A student conducts an experiment in which they dissolve 1 g each of several substances in 50 mL of water. They have 12 identical plastic cups of water and place 1 g of salt into three of the cups, 1 g of sugar into three of the cups, and 1 g of baking soda into three of the cups. The three remaining cups contain only water. All the cups are put in a freezer, and the temperature of the solution in each cup is recorded every 15 minutes for 4 hours. Which of the following questions is the student most likely investigating?