Question

A 0.500-g sample of KCl is added to 50.0 g of water in a calorimeter. If the temperature decreases by 1.05 °C, what is the approximate amount of heat involved in the dissolution of the KCl, assuming the specific heat of the resulting solution is 4.18 J/g °C? Is the reaction exothermic or endothermic?

a) −209J, exothermic
b) 209J, endothermic
c) −209J, endothermic
d) 209J, exothermic

Answer 1

The heat involved in the dissolution of KCl is calculated using the formula q = mcΔT, yielding a value of approximately 219.45 J. The temperature decrease indicates an endothermic process, so the closest answer available is 209J, endothermic.

Step-by-step explanation:

To calculate the amount of heat involved in the dissolution of KCl, we use the formula: q = mcΔT, where m is the mass of the water, c is the specific heat of the solution, and ΔT is the change in temperature. For a 0.500-g sample of KCl added to 50.0 g of water, with a temperature decrease of 1.05 °C and a specific heat of 4.18 J/g °C, the calculation is as follows:

q = (50.0 g)(4.18 J/g °C)(-1.05 °C), q = -50.0 g × 4.18 J/g °C × -1.05 °C = 219.45 J, Since the temperature decreases, the reaction absorbs heat, indicating that it is an endothermic reaction. Therefore, the closest appropriate answer is (b) 209J, endothermic.