To determine which reaction is exothermic, we need to identify which reaction releases energy. An exothermic reaction is characterized by the release of energy, usually in the form of heat, meaning that energy will be a product in the reaction (on the right side of the equation).
Let's analyze each reaction step-by-step:
1. First Reaction:
[tex]\[
CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O + 891 \text{ kJ}
\][/tex]
- In this reaction, 891 kJ of energy appears on the product side, indicating that energy is released. This suggests that the reaction is exothermic.
2. Second Reaction:
[tex]\[
NH_4NO_3 + H_2O + 25 \text{ kJ} \rightarrow NH_4^+(aq) + NO_3^-(aq)
\][/tex]
- Here, 25 kJ of energy is on the reactant side, indicating that energy is absorbed. Hence, this reaction is endothermic.
3. Third Reaction:
[tex]\[
2 H_2O + 286 \text{ kJ} \rightarrow 2 H_2 + O_2
\][/tex]
- In this case, 286 kJ of energy is on the reactant side, showing that energy is absorbed. This reaction is also endothermic.
4. Fourth Reaction:
[tex]\[
N_2 + O_2 + 181 \text{ kJ} \rightarrow 2 NO
\][/tex]
- Similarly, 181 kJ of energy is on the reactant side, which means that energy is absorbed. This reaction is endothermic as well.
After analyzing all the reactions, it's clear that the first reaction [tex]\( CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O + 891 \text{ kJ} \)[/tex] is exothermic because it releases energy. The correct exothermic reaction is:
[tex]\[
\boxed{1}
\][/tex]
