When placed in acid, magnesium metal reacts and forms hydrogen gas:

Mg(s) + HCl(aq) --> MgCl2(aq) + H2(g) ΔH = -56.5 kJ/mol

If HP denotes the enthalpy of products and Hr denotes the enthalpy of reactants, then:

Hp > Hr
Hp < Hr
Hp = Hr

I put Hp > Hr because of ΔH = -56.5 kJ/mol, am I correct?

If Hp > Hr wouldn't you end up with a + number