1
MCQ (Single Correct Answer)

AIPMT 2004

Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is
A
$$\Delta {S_{system}} + \Delta {S_{surroundings}} > 0$$
B
$$\Delta {S_{system}} - \Delta {S_{surroundings}} > 0$$
C
$$\Delta {S_{system}} > 0\,\,\,$$only
D
$$\Delta {S_{surroundings}} > 0$$ only

Explanation

For the reaction to be spontaneous, the total entropy of system and universe increases i.e.,

$$\Delta {S_{system}} + \Delta {S_{surroundings}} > 0$$
2
MCQ (Single Correct Answer)

AIPMT 2004

Standard enthalpy and standard entropy changes for the oxidation of ammonia at 298 K are $$-$$ 382.64 kJ mol$$-$$1 and $$-$$ 145.6 kJ mol$$-$$1, respectively. Standard Gibb's energy change for the same reaction at 298 K is
A
$$-$$ 221.1 kJ mol$$-$$1
B
$$-$$339.3 kJ mol$$-$$1
C
$$-$$ 439.3 kJ mol$$-$$1
D
$$-$$ 523.2 kJ mol$$-$$1

Explanation

$$\Delta $$G = $$\Delta $$H – T$$\Delta $$S

$$\Delta $$G = –382.64 × 103 J mol–1 – (298K) (–145.6 JK–1 mol–1)

= –382640 + 43388.8

= – 339251.2 J mol–1 = – 339.3 kJ mol–1
3
MCQ (Single Correct Answer)

AIPMT 2004

If the bond energies of H $$-$$ H, Br $$-$$ Br, and H $$-$$ Br are 433, 192 and 364 kJ mol$$-$$1 respectively, the $$\Delta $$Ho for the reaction

H2(g) + Br2(g) $$ \to $$ 2HBr(g) is
A
$$-$$ 261 kJ
B
+103 kJ
C
+261 kJ
D
$$-$$103 kJ

Explanation

H2(g) + Br2(g) $$ \to $$ 2HBr(g),   $$\Delta $$Hof = ?

$$\Delta $$Hof = $$\Sigma $$(B.E.)reactants – $$\Sigma $$(B.E.)products

= (B.E.)H–H + (B.E.)Br–Br –2(B.E)H-Br

= [433 + 192] – 2(364) kJ mol–1

= (625 – 728) kJ mol–1 = –103 kJ mol–1
4
MCQ (Single Correct Answer)

AIPMT 2003

What is the entropy change (in J K$$-$$1 mol$$-$$1) when one mole of ice is converted into water at 0oC? (The enthalpy change for the conversion of ice to liquid water is 6.0 kJ mol$$-$$1 at 0oC).
A
20.13
B
2.013
C
2.198
D
21.98

Explanation

H2O(s) → H2O(l)

$$\Delta $$H = 6.0 kJ mol–1

T = 0 + 273 K = 273 K; $$\Delta $$S = ?

$$\Delta $$S = $${{\Delta H} \over T}$$ = $${{6000} \over {273}}$$ = 21.98 JK–1 mol–1

EXAM MAP

Joint Entrance Examination

JEE Advanced JEE Main

Medical

NEET

Graduate Aptitude Test in Engineering

GATE CE GATE ECE GATE ME GATE IN GATE EE GATE CSE GATE PI