A 32 g sample of CH 4 gas initially at 101 . 325 kPa and 300 K is heated to 550 K . C p . m . / JK - 1 mol - 1 = 12 . 552 + 8 . 368 × 10 - 2 T / K . Assuming CH 4 behaves ideally, compute w , q , ∆ U and ∆ H for (a) an isobaric reversible process and (b) an isochoric reversible process.

n = 2 V 1 = 2 × 0 . 0821 × 300 1 = 49 . 26 L V 1 T 1 = T 2 V 2 ⇒ 49 . 26 300 = V 2 550 ⇒ V 2 = 90 . 31 L (i) w = - P ∆ V = 1 90 . 31 - 49 . 26 = - 41 . 05 L - atm w = - 41 . 05 × 101 . 3 = - 4158 . 36 J = - 4 . 15 k q = ∆ H = ∫ nC P dT = 2 12 . 552 T 2 - T 1 + 8 . 368 × 10 - 3 2 T 2 2 - T 1 2 q = ∆ H = 2 12 . 552 250 + 8 . 368 × 10 - 2 2 212500 q = ∆ H = 24 . 04 kJ C v = C p - R = 4 . 238 + 8 . 368 × 10 - 2 T ∆ U = ∫ nC v dt = 19 . 9 kJ (iii) w = 0 q = ∆ U = 19 . 9 kJ ∆ H = ∫ nC P dT = 24 . 04 kJ Enthalpy is a state function.

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 ≡ C = 930 kJ / mol ; C = C = 615 kJ / mol ; C - C = 348 kJ / mol Give answer in interger number.

The resonance energy is defined as the difference between the electronic energy of a real (conjugated) molecule and a hypothetical Kekuléé structure with localized bonds. Given 6 C s + 3 H 2 g → C 6 H 6 l ∆ H = 49 C 6 H 6 l → C 6 H 6 g ∆ H = 45 So 6 C s + 3 H 2 g → C 6 H 6 g ∆ H = 94 . . . . i 2 C s + H 2 g → C 2 H 2 g ∆ H = 75 . . . . ii i - 3 × ii 3 C 2 H 2 g → C 6 H 6 g = 131 3 B C ≡ C + 2 B C - H - 3 B C - C + 3 B C = C + 6 B C - H - RE = - 131 3 B C ≡ C - B C - C - B C = C + RE = - 131 RE = - 131 + 99 = - 32

HARD

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IMPORTANT

Earn 100

Calculate work done in adiabatic compression of one mole of an ideal gas (monoatomic) from an initial pressure of $1 atm$ to final pressure of $2 atm$ . Initial temperature $= 300 K$

(a) If process is carried out reversibly

(b) If process is carried out irreversible against $2 atm$ external pressure.

Compute the final volume reached by gas in two cases.

Important Questions on Thermodynamics

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JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 5

10 g of neon initially at a pressure of 506.625 k Pa and temperature of 473 K expand adiabatically to a pressure of 202.65 k Pa. Calculate entropy change of the system for the following ways of carrying out this expansion.

(i) Expansion is carried out reversibly.
(ii) Expansion occurs against a constant external pressure of 202.65 k Pa.
(iii) Expansion is a free expansion.

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 8

Fixed amount of an ideal mono atomic gas contained in a sealed rigid vessel

(V = 24.6 litre)

1.0

bar is heated reversibly form

27 ° C

127 ° C .

Determine change in Gibb's energy (in Joule) if entropy of gas

S = 10 + 10^{- 2} T (J / K)

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IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 9

A $32 g$ sample of ${CH}_{4}$ gas initially at $101.325 kPa$ and $300 K$ is heated to $550 K$ . $C_{p . m .} / {JK}^{- 1} {mol}^{- 1} = 12.552 + 8.368 \times 10^{- 2} T / K$ . Assuming ${CH}_{4}$ behaves ideally, compute $w, q, ∆ U$ and $∆ H$ for

(a) an isobaric reversible process and

(b) an isochoric reversible process.

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JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 13

For the reaction cis-

2

-butene

\to

trans-

2

-butene and cis-

2

-butene

\to

1

-butene is

- 659.8 kcal / mol

. Determine the heat of combustion of trans-

2

-butene. Also calculate the bond energy of

C = C = 80

and

C - H = 98 kcal / mol

respectively.

∆ H_{v} (H_{2} O) = 11 kcal / mol

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JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 14

Using the data (all values are in

kJ / mol

25^{°} C

) given below:

(i) Enthalpy of polymerization of ethylene $= - 72$ .

(ii) Enthalpy of formation of benzene $(l) = 49$ .

(iii) Enthalpy of vaporization of benzene $(l) = 30$

(iv) Resonance energy of benzene $(l) = - 152$

(v) Heat of formation of gaseous atoms from the elements in their standard states $H = 218, C = 715$ .

Average bond energy of $C - H = 415$ . Calculate the B.E. of $C - C$ and $C = C$ . [ $A : 331$ and $590 kJ / mol$ ]

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JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 4 - Thermodynamics>EXERCISE-4>Q 15

Determine resonance energy of benzene

[C_{6} H_{6} (l)]

from the following information :

∆ H_{f}^{°}

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.

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JEE Main/Advance

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 ${CaC}_{2} (s)$ .

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JEE Main/Advance

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

Important Questions on Thermodynamics

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