Thermodynamics

First and second ionisation enthalpies of Mg are 737. 76 and 1450.73 J mol^-1 respectively. The energy required to convert all the atoms of magnesium to magnesium ions present in 24g of magnesium vapours is

• 24 kJ

• 2.188 kJ

• 12 kJ

• 4.253 kJ

The enthalpy of reaction,

${\mathrm{H}}_2\left(\mathrm{g}\right) +\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right) \to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right) \mathrm{is}\hspace{0.17em}∆{\mathrm{H}}_1 \mathrm{and} \mathrm{that} \mathrm{of} H_2\left(\mathrm{g}\right) +\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right) \to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \mathrm{is}\hspace{0.17em}∆{\mathrm{H}}_2.\mathrm{Then}$

• ΔH₁ < ΔH₂

• ΔH₁ + ΔH₂ = 0

• ΔH₁ > ΔH₂

• ΔH₁ = ΔH₂

Molar heat of vaporisation of a liquid is 6 kJ mol^-1. If the entropy change is 16 J mol^-1 K^-1, the boiling point of the liquid is:

• 375°C

• 375 K

• 273 K

• 102°C

Consider the reaction,

N₂ + 3H₂ → 2NH₃

carried out at constant temperature and pressure. If $∆$H and $∆$U are the enthalpy and internal energy changes for the reaction, which of the following expression is true?

• $∆\mathrm{H} > ∆\mathrm{U}$

• $∆\mathrm{H} <∆\mathrm{U}$

• $∆\mathrm{H} = ∆\mathrm{U}$

• $∆$H = 0

If standard enthalpies of formation of CaCl (s) (hypothetical) and that of CaCl₂ (s) are -188 J mol^-1 and -795 kJ mol^-1 respectively, calculate the value of standard heat of reaction for the following  disproportionation reaction

2CaCl (s) → CaCl₂ (s) + Ca (s)

• -607 kJ mol^-1

• +607 kJ mol^-1

• -419 kJ mol^-1

• +419 kJ mol^-1

For the reaction,

A (g) + 2B (g) → 2C (g) + 3D (g)

the change of enthalpy at 27°C is 19 kcal. The value of $∆$E is

• 21.2 kcal

• 17.8 kcal

• 18.4 kcal

• 20.6 kcal

If  H_f (H₂O) is -286.20 kJ mol^-1, then  H${}_{\mathrm{f}}^{°}$  (OH^-) is

• -228.88 kJ mol^-1

• +228.88 kJ mol^-1

• -343.52 kJ mol^-1

• +343.52 kJ mol^-1

1 mole of gas occupying 3 L volume is expanded against a constant external pressure of 1 atm to a volume of 15 L. The work done by a system is equal to

• -1.215 × 10³ J

• -12.15 × 10³ J

• +1.215 × 10³ J

• +12.15 × 10³ J

Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non-expansion work is zero)

• Isothermal process : q = -w

• Cyclic process : q = -w

• Isochoric process : $∆\mathrm{U}$ = q

• Adiabatic process : $∆\mathrm{U}$ = -w