Question

Given the balanced equation representing a reaction at 101.3 kPa and 298 K:
N2(g) + 3H2(g) => 2NH3(g) + 91.8 kJ
Which statement is true about this reaction?
(1) It is exothermic and DH equals -91.8 kJ.
(2) It is exothermic and DH equals +91.8 kJ.
(3) It is endothermic and DH equals -91.8 kJ.
(4) It is endothermic and DH equals +91.8 kJ.

Answer 1

On this item, options B, C, and D, should be out since this reaction, 101.3 kPa and 298 K:N2(g) + 3H2(g) => 2NH3(g) + 91.8 kJ is an exothermic reaction. Hence, energy is released as a product and the reaction is exothermic (losing energy) , delta H should be negative which is -91.8kJ. Thus, the answer should be letter A.

Answer 2

Answer: (1) It is exothermic and DH equals -91.8 kJ.

Explanation: $N_2(g)+3H_2(g)\rightarrow 2NH_3(g)+91.8 kJ$

There are two types of reactions in terms of heat:

Endothermic reactions are those reactions in which heat is absorbed by the system and exothermic reactions are those reactions in which heat is released by the system.

As the heat is given on the products side, it means the heat is released in the reaction and thus the reaction is exothermic. The enthalpy change for exothermic reaction is written as negative and the enthalpy change for endothermic reaction is written as positive.