Question

Is the following reaction classified as endothermic or exothermic? Why?

2012(8) + 7O2(g) + 130 kcal -> 2O2(g)
a. Endothermic, because the heat is given as a reactant.
b. Endothermic, because the heat is given as a product.
c. Exothermic, because the heat is given as a reactant.

Answer 1

In an exothermic reaction, heat is listed as a product because it is released during the reaction. In endothermic reactions, heat is listed as a reactant, as it is absorbed to drive the reaction.

Step-by-step explanation:

To determine whether the reaction is endothermic or exothermic, we need to look at where the heat is placed in the reaction equation.

An exothermic reaction releases heat as part of the reaction, which means heat is listed on the product side of the equation. An example of this is:

• 2H₂(g) + O₂(g) → 2H₂O(l) + 135 kcal

Here, the heat is given off by the reaction as a product, indicating that the reaction is exothermic.

Conversely, an endothermic reaction absorbs heat, which means heat is listed on the reactant side of the equation. An example is:

• N₂(g) + O₂(g) + 45 kcal → 2NO(g)

In this case, energy is required for the reaction to proceed, so it is consumed or absorbed, signifying an endothermic reaction.