To determine which reactions are endothermic, we need to look at the change in enthalpy ([tex]\(\Delta H\)[/tex]) for each reaction. An endothermic reaction is characterized by a positive [tex]\(\Delta H\)[/tex] value, meaning the reaction absorbs heat from the surroundings.
Here are the given reactions with their respective [tex]\(\Delta H\)[/tex] values:
1. [tex]\(2 H_2O \rightarrow 2 H_2 + O_2\)[/tex], [tex]\(\Delta H = 484\)[/tex] kJ
2. [tex]\(C + O_2 \rightarrow CO_2\)[/tex], [tex]\(\Delta H = -394\)[/tex] kJ
3. [tex]\(H_2 + Br_2 \rightarrow 2 HBr\)[/tex], [tex]\(\Delta H = -73\)[/tex] kJ
4. [tex]\(2 NH_3 \rightarrow N_2 + 3 H_2\)[/tex], [tex]\(\Delta H = 92\)[/tex] kJ
Now, let's identify which reactions are endothermic by checking if [tex]\(\Delta H\)[/tex] is positive:
1. [tex]\(2 H_2O \rightarrow 2 H_2 + O_2\)[/tex]
- [tex]\(\Delta H = 484\)[/tex] kJ (positive [tex]\(\Delta H\)[/tex])
- This reaction is endothermic.
2. [tex]\(C + O_2 \rightarrow CO_2\)[/tex]
- [tex]\(\Delta H = -394\)[/tex] kJ (negative [tex]\(\Delta H\)[/tex])
- This reaction is exothermic, not endothermic.
3. [tex]\(H_2 + Br_2 \rightarrow 2 HBr\)[/tex]
- [tex]\(\Delta H = -73\)[/tex] kJ (negative [tex]\(\Delta H\)[/tex])
- This reaction is exothermic, not endothermic.
4. [tex]\(2 NH_3 \rightarrow N_2 + 3 H_2\)[/tex]
- [tex]\(\Delta H = 92\)[/tex] kJ (positive [tex]\(\Delta H\)[/tex])
- This reaction is endothermic.
From this analysis, the reactions that are endothermic are:
- [tex]\(2 H_2O \rightarrow 2 H_2 + O_2\)[/tex]
- [tex]\(2 NH_3 \rightarrow N_2 + 3 H_2\)[/tex]
So, the correct answers are:
[tex]\[2 H_2O \rightarrow 2 H_2 + O_2\][/tex]
[tex]\[2 NH_3 \rightarrow N_2 + 3 H_2\][/tex]
