Question

A 0.500-g sample of KCl is added to 50.0 g of water in a calorimeter (Figure 5.12). If the temperature decreases by 1.05°C, what is the approximate amount of heat involved in the dissolution of the KCl, assuming the heat capacity of the resulting solution is 4.18 J/g°C? Is the reaction exothermic or endothermic?

Short answer

The heat involved in the dissolution is 221.644 J and it is an endothermic reaction.

Step-by-step solution

Heat involved in the dissolution

Given information:

The mass of the sample = 0.500g

The mass of the water = 50.0g

Thus, the total mass of the calorimeter = 0.50 + 50 = 50.5g

The specific heat of the solution = 4.8 J/g°C

Rise or change in the temperature = 1.05°C

The heat evolved during the reaction is mathematically presented as \({\rm{Q = mC}}\Delta {\rm{T}}\). Therefore, by putting all the given values in \({\rm{Q = mC}}\Delta {\rm{T}}\), we get,

\({\rm{Q = 50}}{\rm{.5 }} \times {\rm{ 4}}{\rm{.18 }} \times {\rm{ 1}}{\rm{.05 = 221}}{\rm{.644 J}}\)

Endothermic reaction

In endothermic reactions, the heat is absorbed, which leads to a decrease in the temperature.Therefore, in the given reaction, the positive sign of heat signifies that the reaction is endothermic.