How many grams of magnesium must react to produce an enthalpy change of -58.5 kJ in the following reaction

2Mg(s)+O2(g) > 2MgO(s) delta H= -1203.6 kJ

Please explain steps to solve problem.

i know this is like arguing semantics but deltaH isn't + or -. it is just a change. the fact that you know that energy is released or absorbed is the key

2moles Mg yields 1203.6kJ
that's 601.8kJ/mole
58.5kJ / 601.8kJ/mole = 0.0972moles Mg
0.0972moles Mg x 24.3g/mole = 2.36g Mg