Question

Compare the following combustion reactions:

Ch4 (methane) + O2 → CO2 + H2O
C2H6 (ethane) + O2 → CO2 + H2O
Is this endothermic or exothermic?
Which reaction releases more energy? How do you know?
Which reaction has more potential energy? How do you know?

Answer 1

Exothermic reactions release energy and result in products with less potential energy than the reactants, while endothermic reactions absorb energy, leading to products with more potential energy. The difference is seen in the energy notations for the reactions provided, with exothermic reactions showing energy release and endothermic showing energy requirement.

Step-by-step explanation:

The chemical reactions mentioned can be compared in terms of energy changes. Exothermic reactions release energy, typically in the form of heat, indicating that the sum of energy stored in the bonds of the reactants is higher than that of the products. This means that the potential energy decreases as the reaction proceeds. An example is the combustion of methane:

• CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + 213 kcal

Here, the reaction releases 213 kcal, indicating it's exothermic with products having less potential energy than reactants.

Conversely, endothermic reactions absorb energy:

• N2(g) + O2(g) + 45 kcal → 2NO(g)

This reaction requires an input of 45 kcal, showing that it's endothermic with products having higher potential energy.

All chemical reactions require activation energy to break bonds in the reactants before new bonds can form in the products. The balance between the energy needed to break the bonds and the energy released from forming new bonds determines whether a chemical reaction is endothermic or exothermic.