Final answer:
To determine the energy change when 20.8 g of CH₃OH react with excess O₂, you would need the balanced chemical equation and the enthalpy change value for the reaction.
Step-by-step explanation:
The energy change when 20.8 g of CH₃OH react with excess O₂ can be determined by calculating the heat of reaction (ΔH). To calculate ΔH, you need to know the enthalpy change of the chemical reaction and the amount of substance involved. However, the given information does not provide the enthalpy change for the reaction.
To calculate the energy change, you would need the balanced chemical equation and the enthalpy change value for the reaction. Without these, it is not possible to determine the energy change accurately.