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Thermodynamics

Multiple Choice Questions

401.

Choose the reaction in which $∆$ H is not equal to $∆$ U

C(graphite) + O₂(g) → CO₂(g)
C₂H₄(g) + H₂(g) → C₂H₆(g)
2C(graphite) + H₂(g) → C₂H₂(g)
H₂(g) + I₂(g) → 2HI(g)

402.
The standard enthalpies of combustion of C₆H₆ (l), C_(graphite) and H₂ (g) are respectively -3270 kJ mol^-1, -394 kJ mol^-1 and -286 kJ mol^-1. What is the standard enthalpy of formation of C₆H₆ (l) in kJ mol^-1?

-48

+48

-480

+480

+48

Given,

(i) C₆H₆ + $\frac{15}{2}$ O₂ → 6CO₂ + 3H₂O; $∆$ H = -3270 kJ mol^-1

(ii) C_(graphite) + O₂ → CO₂; $∆$ H = -394 kJ mol^-1

(iii) H₂ + $\frac{1}{2}$ O₂ → H₂O; $∆$ H = -286 kJ mol^-1

On multiplying equation (ii) by 6 and equation (iii) by 3, we get,

(iv) 6C (s) + 6O₂ → 6CO₂; $∆$ H = -394 × 6 kJ mol^-1 = -2364 kJ mol^-1

(v) 3H₂ + $\frac{3}{2}$ O₂ → 3H₂O; $∆$ H = -286 × 3 kJ mol^-1 = -858 kJ mol^-1

On inverting equation (i), we get,

(vi) 6CO₂ + 3H₂O → C₆H₆ + $\frac{15}{2}$ O₂; $∆$ H = +3270 kJ mol^-1

On adding equation (iv), (v) and (vi),

6C (s) + 3H₂ → C₆H₆; $∆$ H = +3270 + (-2364 - 858) = + 48 kJ mol^-1

Thus, the standard enthalpy of formation of C₆H₆ is +48 kJ mol^-1.

403.

What is the amount of work done when 0.5 mole of methane, CH₄(g), is subjected to combustion at 300 K? (Given, R=8.314JK^-1 mol^-1)

-2494 J
-4988 J
+ 4988 J
+ 2494 J

404.

In the reaction; A₂(g) + 3B₂(g) → 2AB₃(g), the standard entropies in (JK^-1 mol^-1) of A₂(g), B₂(g) and AB₃(g) are respectively 190, 130 and 195 and the standard enthalpy change for the reaction is -95 kJ mol^-1. The temperature (in K) at which the reaction attains equilibrium is (assuming both the standard entropy change and standard enthalpy change for this reaction are constant over a wide range of temperature)

405.

Calculate the standard enthalpy change (in kJ mol^-1) for the reaction

H₂(g) + O₂(g) → H₂O₂(g)

Given that bond enthalpies of H-H, O=O, O-H and O-O (in KJ mol^-1) are respectively 438, 498, 464 and 138.

-130
-65
+130
-334

406.

According to the first law of thermodynamics which of the following quantities represents the change in a state function?

q_rev + W_rev
q_rev
q_rev - W_rev
q_rev / W_rev

407.

If the activation energy for the forward reaction is 150 kJ mol^-1 and that of the reverse reaction is 260 kJ mol^-1, what is the enthalpy change for the reaction?

410 kJ mol^-1
110kJ mol^-1
-110 kJ mol^-1
-410 kJ mol^-1

408.

When 0.2 g of 1-butanol was burnt in a suitable apparatus, the heat evolved was sufficient to raise the temperature of 200 g water by 5°C. The enthalpy of combustion of 1-butanol in kcal mol^-1 will be