Calculate the enthalpy change for the reaction

Question

N2 (g) + 202 (g) —> 2NO2 (g)  △Hrxn = ____kJ

Give the following information:

N2 (g) + O2 (g) —> 2NO(g) △Hrxn = -181 kJ

2NO(g) + O2 (g) —> 2NO2 (g) △Hrxn = -115 kJ

Answer 1

Hess's Law:

Given:

Eq.(1). N2 (g) + O2 (g) —> 2NO(g) △Hrxn = -181 kJ

Eq.(2). 2NO(g) + O2 (g) —> 2NO2 (g) △Hrxn = -115 kJ

Target equation:

N2 (g) + 202 (g) —> 2NO2 (g) △Hrxn = ____kJ

Procedure:

copy eq.(1): N2 (g) + O2 (g) —> 2NO(g) ... △Hrxn = -181 kJ

copy eq.(2): 2NO(g) + O2 (g) —> 2NO2 (g) ... △Hrxn = -115 kJ

Add then together and combine/cancel like terms:

N2 (g) + O2 (g) + 2NO(g) + O2 (g) —> 2NO(g) + 2NO2 (g)

N2(g) + 2O2(g) —> 2NO2(g) = TARGET EQUATION

To get ∆H, add the ∆H of each reaction:

∆H = -181 kJ + -115 kJ

∆H = -296 kJ