Question

For H₂O₂(g), find the value of ΔH°f.

a) Exothermic
b) Endothermic
c) Zero
d) Cannot be determined

Answer 1

In the given chemical reactions, the enthalpy change can be determined by comparing the coefficients and the given enthalpy values. The first reaction is exothermic because heat is released, while the second reaction is endothermic because heat is absorbed.

Step-by-step explanation:

The enthalpy change of a reaction can be determined by examining the energy difference between the reactants and products. If the enthalpy change is negative, it is considered exothermic, meaning heat is released. If the enthalpy change is positive, it is considered endothermic, meaning heat is absorbed. In the given chemical reactions, the enthalpy change can be determined by comparing the coefficients and the given enthalpy values.

1. a. For the reaction 2H₂(g) + O₂(g) → 2H₂O(l) + 135 kcal, the enthalpy change is -135 kcal. This indicates that heat is released, so it is an exothermic reaction.
2. b. For the reaction N₂(g) + O₂(g) → 2NO(g), the enthalpy change is 45 kcal. Since the value is positive, it indicates that heat is absorbed, so it is an endothermic reaction.