Standard enthalpies of formation of O₃, CO₂, NH₃ and HI are 142.2, -393.2,- 46.2 and 25.9 kJ mol^-1 respectively. Decreasing order of their stability is

• HI > NH₃ > CO₂ > O₃

• NH₃ > CO₂ > HI > O₃

• CO₂ > NH₃ > HI > O₃

• O₃ > HI > NH₃ > CO₂

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

173.

The standard enthalpy of vapourisation Δ_vap H° for water at 100°C is 40.66 kJ mol^-1. The internal energy of vapourisation of water 100°C (in kJ mol^-1) is (assume water vapour to behave like an ideal gas).

• + 4376

• +40.66

• +37.56

• None of these

Which one of the following statements is true?

• $∆$E ia always greater than $∆$H

• $∆$E is always less than $∆$H

• $∆$E may be lesser or greater or equal to $∆$H

• $∆$E is always proportional to $∆$H

The intensive property among these quantities is

• enthalpy

• mass/ volume

• mass

• volume

If the adsorption of a gas on solid metal surface is spontaneous and exothermic, then

• H increases

• S increases

• G increases

• S decreases

30g of Mg and 30g of oxygen are reacted and the residual mixture contains

• 45 g of MgO and 15 g of O₂

• 50 g of MgO and 10 g of O₂

• 60 g of MgO only

• 40 g of MgO and 20 g of O₂

Compounds with high heat of formation are less stable because

• high temperature is required to synthesise them

• molecules of such compounds are distorted

• it is difficult to synthesise them

• energy rich state leads to instability

Enthalpy of formation of HF and HCl are -161 kJ and -92 kJ respectively. Which of the following statements is incorrect?

• HCl is more stable than HF

• HF and HCl are exothermic compounds

• The affinity of fluorine to hydrogen is greaterthan the affinity of chlorine to hydrogen

• HF is more stable than HCl

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