Question

\( C(s) + O_2(g) \rightarrow CO_2(g) \quad \Delta H = -94 \, \text{kcal} \)
\( 2CO(g) + O_2(g) \rightarrow 2CO_2(g) \quad \Delta H = -135.2 \, \text{kcal} \)
The heat of formation of \( CO(g) \) is:

• A. -26.4 kcal
• B. 41.2 kcal
• C. 26.4 kcal
• D. 229.2 kcal

Hint:

Use Hess’s law by manipulating equations to get desired reaction.

Answer 1

The Correct Option is A

Concept: Use Hess’s law.

Step 1: Given reactions.
\[ (1)\; C + O_2 \rightarrow CO_2 \quad (-94) \] \[ (2)\; 2CO + O_2 \rightarrow 2CO_2 \quad (-135.2) \]

Step 2: Divide (2) by 2.
\[ CO + \frac{1}{2}O_2 \rightarrow CO_2 \quad (-67.6) \]

Step 3: Subtract.
\[ C + \frac{1}{2}O_2 \rightarrow CO \] \[ \Delta H = -94 - (-67.6) = -26.4 \, \text{kcal} \]