Please help with the following!!!! This Valentine\'s Day, you decide to win over
ID: 486944 • Letter: P
Question
Please help with the following!!!!
This Valentine's Day, you decide to win over that cute chemical engineer you've had your eye on by preparing chocolate fondue for them. This involves taking 100 g of solid chocolate, initially at 298 K, and melting it to obtain 100 g of liquid chocolate at 305 K. What is the enthalpy change associated with process? Assume that the solid chocolate has a heat capacity of 3.9 kJ/kg K at 298 K, its melting point is 305 K, and its heat of melting is 320 kJ/kg at 305 K. State any assumptions you make.Explanation / Answer
Preparing the chocolate involves two processes:
1) Heating the chocolate from 298 K to 305 K – let the enthalpy change for this process be Q1.
2) Melting the chocolate at 305 K – this is the melting point of the chocolate and the enthalpy associated is the enthalpy of fusion, Q2.
We have 100 g = (100 g)*(1 kg/1000 g) = 0.1 kg solid chocolate.
Q1 = (mass of solid chocolate)*(heat capacity of solid chocolate)*(change in temperature of solid chocolate) = (0.1 kg)*(3.9 kJ/kg.K)*(305 – 298) K = 2.73 kJ.
Q2 = (mass of chocolate)*(heating of melting) = (0.1 kg)*(320 kJ/kg) = 32 kJ.
The total heat involved in the process = Q1 + Q2 = (2.73 kJ) + (32 kJ) = 34.73 kJ (ans).
The assumption made is regarding the heat capacity of solid chocolate at 298 K. We have used the heat capacity in determining Q1 above. We must assume that the heat capacity is constant over the temperature range 298-305 K (ans).