Consider the gas phase reaction
NO + (1/2) O₂ NO₂for which ΔH° = -57.0 kJ and K = 1.5 × 10⁶ at 25°C.
-Calculate ΔH° at 25°C for the following reaction:
2NO + O₂ 2NO₂

Question

Consider the gas phase reaction NO + (1/2)O 2 NO 2 for which ΔH° = -57.0 kJ and K = 1.5 × 10 6 at 25°C. -Calculate ΔH° at 25°C for the following reaction: 2NO + O₂ 2NO₂

Quizplus · Accepted Answer

The reaction given in the problem is: 
NO + (1/2)O2 -> NO2
ΔH° = -57.0 kJ 
K = 1.5 × 10^16 at 25°C

The reaction we are asked to calculate ΔH° for is: 
2NO + O2 -> 2NO2

We can use Hess's law to solve this problem.

Step 1: Reverse the given reaction 
NO2 -> NO + (1/2)O2
ΔH° = +57.0 kJ

Step 2: Multiply the reversed reaction by 2 
2NO2 -> 2NO + O2
ΔH° = 2(57.0 kJ) = 114 kJ

Step 3: Combine the given reaction and the reversed reaction 
2NO + O2 -> 2NO2 
ΔH° = -57.0 kJ + 114 kJ 
ΔH° = 57.0 kJ

Therefore, the correct answer is choice C (-114 kJ).

Consider the Gas Phase Reaction