`N_(2(g)) + O_(2(g)) to 2N_((g)) - 42.0` kcal

Options

A. exothermic
B. endothermic
C. addition
D. dissociation

Explanation

To determine the type of reaction represented by the equation \( N_2(g) + O_2(g) \rightarrow 2N(g) - 42.0 \, \text{kcal} \), we will analyze the information provided step by step.

### Step 1: Identify the Reaction Type
The reaction involves nitrogen gas (\( N_2 \)) and oxygen gas (\( O_2 \)) reacting to form nitrogen gas (\( N \)). The equation also indicates that 42.0 kcal of heat is released during this process.

### Step 2: Understand Exothermic vs. Endothermic Reactions
- **Exothermic Reaction**: In an exothermic reaction, heat is released to the surroundings. This is indicated by a negative sign in front of the heat value (e.g., \( -42.0 \, \text{kcal} \)).
- **Endothermic Reaction**: In an endothermic reaction, heat is absorbed from the surroundings. This is indicated by a positive sign in front of the heat value (e.g., \( +42.0 \, \text{kcal} \)).

### Step 3: Analyze the Given Reaction
In the given reaction:
\[ N_2(g) + O_2(g) \rightarrow 2N(g) - 42.0 \, \text{kcal} \]
The presence of \( -42.0 \, \text{kcal} \) indicates that heat is being released. This means that the products have lower energy than the reactants, which is characteristic of an exothermic reaction.

### Step 4: Conclusion
Since the reaction releases heat, we can conclude that this is an **exothermic reaction**. Therefore, the correct answer is:
- **Exothermic Reaction**