Classify each reaction as endothermic or exothermic.

h2 + br2 → 2hbr, δh = -73 kj
2nh3 → n2 + 3h2, δh = 92 kj
ch4 + 2o2 → co2 + 2h2o, δh = -890 kj
2hcl → h2 + cl2, δh = 184 kj

H2 + Br2 → 2HBr, ΔH = -73 kJ    Exothermic

2NH3 → N2 + 3H2, ΔH = 92 kJ     Endothermic

CH4 + 2O2 → CO2 + 2H2O, ΔH = -890 kJ     Exothermic

2HCl → H2 + Cl2, ΔH = 184 kJ         Endothermic

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%