Answer:
5.21 kJ
Step-by-step explanation:
The transformation happens in steps. First, the liquid solution gains heat (Q1) and has its temperature elevated from 5.00°C to 47.6°C. Then, it vaporizes at a constant temperature, with the heat of vaporization (Q2). After that, the substance gains heat (Q3) and the temperature increases to 82.00°C.
The heat of the transformation with the change in temperature can be calculated by:
Q = m*c*ΔT, where m is the mass, c is the specific heat and ΔT the temperature variation.
The heat of the phase change is the heat of vaporization multiplied by the number of moles of the substance.
The total heat required is the sum of the heats of the steps. The molar mass of C2Cl3F3 is 187.4 g/mol. The number of moles is the mass divided by the molar mass:
n = 25/187.4 = 0.1334 mol
So,
Q1 = 25.0 g * 0.91 J/g.K * (47.6 - 5.00)K = 969.15 J
Q2 = 0.1334 mol * 27.49 kJ/mol = 3.6672 kJ = 3667.2 J
Q3 = 25.0 g * 0.67 J/g.K * (82.00 - 47.6)K = 576.2 J
Q = 969.15 + 3667.2 + 576.2
Q = 5212.55 J
Q = 5.21 kJ