Answer to Question #149868 in General Chemistry for Megan Wakley

Question

If a puddle of water at 0o​ ​C sits outside and freezes when 120 kJ of energy is removed (assume no temperature change) what mass of water freezes?

Answer 1

The heat Q required to change the phase of a sample of mass m is given by

Q = mL_f (melting/freezing)

Where m is the mass of the sample, and L_f is the Latent heat of fusion of the sample (334kJ/Kg for water).

Since this is phase change, the temperature remains constant.

Hence, substituting our values we get;

120kJ/Kg = (m)(334kJ/Kg)

$m=\dfrac{120kJ/Kg}{334kJ/Kg} = 0.359Kg$

= 35.9g