Answer: D. The temperature decreases after dissolution, and the process is endothermic.
Explanation:
Enthalpy is a thermodynamic variable defined as the <u>flow of thermal energy in chemical processes carried out at constant pressure when the only work is pressure-volume</u>, that is, the amount of energy that a system exchanges with its environment.
The enthalpy is related to the change of temperature in a process according to the following equation,
ΔH = - Cp ΔT = - Cp (T₂ - T₁)
where ΔH is the enthalpy change, Cp is the specific heat at constant pressure and ΔT is the variation of the temperature that happened in the process.
On the other hand, chemical reactions could be exothermic or endothermic:
- An exothermic reaction is any <u>chemical reaction that releases energy</u>, either as light or heat. In these reactions, a negative variation of the enthalpy ΔH < 0 occurs.
- An endothermic reaction is any chemical reaction that absorbs energy, usually in the form of heat, therefore ΔH > 0.
According to the explained, <u>if the enthalpy change in the dissolution process is positive</u>, as shown in the diagram (the final enthalpy is greater than the initial enthalpy and ΔH = H₂ - H₁ > 0), it means that <u>an energy absorption of the medium has occurred, so the temperature</u> (which is a physical quantity that reflects the internal energy and, therefore, the heat of a system) <u>has decreased</u>.
So, for the question in question, the temperature decreases after dissolution, and the process is endothermic.
