Calculate the enthalpy of reaction ∆ H , when ammonia is oxidized: 4 NH 3 ( g ) + 5 O 2 ( g ) → 6 H 2 O ( g ) + 4 NO ( g ) . Standard enthalpies of formation ∆ H ° at 25 ° C for NH 3 g , H 2 O g and NO g are - 46 . 2 , - 241 . 8 and + 90 . 4 kJ mole - 1 respectively.

Given, Enthalpy of formation of NH 3 = - 46 . 2 kJ mol - 1 . Enthalpy of formation of H 2 O = - 241 . 8 kJ mol - 1 . Enthalpy of formation of NO = + 90 . 4 kJ mol - 1 . ( A ) 4 NH 3 ( g ) + 5 O 2 ( g ) → 6 H 2 O ( l ) + 4 NO ( g ) , ΔH = ? Reaction Used, 1 2 N 2 + 3 2 H 2 → NH 3 , ΔH 1 = - 46 . 2 kJ mol - 1 ----- i . 1 2 O 2 + H 2 → H 2 O , ΔH 2 = - 241 . 8 kJ mol - 1 ----- ii . 1 2 N 2 + 1 2 O 2 → NO , ΔH 3 = + 90 . 4 kJ mol - 1 ----- iii . In order to get reaction ( A ) : 6 Eq ( ii ) + 4 Eq ( iii ) - 4 Eq ( i ) . 3 O 2 + 6 H 2 + 2 N 2 + 2 O 2 - 2 N 2 - 6 H 2 → 6 H 2 O + 4 NO - 4 NH 3 . 4 NH 3 + 5 O 2 → 6 H 2 O + 4 NO , ΔH = 6 ΔH 2 + 4 ΔH 3 - 4 ΔH 1 . ΔH = 6 ΔH 2 + 4 ΔH 3 - 4 ΔH 1 . ΔH = ( 6 × - 241 . 8 ) + ( 4 × 90 . 4 ) - ( 4 × – 46 . 2 ) . ΔH = - 1450 + 361 . 6 + 184 . 8 . ΔH = - 903 . 6 kJ mol - 1 .

Given that (i) C ( graphite ) + O 2 ( g ) → CO 2 ( g ) ; ΔH = – 393 . 7 kJ mol - 1 . (ii) C ( diamond ) → C ( graphite ) ; ΔH = – 2 . 1 kJ mol - 1 . Calculate ∆ H for burning of diamond to CO 2 .

Given, ( i ) C ( graphite ) + O 2 ( g ) → CO 2 ( g ) , ΔH 1 = - 393 . 7 kJ mol - 1 . ( ii ) C ( diamond ) → C ( graphite ) , ΔH 2 = - 2 . 1 kJ mol - 1 . C ( diamond ) + O 2 ( g ) → CO 2 ( g ) , ΔH = ? eq ( a ) = eq ( i ) + eq ( ii ) . ΔH = ΔH 1 + ΔH 2 . ΔH = - 393 . 7 - 2 . 1 = - 395 . 8 kJ mol - 1 . The enthalpy change for the burning of diamond to carbon dioxide is - 395 . 8 kJ mol - 1 .

Given that, (i) C ( graphite ) + O 2 ( g ) → CO 2 ( g ) ; ΔH = – 393 . 7 kJ mol - 1 . (ii) C ( diamond ) → C ( graphite ) ; ΔH = – 2 . 1 kJ mol - 1 . Calculate the quantity of graphite that must be burnt to evolve 5000 kJ of heat.

The graphite is an allotropic form of the carbon. It produces carbon dioxide along with heat energy during the combustion reaction. Given, C ( graphite ) + O 2 ( g ) → CO 2 ( g ) ; ΔH = – 393 . 7 kJ mol - 1 . 393 . 7 kJ of heat produced from one mole of graphite. i.e., 12 g of graphite. For the production of 1 kJ of heat, the required amount of graphite = 12 393 .7 g . Therefore, for the production of 5000 kJ of heat, the required amount of graphite = 12 393 .7 × 5000 g = 152 . 4 g .

EASY

11th CBSE

IMPORTANT

Earn 100

The enthalpies of formation of methane, carbon dioxide and water (liquid) are $- 74.8, - 393.5$ and $- 286.2 kJ$ respectively. Calculate the enthalpy of combustion of methane at ordinary temperature.

Important Questions on Thermodynamics

EASY

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 2

There are two crystalline forms of $PbO$ ; one is yellow and the other is red. The standard enthalpies of formation of these two forms are $- 217.3$ and $- 219.0 kJ {mol}^{- 1}$ respectively. Calculate the enthalpy change for the solid-solid phase transition.

$PbO (yellow) \to PbO (red)$ .

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 3

The enthalpy of solution of anhydrous copper sulphate

({CuSO}_{4})

and hydrated copper sulphate

({CuSO}_{4} . 5 H_{2} O)

are

- 66.5

and

+ 11.7 kJ {mol}^{- 1}

respectively. Calculate the enthalpy of hydration of anhydrous copper sulphate to pentahydrate.

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 1

The enthalpies of formation of carbon monoxide and steam are

- 110.5

and

- 243.0 kJ {mol}^{- 1}

respectively. Calculate the enthalpy of the reaction when steam is passed over coke, i.e., for the reaction

C + H_{2} O \to CO + H_{2}

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 2

Chloroform is prepared from methane according to the reaction:

{CH}_{4} (g) + 3 {Cl}_{2} (g) \to {CHCl}_{3} (l) + 3 HCl (g)

Calculate

∆ H

for the reaction given that enthalpies of formation of

HCI (g)

{CH}_{4} (g)

and

{CHCl}_{3} (l)

are

- 92.0, - 74.9

and

- 134.3 kJ {mol}^{- 1}

respectively.

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 3

Calculate the enthalpy of reaction $(∆ H)$ , when ammonia is oxidized: $4 {NH}_{3} (g) + 5 O_{2} (g) \to 6 H_{2} O (g) + 4 NO (g)$ .

Standard enthalpies of formation $(∆ H °)$ at $25 ° C$ for ${NH}_{3} (g), H_{2} O (g)$ and $NO (g)$ are $- 46.2, - 241.8$ and $+ 90.4 kJ {mole}^{- 1}$ respectively.

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 4

The standard enthalpy of formation of ${Fe}_{2} O_{3} (s)$ is $- 824.2 kJ {mol}^{- 1}$ . Calculate the enthalpy change for the reaction:

$4 Fe (s) + 3 O_{2} (g) \to 2 {Fe}_{2} O_{3} (s)$ .

EASY

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 1

Given that (i) $C (graphite) + O_{2} (g) \to {CO}_{2} (g); ΔH = - 393.7 kJ {mol}^{- 1}$ .

(ii) $C (diamond) \to C (graphite); ΔH = - 2.1 kJ {mol}^{- 1}$ .

Calculate $∆ H$ for burning of diamond to ${CO}_{2}$ .

HARD

11th CBSE

IMPORTANT

Pradeep's Chemistry Vol 1>Chapter 7 - Thermodynamics>PROBLEMS FOR PRACTICE>Q 1

Given that,

(i) $C (graphite) + O_{2} (g) \to {CO}_{2} (g); ΔH = - 393.7 kJ {mol}^{- 1}$ .
(ii) $C (diamond) \to C (graphite); ΔH = - 2.1 kJ {mol}^{- 1}$ .

Calculate the quantity of graphite that must be burnt to evolve $5000 kJ$ of heat.

The enthalpies of formation of methane, carbon dioxide and water (liquid) are -74.8, -393.5 and -286.2 kJ respectively. Calculate the enthalpy of combustion of methane at ordinary temperature.

Important Questions on Thermodynamics

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The enthalpies of formation of methane, carbon dioxide and water (liquid) are $- 74.8, - 393.5$ and $- 286.2 kJ$ respectively. Calculate the enthalpy of combustion of methane at ordinary temperature.