What is the enthalpy change in the reaction, 2 CO + O2 2 CO2 called? a) Enthalpy of combustion b) Enthalpy of formation c) Enthalpy of fusion d) Enthalpy of reaction

The enthalpy change in the reaction $2\mathrm{CO}+\mathrm{O}{}_2\to 2\mathrm{CO}{}_2$ is called the enthalpy of combustion.

This is because combustion specifically refers to the reaction of a substance with oxygen, producing oxides and releasing heat. Here, carbon monoxide ($\mathrm{CO}$) is being oxidized to carbon dioxide ($\mathrm{CO}{}_2$), which is a classic example of a combustion reaction. The enthalpy change associated with such reactions is termed the enthalpy of combustion, representing the heat released when one mole of a substance burns completely in oxygen.

Carbon dioxideCarbon dioxide

The other options are incorrect:

• Enthalpy of formation refers to the formation of one mole of a compound from its constituent elements in their standard states.
• Enthalpy of fusion refers to the enthalpy change during phase transition from solid to liquid.
• Enthalpy of reaction is a general term for any enthalpy change in a reaction, but the specific term for combustion reactions is enthalpy of combustion.