The combustion of hydrogen with oxygen is used to produce extremely high temperatures needed for certain types of welding procedures. What is the quantity of heat generated, in kj, when a 180g mixture containing equal parts oxygen and hydrogen gasses by masses burned? (ΔHrxn = -284 kj/mol)

This is a limiting reagent problem and combustion problem rolled into one. First determine the limiting reagent. I do them the long way.

2H2 + O2 --> 2H2O
mols H2 = 90/2 = 45 mols
mols O2 = 90/32 = about 3 but you need a better answer than that.
Convert mols H2 to mols H2O = about 45
Convert mols O2 to mols H2O = about 3*2 = about 6. The correct answer in limiting reagent problems is ALWAYS the smaller value; therefore, O2 is the limiting reagent and approx 3 mols will be used.
kJ released = 284 kJ/1 mol x approx 3 mol = approx ?