Enthalpy is a state function. It is the sum of the total internal energy of the system and the product of its volume and pressure (H = U + pV). At constant pressure, the heat absorbed by the system is equal to the change in the enthalpy, i.e. 𝚫H. In an exothermic reaction, 𝚫H is negative, i.e. heat is evolved during the reaction and in an endothermic reaction, 𝚫H is positive, i.e. heat is absorbed during the reaction.

1. Which of the following is correct, if a reaction has equal energies of activation for both, forward as well as reverse reactions?

(a) ΔH = ΔG = ΔS = 0

(b) ΔH = 0

(c) ΔG = 0

(d) ΔS = 0

2. Which of the following hold true for a spontaneous reaction at all temperatures?

(a) ΔH < 0 and ΔS < 0

(b) ΔH < 0 and ΔS > 0

(c) ΔH > 0 and ΔS < 0

(d) None of the above

3. What would be the dissociation energy of the H-H bond for the reaction 4H_(g) → 2H_2(g), if the ΔH is – 869.6 kJ?

(a) – 869.6 kJ

(b) – 434.8 kJ

(c) + 217.4 kJ

(d) + 434.8 kJ

4. Change in enthalpy of the system is the heat absorbed at a

(a) constant pressure

(b) constant volume

(c) constant temperature

(d) none

5. Which of the following equations is correct for the enthalpy of the system?

(a) H = – U – pV

(b) H = U + pV

(c) H = U – pV

(d) H = – U + pV

6. The energy required to break a covalent bond is known as

(a) bond energy

(b) bond dissociation energy

(c) bond enthalpy

(d) all of the above

7. The change of enthalpy in an endothermic reaction is

(a) positive

(b) negative

(c) constant

(d) any of the above

8. Change in the internal energy of the system is equal to the heat absorbed at a

(a) constant pressure

(b) constant volume

(c) constant temperature

(d) none

9. When heat is transferred to a system at constant pressure, the enthalpy of the system

(a) increases

(b) decreases

(c) first increases then decreases

(d) first decreases then increases

10. The change of enthalpy in an exothermic reaction is

(a) positive

(b) negative

(c) constant

(d) any of the above

Answer