Use the following data to calculate the enthalpy of formation of As 2 O 3 . i As 2 O 3 s + 3 H 2 O aq . → 2 H 3 AsO 3 aq . ; ∆ H = + 7550 cal ii As s + 3 2 Cl 2 g → AsCl 3 l ; ∆ H = - 71390 cal iii AsCl 3 l + 3 H 2 O aq . → H 3 AsO 3 aq . + 3 HCl aq . ; ∆ H = - 17580 cal iv HCl g + aq . → HCl aq . ; ∆ H = - 17315 cal v 1 2 H 2 g + 1 2 Cl 2 g → HCl g ; ∆ H = - 22000 cal vi H 2 g + 1 2 O 2 g → H 2 O l ; ∆ H = - 68360 cal

i As 2 O 3 s + 3 H 2 O aq . → 2 H 3 AsO 3 aq . ; ∆ H = + 7550 cal ii As s + 3 2 Cl 2 g → AsCl 3 l ; ∆ H = - 71390 cal iii AsCl 3 l + 3 H 2 O aq . → H 3 AsO 3 aq . + 3 HCl aq . ; ∆ H = - 17580 cal iv HCl g + aq . → HCl aq . ; ∆ H = - 17315 cal v 1 2 H 2 g + 1 2 Cl 2 g → HCl g ; ∆ H = - 22000 cal vi H 2 g + 1 2 O 2 g → H 2 O l ; ∆ H = - 68360 cal The required reaction is vii 2 As s + 3 2 O 2 g → As 2 O 3 s ; ∆ H f ( As 2 O 3 ) = ? Above reaction can be obtained by the following steps: a) multiply equation (ii) and (iii) with 2 b) multiply equation (vi) with 3 c) multiply equation (iv) and (v) with 6 d) multiply equation (iv) with 6 e) multiply equation (v) with 6 Now Add equations (ii), (iii) and (vi) after performing the above given operations and subtract equations (i), (iv) and (v) by after performing the above given operations. All the operations done on reactions will also be done one their enthalpies as: Enthalpy is an extensive property. Thus, on multiplying the reaction by a number, it's enthalpy is also multiplied by the same number. According to Hess's law, the enthalpy of a complex reaction is equal to the summation of enthalpies of the individual steps in the reaction. ∆ H f As 2 O 3 = ( 2 ∆ H 2 ) + ( 2 ∆ H 3 ) + ( 3 ∆ H 6 ) - ( ∆ H 1 ) - ( 6 ∆ H 4 ) - ( 6 ∆ H 5 ) ∆ H f As 2 O 3 = ( 2 × - 71390 ) + ( 2 × - 17580 ) + ( 3 × - 68360 ) - ( + 7550 ) - ( 6 × - 17315 ) - ( 6 × - 22000 ) ∆ H f As 2 O 3 = - 154 . 68 kcal .

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IMPORTANT

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The heat evolved during the combustion of $46 g$ ethanol in a bomb calorimeter (constant pressure) was determined to be $670.48 kcal {mol}^{- 1}$ at $25 ° C$ . The value of $ΔU$ of the reaction at the same temperature is

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Important Questions on Thermodynamics

MEDIUM

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.2>Q 9

Which of the following is/are correct

MEDIUM

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.2>Q 10

For which of the following reaction(s) will

ΔH

and

ΔE

be equal?

MEDIUM

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.2>Q 13

For the reaction,

$N_{2} (g) + 3 H_{2} (g) \to 2 {NH}_{3} (g)$

Heat of reaction at constant volume exceeds the heat of reaction at constant pressure by the value of $xRT$ . The value of $x$ is ____.

HARD

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.3>Q 1

Standard heat of combustion of

C_{2} H_{2} (g)

and

C_{2} H_{4} (g)

are

- 310 .6 kcal

and

- 337 .2 kcal

per mole respectively. The heat of formation of water is

- 68 .3 kcal {mol}^{- 1}

. Calculate the heat of hydrogenation of

C_{2} H_{2} (g)

C_{2} H_{4} (g)

HARD

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.3>Q 2

Calculate the enthalpy of polymerisation of acetylene to benzene from the following data:

$C_{6} H_{6} (l) + 15 / 2 O_{2} (g) \to 6 {CO}_{2} (g) + 3 H_{2} O (g)$ ; $ΔH = - 3344.48 kJ$

$C_{2} H_{2} (g) + 5 / 2 O_{2} (g) \overset{}{\to} 2 {CO}_{2} (g) + H_{2} O (g); ∆ H = - 1297.25 kJ$

HARD

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.3>Q 3

Use the following data to calculate the enthalpy of formation of ${As}_{2} O_{3}$ .

$i) {As}_{2} O_{3} (s) + 3 H_{2} O (aq .) \to 2 H_{3} {AsO}_{3} (aq .); ∆ H = + 7550 cal ii) As (s) + \frac{3}{2} {Cl}_{2} (g) \to {AsCl}_{3} (l); ∆ H = - 71390 cal iii) {AsCl}_{3} (l) + 3 H_{2} O (aq .) \to H_{3} {AsO}_{3} (aq .) + 3 HCl (aq .); ∆ H = - 17580 cal iv) HCl (g) + aq . \to HCl (aq .); ∆ H = - 17315 cal v) \frac{1}{2} H_{2} (g) + \frac{1}{2} {Cl}_{2} (g) \to HCl (g); ∆ H = - 22000 cal vi) H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); ∆ H = - 68360 cal$

HARD

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.3>Q 4

A person takes

20 breaths / \min

. The amount of air inhaled per breath is

500

mL

. The inhaled air contains

5 %

by volume of oxygen. If enthalpy of combustion of sugar is

- 3690 J / mol

and all the oxygen taken in is used for combustion of sugar

(C_{12} H_{22} O_{11})

, find out the amount of heat energy liberated (in

kJ

) per day by combustion of sugar. (Air is inhaled at

1

atm

and

27 ° C

)

HARD

JEE Main

IMPORTANT

Chapterwise/Topicwise Daily Practice Problems (DPP) Physical Chemistry Part 1 JEE Main & Advanced>Chapter 5 - Thermodynamics>DPP 5.3>Q 5

An intimate mixture of ferric oxide, ${Fe}_{2} O_{3}$ and aluminium, is used in solid fuel of rockets. Determine the fuel value in $J / g$ and in $J / {cm}^{3}$ of the mixture. Given:

$Δ_{f} H ({Al}_{2} O_{3}, s) = - 1669 kJ / mol$

$Δ_{f} H ({Fe}_{2} O_{3}, s) = - 833 kJ / mol$

Density of ${Fe}_{2} O_{3} = 5.2 gm / {cm}^{3}, Molar mass of Fe = 56 g {mol}^{- 1}, O = 16 g {mol}^{- 1}$

Density of $Al = 2.7 gm / {cm}^{3}, Molar mass of Al = 27 g {mol}^{- 1}$

The heat evolved during the combustion of 46 g ethanol in a bomb calorimeter (constant pressure) was determined to be 670.48 kcal mol-1at 25°C. The value of ΔU of the reaction at the same temperature is

Important Questions on Thermodynamics

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The heat evolved during the combustion of $46 g$ ethanol in a bomb calorimeter (constant pressure) was determined to be $670.48 kcal {mol}^{- 1}$ at $25 ° C$ . The value of $ΔU$ of the reaction at the same temperature is