Answer:
-16,873.25 J
Step-by-step explanation:
This process will occur in steps. First, the temperature will decrease until the boiling point, then the ethanol will suffer a phase change from gas to liquid, and then, the temperature will decrease to 25.0°C. Because the temperature is decreasing, it is losing heat, and so, for all process the heat is negative, also H°vap is negative.
For the first and last step, the heat occur with a temperature change, and it can be calculated by:
Q = m*c*ΔT
Where m is the mass, c is the specif heat, and ΔT is the temperature variation. The mass is the number of moles multiplied by the molar mass (46.07 g/mol for ethanol), so m = 0.310*46.07 = 14.28 g.
For the second step, the heat lost is:
Q = - n*H°vap
At first step the substance is a gas, so c = cgas, and at the third step, the substance is a liquid, and c =cliquid.
Q1 = 14.28*1.43*(78.5 - 201) = -2501.5 J
Q2 = -0.310*40.5 = -12.5 kJ = -12500 J
Q3 = 14.28*2.45*(25.0 - 78.5) = -1871.75 J
Q = Q1 + Q2 + Q3
Q = -16873.25 J