Answer :
Final answer:
To find the enthalpy change for a substance dissolving in a coffee-cup calorimeter, calculate the heat transfer from the temperature change and then divide by the number of moles of substance to get the enthalpy change per mole, assuming no heat is absorbed by the calorimeter.
Explanation:
The student is asking about the enthalpy change associated with a substance dissolving in water in a coffee-cup calorimeter. This is a thermodynamics problem in chemistry. The goal is to calculate the enthalpy change for the solution process in kilojoules per mole.
To find the enthalpy change, we need to know the amount of heat absorbed or released, the mass of the substance dissolved, and the molar mass of the substance. We assume that the calorimeter absorbs a negligible amount of heat and that the specific heat capacity of the solution is the same as that of water, which is 4.184 J/g°C.
Calculating the Heat Transfer (q)
First calculate the temperature change (ΔT) by subtracting the initial temperature from the final temperature.
Then, use q = m x c x ΔT to calculate the heat transfer, where m is the mass of water, c is the specific heat capacity of water, and ΔT is the temperature change.
Converting Heat Transfer to Enthalpy Change
Divide the heat transfer by the number of moles of the substance to find the enthalpy change per mole.
The number of moles is found by dividing the mass of the substance by its molar mass.
Since the temperature of the solution increases, this indicates that the dissolution process is exothermic, and the enthalpy change will be negative.