At the boiling point of nitrogen, N2 , how many joules are needed to vaporize 14.6 g of N2 ? Liquid nitrogen has a heat of vaporization of 198 J/g at its boiling point

Answer 1

At the boiling point, in order to vaporize the liquid, all the heat goes into vaporization and there is no change in the temperature. This is simply a phase change.

q = m∆Hvap

q = heat

m = mass

∆Hvap = heat of vaporization

q = (14.6 g)(198 J / g) = 2891 J = 2890 J (3 sig. figs.)