1. Write down a balanced molecular equation with physical states for the reaction of
a. Magnesium and hydrochloric acid;
b. Magnesium oxide and hydrochloric acid;
c. The formation of magnesium oxide from its elements, all in their standard states.
d. The formation of liquid water from its elements, all in their standard states.
2. Apply Hess’ law: combine the equations in #1 so that equation (c) is the sum of the other three
(a, b and d). You may need to reverse some of these equations and maybe multiply them by a
stoichiometric factor to get (c).
3. The enthalpy changes of the reactions in #1 are ΔHrxn(Mg+HCl), ΔHrxn(MgO+HCl), ΔHf°(MgO(s))
and ΔHf(H2O(l)), respectively. Looks at what you did in #2. Apply Hess’ law and write an algebraic
equation that shows how ΔHf°(MgO(s)) depends on the other three.