State which of the following statements is true ?

1. First law of thermodynamics is not adequate in predicting the direction of the process.

2. In an exothermic reaction, the total enthalpy of the products is greater than that of reactants.

3. The standard enthalpy of diamond is zero at 298 K and 1 atm pressure.

4. It is possible to calculate the value of $∆H$ for the reaction $H_2\left(g\right)+B{r}_2\left(l\right)\to 2HBr\left(g\right)$ from the bond enthalpy data.

If $∆\mathrm{H}$ of a reaction is 100 kJ mol^-1, then the activation energy for the forward reaction must be

1. Greater than 100 kJ mol^-1

2. Less than 100 kJ mol^-1

3. Equal to 100 kJ mol^-1

4. None of the above.

The intermediate SiH₂ is formed in the thermal decomposition of silicon hydrides. Calculate $∆H_f^{\circ }$ of SiH₂ given the following reactions

$S{i}_2{H}_6\left(g\right)+H_2\left(g\right)\to 2Si{H}_4\left(g\right); ∆H^{\circ }=-11.7 kJ/mol$
$Si{H}_4\left(g\right)\to Si{H}_2\left(g\right)+H_2\left(g\right); ∆H^{\circ }=+239.7 kJ/mol$
$∆H_f, S{i}_2{H}_6\left(g\right)=+80.3 kJ mo{l}^{-1}$

1. 353 kJ/mol

2. 321 kJ/mol

3. 198 kJ/mol

4. 274 kJ/mol

A certain vessel X has water and nitrogen gas at a total pressure of 2 atm. and 300 K. All the contents of the vessel are transferred to another vessel Y having half the capacity of the vessel X. The pressiure of N₂ in this vessel was 3.8 atm. at 300 K. The vessel Y is heated to 320 K and the total pressure observed was 4.32 atm. Calculate the enthalpy of vapourisation of water assuming it to be independent of temperature. Also assume the volume occupied by the gases in a vessel is equal to the volume of the vessel.

1. 39.637 kJ mol^-1

2. 19.531 kJ mol^-1

3. 396.37 kJ mol^-1

4. 3.9127 kJ mol^-1

For a reaction, $A+B\to AB, ∆c_P$ is given by the equation $40+5\times {10}^{-3} T J{K}^4$ in the temperature range 300-600 K. The enthalpy of the reaction at 300 K is -25.0 KJ. Calculate the enthalpy of the reaction at 450 K.

1. -10.12 kJ

2. -28.32 kJ

3. -18.72 kJ

4. -8.21 kJ

Given that the heat of combustion of ethylene at 17°C and constant volume is -332.19 kcal, what is the value of the heat of combustion at constant pressure, assuming water is in the liquid state?

1. -131.25 k cals

2. -412.23 k cals

3. -534.12 k cals

4. -333.35 k cals

The enthalpies of the following reactions are shown alongwith.

$\frac{1}{2}{H}_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to OH\left(g\right) ; ∆H=42.09 kJ mo{l}^{-1}$
$H_2\left(g\right)\to 2H\left(g\right); ∆H=435.89 kJ mo{l}^{-1}$
$O_2\left(g\right)\to 2O\left(g\right); ∆H=495.05 kJ mo{l}^{-1}$

Calculate the O-H bond energies for the hydroxyl radical.

1. 223.18 kJ mol^-1

2. 423.38 kJ mol^-1

3. 513.28 kJ mol^-1

4. 113.38 kJ mol^-1

The bond dissociation enthalpy of gaseous H₂, Cl₂ and HCl are 435, 243 and 431 kJ mol^-1, respectively. Calculate the enthalpy of formation of HCl gas.

1. -92 kJ mol^-1

2. -82 kJ mol^-1

3. -21 kJ mol^-1

4. -55 kJ mol^-1

The standard enthalpy of combustion at ${25}^{\circ }C$ of hydrogen, cyclohexene (C₆H₁₀) and cyclohexane (C₆H₁₂) are -241, -3800 and -3920 kJ mol^-1, respectively. Calculate the standard enthalpy of hydrogenation of cyclohexene.

1. -131 kJ mol^-1

2. -155 kJ mol^-1

3. -167 kJ mol^-1

4. -121 kJ mol^-1

A gas mixture consisting of 3.67 litres of ethylene and methane on complete combustion at ${25}^{\circ }C$ produces 6.11 litres of CO₂. Find out the amount of heat evolved on burning one litre of the gas mixture. The heats of combustion of ethylene and methane are -1423 and -891 kJ mol^-1, respectively, at ${25}^{\circ }C$.

1. 30.88 kJ

2. 20.28 kJ

3. 50.88 kJ

4. 60.18 kJ