# Units of Activation Energy

Consider the reaction $$\ce{aA + bB -> cC + dD}$$ whose reactants are given by A and B and the products are C and D.

Say the activation energy of this reaction is some $$x$$ joules/mole, But moles of what ( $$A$$ or $$B$$ or $$C$$ or $$D$$) ?

If I need $$x$$ joules of energy to react $$A$$ with $$B$$ with the correct orientation, To react $$a$$ moles of $$A$$, I would need $$ax$$ Joules of energy, if it was $$x$$ joules of energy to react $$B$$ with $$A$$, I would need $$bx$$ amount of energy to react $$b$$ moles of $$B$$. Since the reaction is the same the amount of energy needed should be constant to react a fixed concentration of reactants. I know I am missing some understanding here.

• Think of it as "moles of reaction". If there are x moles of reaction, then xa moles of A react with xb moles of B. Nov 2, 2023 at 16:27
• Per mole of species in transition state. Nov 2, 2023 at 17:10
• To form 1 mole of TS? Nov 2, 2023 at 17:27
• @BuckThorn So to form c moles of C and d moles of D from a moles of A and b moles of B, I need x joules of energy? Nov 2, 2023 at 17:33
• If it is activation energy, you need that amount but will get some back. In general, molar quantities are per mole of reaction (enthalpy of reaction, Gibbs energy of reaction).
– Karsten
Nov 2, 2023 at 17:35