Question

Consider the following set of reactions:

N2 + 2O2→N2O4 ,ΔH=−8 kJ/mol

N2 + O2→2NO ,ΔH=180 kJ/mol

The equations given in the problem introduction can be added together to give the following reaction:

overall: N2O4→2NO + O2

However, one of them must be reversed, reaction 1: N2 + 2O2→N2O4

What is the enthalpy for reaction 1 reversed?

reaction 1 reversed: N2O4→N2 + 2O2

Express your answer numerically in kilojoules per mole.

What is the enthalpy for reaction 2?

Answer 1

Concepts and reason

The enthalpy change for a multiple step reaction can be calculated by using the concept of Hess’s law

Hess’s law states that in a multiple-step reaction, the overall enthalpy change is the sum of change in enthalpy in each step until the formation of the product.

Fundamentals

The example for overall enthalpy change calculation:

Given:

Overall equation:

The given equation is modified to derive the overall equation,

To get the overall equation, equation 1 is reversed. As equation 1 is reversed, the negative enthalpy becomes positive. Then, cancel the things that are similar or common in both reactions to get the final equation. The overall enthalpy is calculated by the sum of change in enthalpy in each step.

Overall enthalpy:

Equation 1 is reversed,

Ans:

Enthalpy for equation 1 is reversed:

The overall enthalpy of the reaction: