Calculate Hrxn for the reaction below.
2 NOCl(g) N2(g) + O2(g) + Cl2(g)
You are given the following set of reactions.
1/2 N2(g) + 1/2 O2(g) NO(g) H = 90.30 kJ
NO(g) + 1/2 Cl2(g) NOCl(g) H = -38.6 kJ
To calculate the enthalpy change (Hrxn) for the given reaction, you can use Hess's law. Hess's law states that the overall enthalpy change of a reaction is independent of the pathway taken and depends only on the initial and final states.
To apply Hess's law, you need to manipulate the given reactions and their enthalpy changes to match the target reaction. Here is the step-by-step process to calculate Hrxn:
Step 1: Reverse the second reaction:
Reverse the second reaction: NOCl(g) -> NO(g) + 1/2 Cl2(g)
Reverse the sign of the enthalpy change: ΔH = +38.6 kJ
Step 2: Multiply the first reaction by 2:
Multiply the first reaction by 2: 2 * [1/2 N2(g) + 1/2 O2(g) -> NO(g)]
Multiply the enthalpy change by 2: ΔH = 2 * 90.30 kJ = 180.60 kJ
Step 3: Add the manipulated reactions together:
Add the manipulated reactions together to obtain the target reaction: 2 NOCl(g) -> N2(g) + O2(g) + Cl2(g)
Add the enthalpy changes together:
ΔHrxn = ΔH1 + ΔH2 = 180.60 kJ + 38.6 kJ = 219.20 kJ
Therefore, the enthalpy change (Hrxn) for the given reaction, 2 NOCl(g) -> N2(g) + O2(g) + Cl2(g), is 219.20 kJ.