21.

In the conversion of limestone to lime, CaCO₃(s) → CaO(s) + CO₂(g) the values of ∆Hº and ∆Sº are + 179.1 kJ mol^–1 and 160.2 J/K respectively at 298K and 1 bar. Assuming that ∆Hº and ∆Sº do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is

• 1008 K

• 1200 K

• 845 K

• 845 K

The standard enthalpy of formation (∆_fH^o)  at 298 K for methane, CH₄(g), is –74.8 kJ mol^–1. The additional information required to determine the average energy for C – H bond formation would be

• the dissociation energy of H₂ and enthalpy of sublimation of carbon

• latent heat of vapourization of methane

• the first four ionization energies of carbon and electron gain enthalpy of hydrogen

• the first four ionization energies of carbon and electron gain enthalpy of hydrogen

The enthalpy changes for the following processes are listed below:
Cl₂(g) = 2Cl(g), 242.3 kJ mol^–1
I₂(g) = 2I(g), 151.0 kJ mol^–1
ICl(g) = I(g) + Cl(g), 211.3 kJ mol^–1
I₂(s) = I₂(g), 62.76 kJ mol^–1
Given that the standard states for iodine and chlorine are I₂(s) and Cl₂(g), the standard enthalpy of formation for ICl(g) is

• –14.6 kJ mol^–1

• –16.8 kJ mol^–1

• +16.8 kJ mol^–1

• +16.8 kJ mol^–1

(∆H −∆U) for the formation of carbon monoxide (CO) from its elements at 298 K is
(R = 8.314 J K^–1 mol^–1)

• –1238.78 J mol^–1

• 1238.78 J mol^–1

• –2477.57 J mol^–1

• –2477.57 J mol^–1

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 expressions is true? 

• ∆H = 0

• ∆H = ∆U

• ∆H < ∆U

• ∆H < ∆U

Which one of the following statements is NOT true about the effect of an increase in temperature on the distribution of molecular speeds in a gas?

• The most probable speed increases

• The fraction of the molecules with the most probable speed increases

• The distribution becomes broader

• The distribution becomes broader

If the bond dissociation energies of XY, X₂ and Y₂ (all diatomic molecules) are in the ratio of 1:1:0.5 and ∆f H for the formation of XY is -200 kJ mole^-1. The bond dissociation energy of X₂ will be

• 100 kJ mol^-1

• 800 kJ mol^-1

• 300 kJ mol^-1

• 300 kJ mol^-1

The enthalpies of combustion of carbon and carbon monoxide are -393.5 and -283 kJ mol^-1 respectively. The enthalpy of formation of carbon monoxide per mole is

• 110.5 kJ

• -110.5 kJ

• -676.5 kJ

• -676.5 kJ

Which of the following lines correctly show the temperature dependence of equilibrium constant K, for an exothermic reaction?

• A and D

• A and B

• B and C

• C and D

The combustion of benzene (l) gives CO₂(g) and H₂O(l). Given that heat of combustion of benzene at constant volume is –3263.9 kJ mol^–1 at 250C; the heat of combustion (in kJ mol^–1) of benzene at constant pressure will be (R = 8.314 JK^–1 mol^–1)

• –3267.6

• 4152.6

• –452.46

• 3260