_{2} (g) \frac{1}{2} Δ_{d i ss} H^{⊖} C l (g) Δ_{E A} H^{⊖} C l^{-} (g) Δ_{h y d} H^{⊖} C l^{-} (a q)$ The energy involved in the conversion of $\frac{1}{2} C l_{2} (g)$ to $C l^{-} (a q)$ (using the data, $Δ_{d i ss} H_{C l_{2}}^{⊖} = 240 kJ mol^{- 1}$ , $Δ_{E A} H_{C l}^{⊖} = - 349 kJ mol^{- 1}$ , $Δ_{h y d} H_{C l^{-}}^{⊖} = - 381 kJ mol^{- 1}$ ) will be

(A)

+ 152 kJ mol^{- 1}

(B)

- 610 kJ mol^{- 1}

(C)

- 850 kJ mol^{- 1}

(D)

+ 120 kJ mol^{- 1}

JEE Main 2021

LEVELJEE Main

The standard enthalpies of formation of $Al_{2} O_{3}$ and $CaO$ are $- 1675 kJ mol^{- 1}$ and $- 635 kJ mol^{- 1}$ respectively. For the reaction, $3 CaO + 2 Al ⟶ 3 Ca + Al_{2} O_{3}$ the standard reaction enthalpy $Δ_{r} H^{\circ}$ ......... kJ. (Round off to the nearest integer).

LEVELJEE Main

The standard enthalpy of formation of $NH_{3}$ is $- 46.0 kJ mol^{- 1}$ . If the enthalpy of formation of $H_{2}$ from its atoms is $- 436 kJ mol^{- 1}$ and that of $N_{2}$ is $- 712 kJ mol^{- 1}$ , the average bond enthalpy of N—H bond in $NH_{3}$ is

(A)

- 964 kJ mol^{- 1}

(B)

+ 352 kJ mol^{- 1}

(C)

+ 1056 kJ mol^{- 1}

(D)

- 1102 kJ mol^{- 1}

LEVELBoard

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 involved substances

JEE Main 2021

LEVELJEE Main

200 mL of 0.2 M HCl is mixed with 300 mL of 0.1 M NaOH. The molar heat of neutralisation of this reaction is $- 57.1 kJ$ . The increase in temperature in $^{\circ} C$ of the system on mixing is $x \times 1 0^{- 2}$ . The value of $x$ is ......... (Nearest integer) [Given, specific heat of water = $4.18 J g^{- 1} K^{- 1}$ Density of water = $1.00 g cm^{- 3}$ ] (Assume no volume change on mixing)

JEE Main 2020

LEVELJEE Main

The heat of combustion of ethanol into carbon dioxides and water is $- 327 kcal$ at constant pressure. The heat evolved (in cal) at constant volume and $2 7^{\circ} C$ (if all gases behave ideally) is ( $R = 2 cal mol^{- 1} K^{- 1}$ ) .........

JEE Main 2006

LEVELJEE Advanced

The enthalpy changes for the following processes are listed below $Cl_{2} (g) = 2 Cl (g), 242.3 kJ mol^{- 1}$ $I_{2} (g) = 2 I (g), 151.0 kJ mol^{- 1}$ $ICl (g) = I (g) + Cl (g), 211.3 kJ mol^{- 1}$ $I_{2} (s) = I_{2} (g), 62.76 kJ mol^{- 1}$ Given that the standard states for iodine and chlorine are $I_{2} (s)$ and $Cl_{2} (g)$ , the standard enthalpy of formation of ICl is

(A)

- 14.6 kJ mol^{- 1}

(B)

- 16.8 kJ mol^{- 1}

(C)

+ 16.8 kJ mol^{- 1}

(D)

+ 244.8 kJ mol^{- 1}

JEE Main 2017

LEVELJEE Main

Given, $C_{(graphite)} + O_{2} (g) ⟶ C O_{2} (g)$ ; $Δ_{r} H^{\circ} = - 393.5 kJ mol^{- 1}$ $H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l)$ ; $Δ_{r} H^{\circ} = - 285.8 kJ mol^{- 1}$ $C O_{2} (g) + 2 H_{2} O (l) ⟶ C H_{4} (g) + 2 O_{2} (g)$ ; $Δ_{r} H^{\circ} = + 890.3 kJ mol^{- 1}$ Based on the above thermochemical equations, the value of $Δ_{r} H^{\circ}$ at 298 K for the reaction, $C_{(graphite)} + 2 H_{2} (g) ⟶ C H_{4} (g)$ will be

(A)

+ 78.8 kJ mol^{- 1}

(B)

+ 144.0 kJ mol^{- 1}

(C)

- 74.8 kJ mol^{- 1}

(D)

- 144.0 kJ mol^{- 1}

LEVELJEE Main

If at 298 K, the bond energies of C—H, C—C, C=C and H—H bonds are respectively 414, 347, 615 and 435 kJ mol $^{- 1}$ , the value of enthalpy change for the reaction, $H_{2} C = CH_{2} (g) + H_{2} (g) ⟶ H_{3} C — CH_{3} (g)$ at 298 K will be

If the bond dissociation energies of $X Y$ , $X_{2}$ and $Y_{2}$ (all diatomic molecules) are in the ratio of $1 : 1 : 0.5$ and $Δ H_{f}$ for the formation of $X Y$ is $- 200 kJ mol^{- 1}$ . The bond dissociation energy of $X_{2}$ will be

(A)

400 kJ mol^{- 1}

(B)

300 kJ mol^{- 1}

(C)

200 kJ mol^{- 1}

Lattice enthalpy and enthalpy of solution of NaCl are $788 kJ mol^{- 1}$ and $4 kJ mol^{- 1}$ , respectively. The hydration enthalpy of NaCl is

(A)

- 780 kJ mol^{- 1}

(B)

780 kJ mol^{- 1}

(C)

- 784 kJ mol^{- 1}

(D)

784 kJ mol^{- 1}

JEE Main 2021

LEVELBoard

At $298 K$ , the enthalpy of fusion of a solid (X) is $2.8 kJ mol^{- 1}$ and the enthalpy of vaporisation of the liquid (X) is $98.2 kJ mol^{- 1}$ . The enthalpy of sublimation of the substance (X) in $kJ mol^{- 1}$ is ...... (Nearest integer)

LEVELJEE Main

The standard enthalpy of formation ( $Δ H_{f}^{\circ}$ ) at $298 K$ for methane, $CH_{4} (g)$ is $- 74.8 kJ mol^{- 1}$ . The addition information required to determine the average energy for C—H bond formation would be

(A)

the dissociation energy of

H_{2}

and enthalpy of sublimation of carbon

(B)

latent heat of vaporisation of methane

(C)

the first four ionisation energies of carbon and electron gain enthalpy of hydrogen

(D)

the dissociation energy of hydrogen molecule,

H_{2}

JEE Main 2021

LEVELBoard

If the standard molar enthalpy change for combustion of graphite powder is $- 2.48 \times 1 0^{2} kJ mol^{- 1}$ , the amount of heat generated on combustion of $1 g$ of graphite powder is ...... kJ. (Nearest integer)

JEE Main 2021

LEVELJEE Advanced

When 400 mL of 0.2 M $H_{2} SO_{4}$ solution is mixed with 600 mL of 0.1 M NaOH solution, the increase in temperature of the final solution is ............... $\times 1 0^{- 2}$ K. (Round off to the nearest integer). [Use : $H^{+} (a q) + OH^{-} (a q) ⟶ H_{2} O$ ; $Δ_{y} H = - 57.1 kJ mol^{- 1}$ ] Specific heat of $H_{2} O = 4.18 J K^{- 1} g^{- 1}$ , density of $H_{2} O = 1.0 g cm^{- 3}$ . Assume no change in volume of solution on mixing.

Choose the reaction(s) from the following options, for which the standard enthalpy of reaction is equal to the standard enthalpy of formation.

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } If enthalpy of atomisation for Br2​(l) is x kJ/mol and bond enthalpy for Br2​ is y kJ/mol, the relation between them

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } At 298.2 K the relationship between enthalpy of bond dissociation (in kJ mol−1) for hydrogen (EH​) and its isotope, deuterium (ED​), is best described by

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } The heats of combustion of carbon and carbon monoxide are −393.5 and −283.5 kJ mol−1, respectively. The heat of formation (in kJ) of carbon monoxide per mole is

The enthalpy change for a reaction does not depend upon the

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Lattice enthalpy and enthalpy of solution of NaCl are 788 kJ mol−1 and 4 kJ mol−1, respectively. The hydration enthalpy of NaCl is

If enthalpy of atomisation for $Br_{2} (l)$ is $x kJ/mol$ and bond enthalpy for $Br_{2}$ is $y kJ/mol$ , the relation between them

At $298.2 K$ the relationship between enthalpy of bond dissociation (in $kJ mol^{- 1}$ ) for hydrogen ( $E_{H}$ ) and its isotope, deuterium ( $E_{D}$ ), is best described by

The heats of combustion of carbon and carbon monoxide are $- 393.5$ and $- 283.5 kJ mol^{- 1}$ , respectively. The heat of formation (in kJ) of carbon monoxide per mole is

Lattice enthalpy and enthalpy of solution of NaCl are $788 kJ mol^{- 1}$ and $4 kJ mol^{- 1}$ , respectively. The hydration enthalpy of NaCl is