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.

  • 3
    $\begingroup$ 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. $\endgroup$
    – Buck Thorn
    Nov 2, 2023 at 16:27
  • $\begingroup$ Per mole of species in transition state. $\endgroup$
    – Mithoron
    Nov 2, 2023 at 17:10
  • $\begingroup$ To form 1 mole of TS? $\endgroup$
    – Shashaank
    Nov 2, 2023 at 17:27
  • $\begingroup$ @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? $\endgroup$
    – Shashaank
    Nov 2, 2023 at 17:33
  • 1
    $\begingroup$ 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). $\endgroup$
    – Karsten
    Nov 2, 2023 at 17:35


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