Question

Consider the following thermochemical equation:

C(s) + O₂(g) → CO₂(g) δh = −393 KJ

CO(g) + ½O₂(g) → CO₂(g) δh = −294 KJ


What is the enthalpy change for the following related thermochemical equation?

Answer 1

The enthalpy change for the conversion of CO(g) to C(s) and ½O₂(g) is +110.5 kJ, calculated by reversing the combustion of carbon to CO₂(g) and combining it with the formation of CO₂(g) from CO(g) using Hess's law.

Step-by-step explanation:

To calculate the enthalpy change for the reaction CO(g) + ½O₂(g) → CO₂(g), we can use Hess's law and the given thermochemical equations. We need to manipulate the provided reactions to find a pathway that leads to the desired reaction.

First, we reverse the combustion of carbon to form CO₂(g):

• C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ becomes CO₂(g) → C(s) + O₂(g) ΔH = +393.5 kJ

Now let's examine the formation of CO₂(g) from CO(g):

• CO(g) + ½O₂(g) → CO₂(g) ΔH = -283.0 kJ (this is the desired reaction with its ΔH)

Adding these two equations:

• CO(g) + ½O₂(g) → CO₂(g) ΔH = -283.0 kJ
• CO₂(g) → C(s) + O₂(g) ΔH = +393.5 kJ

Cancel out the CO₂(g) on both sides to get the net reaction:

• CO(g) → C(s) + ½O₂(g) ΔH = +110.5 kJ (since -283.0 kJ + (+393.5 kJ) = +110.5 kJ)

This indicates that the enthalpy change for the conversion of CO(g) to C(s) + ½O₂(g) is +110.5 kJ.