1. The problem statement, all variables and given/known data The overall activation energy E is 60 kcal/mol. Reaction steps are: CH3CHO --> .5CH3CO + .5CH3 + .5H2 E1 = 80 kcal/mol CH3CO --> CH3 + CO E2 = ? CH3 + CH3CHO --> CH4 + CH3CO E3 = 10 kcal/mol CH3 + CH3CO --> minor products E4 = 5 kcal/mol Estimate E2. 2. Relevant equations Arrhenius equation k = A exp (-E/RT) 3. The attempt at a solution Does E1 + E2 + E3 + E4 = E? If so, then E2 = -35 kcal/mol. If this is the case, what does negative activation energy mean (physically)? Do I need to use the Arrhenius equation and/or d[M]/dt expressions to solve this problem. Since E1 >> E3 and E4, are there any assumptions I can make? I feel like I'm missing something here. Thanks!