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According to Hess’s law, the heat of reaction depends upon

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Important Questions on Chemical Thermodynamics

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Write Hess's law of constant heat summation.

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Given:

(i)

C (graphite) + O_{2} (g) \to {CO}_{2} (g);

{ΔrH}^{Θ} = x kJ {mol}^{- 1}

(ii)

C (graphite) + \frac{1}{2} O_{2} (g) \to CO (g);

{ΔrH}^{Θ} = y kJ {mol}^{- 1}

(iii) CO (g) + \frac{1}{2} O_{2} (g) \to {CO}_{2} (g);

{ΔrH}^{Θ} = z kJ {mol}^{- 1}

Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

State and explain Hess’s law of constant heat summation.

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Given

(A) $2 CO (g) + O_{2} (g) \to 2 {CO}_{2} (g) {ΔH}_{1}^{o} = - x kJ {mol}^{- 1}$

(B) $C (graphite) + O_{2} (g) \to {CO}_{2} (g) {ΔH}_{2}^{o} = - y kJ {mol}^{- 1}$

The $∆ H^{o}$ for the reaction $C (graphite) + \frac{1}{2} O_{2} (g) \to CO (g)$ is

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Hess law states that,

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The enthalpy change for the conversion of

\frac{1}{2} {Cl}_{2}

(g) to

{Cl}^{-} (aq)

(-)

{kJmol}^{- 1}

(Nearest integer)
Given :

Δ_{dis} H_{{Cl}_{2 (g)}}^{0} = 240 {kJmol}^{- 1}

Δ_{eg} H_{Cl (g)}^{o} = - 350 {kJmol}^{- 1}

Δ_{hyd} H_{{Cl}_{(g)}^{-}}^{o} = - 380 {kJmol}^{- 1}

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

State and explain Hess’s law of constant heat summation.

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The correct thermodynamic conditions for the spontaneous reaction at all temperatures is:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The ionization enthalpy of

{Na}^{+}

formation from

{Na}_{(g)}

495.8 kJ {mol}^{- 1},

while the electron gain enthalpy of

Br

- 325.0 kJ {mol}^{- 1}

. Given the lattice enthalpy of

NaBr

- 728.4 kJ {mol}^{- 1}

. The energy for the formation of

NaBr

ionic solid is

(-)_____10^{- 1} kJ {mol}^{- 1}

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The Born-Haber cycle for $KCl$ is evaluated with the following data:
$Δ_{f} H^{Θ} for KCl = - 436.7 {kJmol}^{- 1}; Δ_{sub} H^{Θ} for K = 89.2 {kJmol}^{- 1};$

$Δ_{ionization} H^{Θ} for K = 419.0 kJ {mol}^{- 1}; Δ_{electron gain} H^{Θ} for {Cl}_{(g)} = - 348.6 {kJmol}^{- 1}$

$Δ_{bond} H^{Θ} for {Cl}_{2} = 243.0 {kJmol}^{- 1}$
The magnitude of lattice enthalpy of $KCl$ in ${kJmol}^{- 1}$ is (Nearest integer)

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Consider the following data

Heat of combustion of $H_{2} (g) = - 241.8 kJ {mol}^{- 1}$

Heat of combustion of $C (s) = - 393.5 kJ {mol}^{- 1}$

Heat of combustion of $C_{2} H_{5} OH (l)$ $= - 1234.7 kJ {mol}^{- 1}$

The heat of formation of $C_{2} H_{5} OH (l)$ is $(-)$ _____ $kJ {mol}^{- 1}$ (Nearest integer).

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

C (s) + O_{2} (g) \to C O_{2} (g), Δ H = - X,

C O (g) + \frac{1}{2} O_{2} (g) \to C O_{2} (g), Δ H = - Y,

Calculate

Δ_{f} H

for

C O_{(g)}

formation

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Solid fuel used in rocket is a mixture of ${Fe}_{2} O_{3}$ and $Al$ (in ratio $1 : 2$ ). The heat evolved $(kJ)$ per gram of the mixture is _____ (Nearest integer)

Given ${ΔH}_{f}^{0} ({Al}_{2} O_{3}) = - 1700 kJ {mol}^{- 1}$

${ΔH}_{f}^{0} ({Fe}_{2} O_{3}) = - 840 kJ {mol}^{- 1}$

Molar mass of $Fe, AI$ and $O$ are $56, 27$ and $16 g {mol}^{- 1}$ respectively

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

At $25 ° C$ , the enthalpy of the following processes are given:

$H_{2} (g) + O_{2} (g) \to 2 OH (g) Δ H^{o} = 78 kJ {mol}^{- 1}$

$H_{2} (g) + 1 / 2 O_{2} (g) \to H_{2} O (g) Δ H^{0} = - 242 kJ {mol}^{- 1}$

$H_{2} (g) \to 2 H (g) Δ H^{o} = 436 kJ {mol}^{- 1}$

$1 / 2 O_{2} (g) \to O (g) Δ H^{0} = 249 kJ {mol}^{- 1}$

What would be the value of X for the following reaction? (Nearest integer)

$H_{2} O (g) \to H (g) + OH (g) ∆ H^{o} = X {kJmol}^{- 1}$

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

One mole of an ideal gas at

300 K

in thermal contact with its surroundings expands isothermally from

1.0 L

2.0 L

against a constant pressure of

3.0 atm

. In this process, the change in entropy of the surroundings

(∆ S_{s u r r})

J K^{- 1}

is:

(1 L atm = 101.3 J)

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The entropy change associated with the conversion of

1 k g

of ice at

273 K

to water vapours at

383 K

is:

(Specific heat of water liquid and water vapour are

4.2 k J K^{-}

and

2.0 k J K^{- 1} k g^{- 1}

; heat of liquid fusion and vaporization of water are

334 k J k g^{- 1}

and

2491 k J k g^{- 1}

, respectively). (

l o g

273 = 2.436, \log 373 = 2.572, \log 383 = 2.583

)

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

A process has

Δ H = 200 J m o l^{- 1}

and

Δ S = 40 J K^{- 1} m o l^{- 1} .

Out of the values given below choose the minimum temperature above which the process will be spontaneous:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The enthalpy of combustion of propane, graphite and dihydrogen at

298 K

are:

- 2220.0 kJ {mol}^{- 1}

- 393.5 kJ {mol}^{- 1}

and

- 285.8 kJ {mol}^{- 1}

, respectively. The magnitude of enthalpy of formation of propane

(C_{3} H_{8})

is _____

{kJmol}^{- 1}

. (Nearest integer)

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Given that, the molar combustion enthalpy of benzene, cyclohexane and hydrogen are

x, y

and

z

, respectively, the molar enthalpy of hydrogenation of benzene to cyclohexane is

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Given

NO (g) + O_{3} (g) \to {NO}_{2} (g) + O_{2} (g) ∆ H = - 198 .9 kJ / mol

O_{3} (g) \to 3 / 2 O_{2} (g) ∆ H = - 142 .3 kJ / mol

O_{2} (g) \to 2 O (g) ∆ H = + 495 .0 kJ / mol

The enthalpy change

(∆ H)

for the following reaction is

N O (g) + O (g) \to N O_{2} (g)

According to Hess’s law, the heat of reaction depends upon

Important Questions on Chemical Thermodynamics

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