The аctivаtiоn energy оf eаch step in a reactiоn was estimated using quantum mechanics: Step 1. Cl2 --> 2Cl Ea = 41 kJ/mol Step 2. H2S + Cl --> H2SCl Ea = 67 kJ/mol Step 3. H2SCl + Cl --> H2SCl2 Ea = 82 kJ/mol Step 4. H2SCl2 --> 2HCl + S Ea = 39 kJ/mol What is the slow step?