Question

which of the following statements is true? the overall chemical reaction is exothermic. there are two intermediate reactions in this system. the third intermediate reaction is endothermic. the longest arrow represents the overall chemical reaction.

Explanation:

Step1: Analyze exothermic/endothermic

In a reaction, if $\Delta H_{\text{rxn}}$ (enthalpy change of reaction) has a downward arrow (products have lower energy than reactants), the reaction is exothermic (releases heat). Here, $\Delta H_{\text{rxn}}$ is downward, so check the first option.

Step2: Check intermediate reactions

The diagram has $\Delta H_1$, $\Delta H_2$, $\Delta H_3$ as intermediate steps? Wait, no—count the intermediate reactions. The arrows $\Delta H_1$, $\Delta H_2$, $\Delta H_3$: wait, the first option: exothermic (since $\Delta H_{\text{rxn}}$ is negative, release heat). Let's verify each option:

• "The overall chemical reaction is exothermic": Since $\Delta H_{\text{rxn}}$ arrow is downward (products at lower energy), reaction releases heat → exothermic. Correct.
• "There are two intermediate reactions": The intermediates are $\Delta H_1$, $\Delta H_2$, $\Delta H_3$? Wait, no—three? Wait, the diagram has three arrows ($\Delta H_1$, $\Delta H_2$, $\Delta H_3$) and $\Delta H_{\text{rxn}}$. So intermediate reactions: maybe three? So "two" is wrong.
• "The third intermediate reaction is endothermic": $\Delta H_3$ arrow is downward (energy decrease), so exothermic, not endothermic. Wrong.
• "The longest arrow represents the overall chemical reaction": $\Delta H_2$ (blue upward) looks longest, but $\Delta H_{\text{rxn}}$ is red downward, shorter. So wrong.

Answer:

The overall chemical reaction is exothermic.