Final answer:
The enthalpy change for the reaction is the essential information needed to calculate the heat absorbed when preparing NO₂ from N₂ and O₂, reflecting the endothermic nature of the reaction.
Step-by-step explanation:
To determine the heat absorbed in the endothermic reaction of preparing NO₂ from N₂ and O₂, the crucial piece of information needed is the enthalpy change for the reaction. This value provides a direct measure of the heat that is absorbed or released when the reaction occurs under standard conditions. Since the reaction is endothermic, this value will be positive, reflecting the fact that heat is consumed to drive the reaction forward.
Specific heat is relevant when calculating the heat absorbed by a substance as its temperature changes; however, it is not directly necessary for calculating the total heat absorbed in a chemical reaction. Activation energy is a concept used to understand the energy barrier that reactants must overcome to form products and while it does relate to the temperature dependence of the rate at which the reaction occurs not used to calculate the heat absorbed.