If the bond energies of H-H, Br-Br, and H-Br are 433, 192 and 364 kJ mol^-1 respectively, 

the $∆\mathrm{H}°$ for the reaction

H₂(g) + Br₂(g) $\to$2HBr(g) is

1.  -103 kJ               

2. -261 kJ

3. +103 kJ               

4. +261 kJ

One mole of methanol when burnt in O₂ gives out 723 kJ mol^-1 of heat. If one mole of O₂ is used, what will be the amount of heat evolved?

1. 482 kJ
2. 241 kJ
3. 723 kJ               
4. 924 kJ

For a given reaction, if ΔH = 35.5 kJ/mol and ΔS = 83.6 J/K·mol, at what temperature is the reaction spontaneous?
(Assume ΔH and ΔS remain constant 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. Determine the change in internal energy $∆$U of the gas:

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

(1) $∆$S = nRln(p_f/p_i)               

(2) $∆$S = nRln(p_i/p_f)

(3) $∆$S = nRTln(p_f/p_i)             

(4) $∆$S = RTln(p_f/p_i)

Find the thermodynamic condition required for a reaction to be spontaneous at all temperatures.

The heat of combustion of carbon to CO₂ is -393.5 kJ/mol. The enthalpy change (ΔH) upon the

formation of 35.2 g of CO₂ from carbon and oxygen gas is:

1. -315 kJ               

2. +315 kJ             

3. -630 kJ                 

4. -3.15 kJ

For the reaction, X₂O₄(l) $\to$2XO₂(g)

$∆$U = 2.1 kcal, $∆$S = 20 cal K^-1 at 300 K. Hence, $∆$G is

1. 2.7 kcal

2. -2.7 kcal

3. 9.3 kcal

4. -9.3 kcal

Find the reaction for which ΔS° is positive, and ΔG° decreases sharply with an increase in temperature.

1. C(graphite) + 1/2 O₂(g) $\to$CO(g)

2. CO(g) + 1/2 O₂(g)$\to$CO₂(g)

3. Mg(s) + 1/2 O₂(g) $\to$MgO(s)

4. 1/2 C (graphite) + 1/2 O₂(g) $\to$1/2 CO₂(g)

The enthalpy of fusion of water is 1.435 kcal/mol. The molar entropy change for the melting of ice at 0 °C is:

1. 10.52 cal/(mol K)

2. 21.04 cal/(mol K)

3. 5.260 cal/(mol K)

4. 0.526 cal/(mol K)