A researcher wishes to predict how much the temperature of water will rise when a particular mass of anhydrous CaCl2 is quickly dissolved. In a preliminary experiment, 2.50 g of CaCl2 (molar mass = 111.0 g mol−1) is added to 150.0 g of water at 23.0 °C in a well-insulated cup that has negligible heat capacity. After complete dissolution, the solution reaches 28.1 °C. Assume the specific heat capacity of the solution remains the same as that of pure water throughout.
Using only the information from the preliminary experiment and neglecting any heat capacity of the cup, answer the following.
(a) Calculate the energy change associated with dissolving 2.50 g of CaCl2 in the preliminary experiment. Include the sign.
(b) Determine the energy change per gram of CaCl2 dissolved.
(c) Using this relationship, predict the final temperature if 7.50 g of CaCl2 were dissolved in the same mass of water under identical conditions. Show all steps in your reasoning.
(d) State one assumption inherent in your prediction that, if violated, could lead to a significant discrepancy between the predicted and actual final temperature, and explain the effect qualitatively.