Question

Propose a reaction mechanism for the following: Mg(s)+2HCl(aq)---->H2(aq)+MgCl2(aq)

The reaction order is 4; Rate=k〖[HCl]〗^2 〖[Mg]〗^2

I need help determining the elementary steps as chemical equations

Answer 1

1. Mg(s) --> Mg²⁺ + 2e^-

2. 2HCl(aq) --> 2H⁺(aq) + 2Cl^-(aq)

3. 2H⁺(aq) + 2e^-(aq) --> H₂ (g)

4. Mg²⁺(aq) + 2Cl^-(aq) --> MgCl₂ (aq)

Mg(s) + 2HCl(aq) ---> MgCl₂(aq) + H₂(g) -----------------------------(1)
Total ionic equation, by splitting all the (aq) molecules into their ions

Mg(s) + 2H⁺(aq) + 2Cl^-(aq) ------> Mg²⁺(aq) + 2Cl^-(aq) + H₂(g)

From (1) Rate = k [Mg] [HCl]²

The order of reaction should be 3 ( NOT 4 ), The reaction proceeds 1^st order kinetics with respect to Mg and 2^nd order kinetics with respect to HCl.