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Based on the enthalpy changes given for the reactions, which reactions are endothermic?

1. [tex]\( 2H_2O \rightarrow 2H_2 + O_2, \Delta H = 484 \, kJ \)[/tex]
2. [tex]\( C + O_2 \rightarrow CO_2, \Delta H = -394 \, kJ \)[/tex]
3. [tex]\( H_2 + Br_2 \rightarrow 2HBr, \Delta H = -73 \, kJ \)[/tex]
4. [tex]\( 2NH_3 \rightarrow N_2 + 3H_2, \Delta H = 92 \, kJ \)[/tex]

Sagot :

GinnyAnswer
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]
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