Ap Chem question

Question

How many kilojoules of heat are absorbed when 1.25 mol  is converted from liquid at 15.0℃ at vapor at 25.0℃? The specific heat of  (l) is 4.18 J/g℃. The heat of vaporization of water is 44.0 kJ/mol at 25℃.

Answer 1

1.25 moles of what? Water? Are you sure the problem asks about vaporization at 25ºC? Usually vaporization occurs at 100ºC. But if this is actually what is given to you, then...

q = mC∆T for heating the water from 15º to 25º and then q = m∆Hvap to convert it to vapor. Also, 1.25 moles H2O x 18 g/mole = 22.5 g.

To heat from 15 - 25 degrees: q = (22.5 g)(4.18 J/g/deg)(10 deg) = 941 J = 0.941 kJ

To vaporize the water at 25º: q = (1.25 moles)(44.0 kJ/mole) = 55 kJ

Total heat (in kJ) need = 55 kJ + 0.941 kJ = 55.9 kJ (to 3 sig. figs.)