To determine which of the given reactions is exothermic, we'll first review the concepts of exothermic and endothermic reactions.
1. Exothermic Reactions: These reactions release energy, often in the form of heat, and the energy released is indicated on the product side of the reaction equation.
2. Endothermic Reactions: These reactions absorb energy, and the energy required is indicated on the reactant side of the reaction equation.
Let's analyze each reaction to identify whether it is exothermic or endothermic:
1. Reaction 1:
[tex]\[
CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O + 891 \, \text{kJ}
\][/tex]
In this reaction, 891 kJ of energy is produced as a product. This indicates that energy is released during the reaction, making it an exothermic reaction.
2. Reaction 2:
[tex]\[
NH_4NO_3 + H_2O + 25 \, \text{kJ} \rightarrow NH_4^+ (aq) + NO_3^- (aq)
\][/tex]
Here, 25 kJ of energy is needed as a reactant. This means that the reaction absorbs energy, making it an endothermic reaction.
3. Reaction 3:
[tex]\[
2 H_2O + 286 \, \text{kJ} \rightarrow 2 H_2 + O_2
\][/tex]
In this reaction, 286 kJ of energy is absorbed as a reactant. This indicates that the reaction is endothermic.
4. Reaction 4:
[tex]\[
N_2 + O_2 + 181 \, \text{kJ} \rightarrow 2 NO
\][/tex]
In this case, 181 kJ of energy is required as a reactant. This means the reaction absorbs energy, making it endothermic.
Based on the analysis, the reaction that is exothermic is:
[tex]\[
CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O + 891 \, \text{kJ}
\][/tex]
Therefore, the exothermic reaction is Reaction 1.
