The bond dissociation energies of $X_2 , Y_2$ and XY are in the ratio of 1 : 0.5 : 1. ∆H for the formation of XY is –200 kJ mol^–1. The bond dissociation energy of X₂ will be

For a given reaction, $∆$H =35.5 kJ mol^-1 and $∆$S = 83.6JK^-1 mol^-1. The reaction is spontaneous at:
(Assume that $∆$H and $∆$S do not vary with temperature)

A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy $∆$U of the gas in joules will be

(1) 1136.25 J

(2) - 500 J

(3) - 505 J

(4) + 515 J

For a given reaction, ∆H = 35.5 kJ mol^–1 and ∆S = 83.6 J K^–1 mol^–1. The reaction is spontaneous at:
(Assume that ∆H and ∆S  do not vary with temperature)
1. T > 425K
2. All temperatures
3. T > 298K
4. T < 425K

A gas is allowed to expand in a well-insulated container against a constant external pressure of 2.5atm from an initial volume of 2.50 L to a final volume of 4.50L. The change in internal energy U of the gas in joules will be:
1. –500J
2. –505J
3. –506J
4. –508J

The correct thermodynamic conditions for the spontaneous reaction at all temperatures is

$\left(\mathrm{a}\right) ∆\mathrm{H}>0 \mathrm{and} ∆\mathrm{S}<0$
$\left(\mathrm{b}\right) ∆\mathrm{H}<0 \mathrm{and} ∆\mathrm{S}>0$
$\left(\mathrm{c}\right) ∆\mathrm{H}<0 \mathrm{and} ∆\mathrm{S}<0$
$\left(\mathrm{d}\right) ∆\mathrm{H}<0 \mathrm{and} ∆\mathrm{S}=0$

For a sample of a perfect gas when its pressure is changed isothermally from P_i to P_f, the entropy change is given by:

1. $∆\mathrm{s}=\mathrm{nR}$ $\mathrm{In}$ $\left(\frac{{\mathrm{p}}_{\mathrm{f}}}{{\mathrm{p}}_{\mathrm{i}}}\right)$

2. $∆\mathrm{s}=\mathrm{nR}$ $\mathrm{In}$ $\left(\frac{{\mathrm{p}}_{\mathrm{i}}}{{\mathrm{p}}_{\mathrm{f}}}\right)$

3. $∆\mathrm{s}=\mathrm{nRT}$ $\mathrm{In}$ $\left(\frac{{\mathrm{p}}_{\mathrm{f}}}{{\mathrm{p}}_{\mathrm{i}}}\right)$

4. $∆\mathrm{s}=\mathrm{RT}$ $\mathrm{In}$ $\left(\frac{{\mathrm{p}}_{\mathrm{i}}}{{\mathrm{p}}_{\mathrm{f}}}\right)$