Chemistry Class-11: Chapter –6. Thermodynamics Part – 2

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Question: 8

The pressure-volume work for an ideal gas can be calculated by using the expression The work can also be calculated from the by using the area under the curve within the specified limits. When an ideal gas is compressed (a) reversibly or (b) irreversibly from volume to . Choose the correct option.

(i)

(ii)

(iii)

(iv)

Answer:

(ii)

Justification: Area under the curve is always more in irreversible compression as can be seen from Fig. 6.5 (a) and (b).

Area under the curve

Reversible vs Irreversible

Question: 9

The entropy change can be calculated by using the expression ΔS = rev q When water freezes in a glass beaker, choose the correct statement amongst the following :

(i) (system) decreases but (surroundings) remains the same.

(ii) (system) increases but (surroundings) decreases.

(iii) (system) decreases but (surroundings) increases.

(iv) (system) decreases and (surroundings) also decreases.

Answer: (iii)

Justification: Freezing is exothermic process. The heat released increases the entropy of surrounding.

Question: 10

On the basis of thermochemical equations (a), (b) and (c), find out which of the algebric relationships given in options (i) to (iv) is correct.

(a)

(b)

(c)

(i)

(ii)

(iii)

(iv)

Answer: (iii)

Question: 11

Consider the reactions given below. On the basis of these reactions find out which of the algebric relations given in options (i) to (iv) is correct?

(a)

(b)

(i)

(ii)

(iii)

(iv)

Answer: (iii)

Justification: Same bonds are formed in reaction (a) and (b) but bonds between reactant molecules are broken only in reaction (b).

Question: 12

The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound

(i) Is always negative

(ii) Is always positive

(iii) May be positive or negative

(iv) Is never negative

Answer: (iii)

Question: 13

Enthalpy of sublimation of a substance is equal to

(i) Enthalpy of fusion + enthalpy of vapourisation

(ii) Enthalpy of fusion

(iii) Enthalpy of vapourisation

(iv) Twice the enthalpy of vapourisation

Answer: (i)

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