Thermodynamics

The change in entropy for the fusion of 1 mole of ice is [mp of ice = 273 K, molar enthalpy of fusion for ice= 6.0 kJ mol^-1]

• 11.73 JK^-1 mol^-1

• 18.84 JK^-1 mol^-1

• 21.97 JK^-1 mol^-1

• 24.47 JK^-1 mol^-1

A reaction occurs spontaneously if

• T$∆$S < $∆$H and both $∆$H and $∆$S are +ve

• T$∆$S > $∆$H and both $∆$H and $∆$S are +ve

• T$∆$S = $∆$H and both $∆$H and $∆$S are +ve

• T$∆$S > $∆$H and $∆$H is +ve and $∆$S is - ve

Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction?

• Exothermic and decreasing disorder

• Endothermic and increasing disorder

• Exothermic and increasing disorder

• Endothermic and decreasing disorder

The absolute enthalpy of neutralisation of the reaction

MgO(s) + 2HCl(aq) $\to$ MgCl₂(aq) + H₂O(l)

will be

• less than - 57.33 kJ mol^-1

• - 57.33 kJ mol^-1

• greater than-- 57.33 kJ mol^-1

• 57.33 kJ mol^-1

Which of the following have highest electron affinity?

• F

• Cl

• N

• O

The enthalpy of combustion at 25°C of H₂, cyclohexane (C₆H₁₂) and cyclohexene (C₆H₁₀) are -241, -3920 and -3800 kJ/mol respectively. The heat of hydrogenation of cyclohexene is :

• -121 kJ/mol

• +121 kJ/mol

• -242 kJ/mol

• +242 kJ/mol

The entropy values (in JK^-1mol^-1) of H₂ (g) = 130.6, Cl₂ (g) = 223.0 and HCl (g) = 186. 7 at 298 K and 1 atm pressure. Then entropy change for the reaction :

H₂ ( g)+ Cl₂ (g) $\to$ 2HCl (g) is:

• +540.3

• +727.3

• -166.9

• +19.8

Consider the respective enthalpy for the following reactions:

$$\begin{gathered} \left(\mathrm{I}\right) {\mathrm{NH}}_3\left(\mathrm{g}\right) + 3{\mathrm{Cl}}_2 \left(\mathrm{g}\right) \rightleftharpoons {\mathrm{NCl}}_3 \left(\mathrm{g}\right) + 3\mathrm{HCl} \left(\mathrm{g}\right); -{\mathrm{\Delta H}}_1 \\ \left(\mathrm{II}\right) {\mathrm{N}}_2\left(\mathrm{g}\right)+ 3{\mathrm{H}}_{2 }\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{NH}}_{3 }\left(\mathrm{g}\right); -{\mathrm{\Delta H}}_2 \\ \left(\mathrm{III}\right) {\mathrm{H}}_2 \left(\mathrm{g}\right) + {\mathrm{Cl}}_2 \left(\mathrm{g}\right) \rightleftharpoons 2\mathrm{HCl} \left(\mathrm{g}\right); {\mathrm{\Delta H}}_3 \end{gathered}$$

$\mathrm{The} \mathrm{enthalpy} \mathrm{of} \mathrm{formation} \mathrm{of} {\mathrm{NCl}}_3 \left(\mathrm{g}\right) \mathrm{in} \mathrm{terms} \mathrm{of} {\mathrm{\Delta H}}_1 , {\mathrm{\Delta H}}_{2 ,} {\mathrm{\Delta H}}_3 \mathrm{is}:$

• ${\mathrm{\Delta H}}_{\mathrm{f}}= -{\mathrm{\Delta H}}_1 +\frac{{\mathrm{\Delta H}}_2}{2} - \frac{3}{2} {\mathrm{\Delta H}}_3$

• ${\mathrm{\Delta H}}_{\mathrm{f}}= {\mathrm{\Delta H}}_1 +\frac{{\mathrm{\Delta H}}_2}{2} - \frac{3}{2} {\mathrm{\Delta H}}_3$

• ${\mathrm{\Delta H}}_{\mathrm{f}}= -{\mathrm{\Delta H}}_1 - \frac{{\mathrm{\Delta H}}_2}{2} - \frac{3}{2} {\mathrm{\Delta H}}_3$

• None of the above

The entropy will be positive in which of the following reaction change.

• H₂(g) + I₂ (g) $\leftrightharpoons$ 2HI (g)

• HCl(g) + NH₃ (g) $\leftrightharpoons$ N₂O(g) + 2H₂O(g)

• NH₄NO₃(s)$\leftrightharpoons$N₂O(g) + 2H₂O(g)

• MgO(s) + H₂(g) $\leftrightharpoons$ Mg(s) + H₂O(l)

C_(dia) + O₂ $\to$ CO₂; $∆\mathrm{H}$ = - 395.4 kJ/ mol

C_(gr) + O₂ $\to$CO₂; $∆$H   = - 393.5 kJ/ mol

C_(gr) $\to$C_(dia); $∆$H = ?

• -3.8

• -1.9

• +3.8

• +1.9