Question

Given the following data, i. 2NO2(g) → N2(g) + 2O2(g) DH1 = –67.8 kJ ii. 2NO2(g) → 2NO(g) + O2(g) DH2 = 113 kJ Determine the DH (in kJ) for the reaction: N2(g) + O2(g) → 2NO(g)

Answer 1

The enthalpy change for the reaction N2(g) + O2(g) → 2NO(g) is calculated using Hess's Law by reversing and combining given reactions. The final enthalpy change for the target reaction is found to be +180.8 kJ.

Step-by-step explanation:

To determine the enthalpy change (ΔH) in kJ for the reaction N2(g) + O2(g) → 2NO(g), we can use Hess's Law which allows us to add or subtract given chemical equations to yield the target equation. We are given two reactions with their respective enthalpy changes:

i. 2NO2(g) → N2(g) + 2O2(g) ΔH1 = –67.8 kJ

ii. 2NO2(g) → 2NO(g) + O2(g) ΔH2 = 113 kJ

To obtain the target equation, we need to reverse the first reaction, and then combine it with the second reaction:

Reverse Reaction i. N2(g) + 2O2(g) → 2NO2(g) ΔH1' = +67.8 kJ (Reverse the sign of ΔH)

Add Reaction ii. 2NO2(g) → 2NO(g) + O2(g) ΔH2 = 113 kJ (as given)

Now, cancel out the common species (2NO2) on both sides and add the enthalpy changes. The resulting equation is the target equation and its enthalpy change is the sum of enthalpy changes from the two modified steps:

N2(g) + O2(g) → 2NO(g) ΔH = ΔH1' + ΔH2 = +67.8 kJ + 113 kJ = +180.8 kJ

The enthalpy change for the reaction N2(g) + O2(g) → 2NO(g) is 180.8 kJ.