The relationship you need is q = nΔHvap where q is heat (in kJ), n is number of moles of substance (water), and ΔHvap is the heat of vaporization of the substance (for water, from reference information in text or online)
You are asked for: q = ?
You are given: mass = 2.5 kg
You look up: ΔHvap for water: 40.67 kJ/mol
Convert mass of water from kg to g, and then to mol (using the molar mass for water: 1 mol = 18.02 g):
2.5 kg x 1000 g/1 kg = 2500 g
2500 g H2O x 1 mol H2O /18.02 g H2O = 139 mol H2O
n = 139 mol H2O
Substitute values in equation:
q = (139 mol H2O)(40.67 kJ/mol) = 5642 kJ
the heat required to evaporate 2.5 kg water is 5642 kJ
Jenna R.
It was all good until the substitute values in equation if you leave what you got for the answer in moles in the calculator and times it by KJ/mol then you will get 138.7347392mol x (44.01KJ/1mol) = 6105.71 KJ round it to two sig figs and get 6100.02/23/21