﻿ 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 | Thermodynamics

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# Thermodynamics

#### Multiple Choice Questions

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

180 Views

22.

The standard enthalpy of formation (∆fHo)  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

304 Views

23.

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

511 Views

24.

(∆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

229 Views

25.

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

545 Views

26.

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

163 Views

# 27.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

B.

800 kJ mol-1

XY→ X(g) + Y(g) ; ∆H +a kJ/ mole ............(i)
X2 → 2X; ∆H = +a kJ/mole........(ii)
Y2 → 2Y; ∆H =+0.5a kJ/mole.......(iii)

624 Views

28.

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

223 Views

29.

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

30.

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