Use the following enthalpies of combustion in the calculations that follow. Element/Compound Enthalpy of Combustion C s - 394 H 2 g - 286 CH 3 CO 2 H l - 876 C 4 H 6 g - 2542 C 2 H 6 g - 1561 C 2 H 4 g - 1393 (i) Calculate the enthalpy change for the reaction : 2 C s + 2 H 2 g + O 2 g → CH 3 CO 2 H l (ii) Calculate the enthalpy of formation of buta- 1 , 3 -diene C 4 H 6 . (iii) Calculate the enthalpy of formation of ethene C 2 H 4 . (iv) Calculate the enthalpy change for the conversion of ethene C 2 H 4 to ethane C 2 H 6 .

The change in enthalpy of a system when one mole of a substance is completely burnt in oxygen or air at a given temperature is known as the enthalpy of combustion. (I) ∆ H reac = 2 × ∆ H C C s + 2 × ∆ H C H 2 g - ∆ H C CH 3 COOH l = 2 × - 394 + 2 × - 286 - - 876 = - 788 - 572 + 876 = - 484 Joules ( II ) 2 C s + 5 H 2 g → C 4 H 6 g ∆ H rea c = 4 × ∆ H C C s + 3 × ∆ H C H 2 g - ∆ H C C 4 H 6 g = 4 × - 394 + 3 - 286 - - 2542 = 108 Joule III 2 C s + 2 H 2 g → C 2 H 4 g ∆ H reac = 2 × ∆ H C C s + 2 × ∆ H C H 2 g - ∆ H C C 2 H 4 g = 2 × - 394 + 2 - 286 - - 1393 = 33 Joule IV C 2 H 4 g + H 2 g → C 2 H 6 ( g ) ∆ H reac = ∆ H C C 2 H 4 + ∆ H C H 2 g - ∆ H C C 4 H 6 g = - 1393 + - 286 - 1561 = - 118 Joule

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IMPORTANT

Earn 100

Determine resonance energy of benzene $[C_{6} H_{6} (l)]$ from the following information : $∆ H_{f}^{°}$ of $C_{6} H_{6} (l) = + 49 kJ$ ;
$∆ H_{f}^{°}$ of $C_{2} H_{2} (g) = + 75 kJ ∆ H_{v}^{°}$ of $C_{6} H_{6} (l) = + 45 kJ$

$B . E . C \equiv C = 930 kJ / mol$ ; $C = C = 615 kJ / mol$ ; $C - C = 348 kJ / mol$

Give answer in interger number.

Important Questions on Thermodynamics

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 16

Consider the following thermodynamic data :

Enthalpy of formation of ${CaC}_{2} (s) = - 60 kJ / mol$ ;

Enthalpy of sublimation of $Ca (s) = 179 kJ / mol$ ;

Enthalpy of sublimation of $C (s) = 718 kJ / mol$ ;

First ionization energy of $Ca (g) = 590 kJ / mol$ ;

Second ionization energy of $Ca (g) = 1143 kJ / mol$ ;

Bond energy of $C_{2} (g) = 614 kJ / mol$ ;

First electron affinity of $C_{2} (g) = + 410 kJ / mol$ ;

Draw a clear Born-Haber cycle and determine lattice energy of ${CaC}_{2} (s)$ .

HARD

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 17

A swimmer breath

20

times in one minute when swimming and inhale

200 mL

of air in one breath. Inhalded air contain

20 %

O_{2}

by volume and exhaled air contain

10 %

O_{2}

by volume. If all oxygen is consumed in combustion of glucose in the body and

25 %

of energy obtained from combustion is available for muscular work. Determine the maximum distance this swimmer can swim in one hour if

100 kJ

Energy is required for

1.0 km

Swimming. Standard molar enthalpy of combustion of glucose is

- 2880 kJ / mol

and body temperature is

37^{°} C

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Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 20

Use the following enthalpies of combustion in the calculations that follow.

Element/Compound	Enthalpy of Combustion
$C (s)$	$- 394$
$H_{2} (g)$	$- 286$
${CH}_{3} {CO}_{2} H (l)$	$- 876$
$C_{4} H_{6} (g)$	$- 2542$
$C_{2} H_{6} (g)$	$- 1561$
$C_{2} H_{4} (g)$	$- 1393$

(i) Calculate the enthalpy change for the reaction :

$2 C (s) + 2 H_{2} (g) + O_{2} (g) \to {CH}_{3} {CO}_{2} H (l)$

(ii) Calculate the enthalpy of formation of buta- $1, 3$ -diene $C_{4} H_{6}$ .

(iii) Calculate the enthalpy of formation of ethene $C_{2} H_{4}$ .

(iv) Calculate the enthalpy change for the conversion of ethene $C_{2} H_{4}$ to ethane $C_{2} H_{6}$ .

HARD

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 25

Enthalpy for the reaction

{Ag}^{+} (aq) + {Br}^{-} (aq) \to AgBr (s)

- 84.54 kJ

. Magnitude of enthalpy of formation of

{Ag}^{+} (aq)

and

{Br}^{-} (aq)

are in the ratio

8 : 9

. Formation of

{Ag}^{+} (aq)

is an endothermic process whereas formation of

{Br}^{-}

is an exothermic process. Enthalpy of formation of

AgBr

- 99.54 kJ / mol

. Calculate the enthalpy of formation of

{Ag}^{+} (aq)

kJ / mol

EASY

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 26

25 ° C, {ΔH}_{f} (H_{2} O, l) = - 56700 J mol

and energy of ionization of

H_{2} O (l) = 19050 J mol

. What will be the reversible EMF at

25 ° C

of the cell,

Pt |H_{2} (g) (1 atm)| H^{+} | | {OH}^{-} |O_{2} (g) (1 atm)| Pt

, if at

26 ° C

the emf increase by

0.001158 V

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 27

Given are the following standard free energies of formation at $298 K$ .

$\begin{array}{l} CO (g) & {CO}_{2} (g) & H_{2} O (g) & H_{2} O (l) \\ \frac{Δ_{f} G °}{{kJmole}^{- 1}} & - 137.17 & - 394.36 & - 228.57 & - 237.13 \end{array}$

(a) Find $Δ_{r} G °$ and the standard equilibrium constant $K_{p}^{0}$ at $298 K$ for the reaction
$CO (g) + H_{2} O (g) ⇌ {CO}_{2} (g) + H_{2} (g)$

(b) If $CO, {CO}_{2}$ and $H_{2}$ are mixed so that the partial pressure of each is $101.325 kPa$ and the mixture is brought into contact with excess of liquid water, what will be the partial pressure of each gas when equilibrium is attained at $298 K$ . The volume available to the gases is constant.

Determine resonance energy of benzene C6H6l from the following information : ∆Hf° of C6H6l=+49 kJ ; ∆Hf° of C2H2g=+75 kJ ∆Hv° of C6H6l=+45 kJ B.E. C≡C=930 kJ/mol ; C=C=615 kJ/mol ; C-C=348 kJ/mol Give answer in interger number.

Important Questions on Thermodynamics

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