150 g of liquid nitrogen at its boiling point of 77.0 K is stirred into a beaker containing 510 g of 18.0°C water.If the nitrogen leaves the solution as soon as it turns to gas,how much water freezes? The heat of vaporization of nitrogen is 48.0 cal/g and that of water is 80.0 cal/g.
A)none
B)21 g
C)42 g
D)11 g
E)63 g

Question

Quizplus · Accepted Answer

The heat absorbed by the nitrogen as it turns to gas is:$$Q_1=150	ext{ g}	imes48	ext{ cal/g}=7200	ext{ cal}$$The heat released by the water as it freezes is:$$Q_2=m	imes80	ext{ cal/g}$$where m is the mass of water that freezes.Equating Q1 and Q2, we get:$$7200	ext{ cal}=m	imes80	ext{ cal/g}$$$$m=\frac{7200	ext{ cal}}{80	ext{ cal/g}}=90	ext{ g}$$Therefore, 90 g of water freezes.

150 G of Liquid Nitrogen at Its Boiling Point of 77.0