Answer:
-35,281.5 J
Explanation:
To convert the gaseous ethanol to liquid ethanol, three steps will occur. First, it will lose heat and the temperature will decrease until its boiling point, so from 300.0°C to 78.5°C. Thus, more heat will be lost, but now, with the temperature constant, so the gas will be converted to liquid. And then, the liquid will lose heat to decrease the temperature from 78.5°C to 25.0°C.
The total heat loss is the sum of the heats of each step. Because the heat is being removed from the system, it's negative. The first and last step occurs with a change in temperature, and so the heat is calculated by:
Q = m*c*ΔT
Where m is the mass, c is the specific heat of the gas (first step) or liquid (last step), and ΔT the temperature variation (final - initial). The mass of ethanol is the molar mass 46.07 g/mol multiplied by the number of moles, so:
m = 46.07 * 0.304 = 14.00 g
The second step occurs without a change in temperature, and the heat is then:
Q = -n*ΔH°vap
Where n is the number of moles, ΔH°vap is the heat of vaporization, and the minus signal indicates that the heat is being lost. Then, the heat of each step is:
Q1 = 14.00*1.43*(78.5 - 300,0) = -4434.43 J
Q2 = -0.304*40.5 = -12.312 kJ = -12312 J
Q3 = 14.00*2.45*(25.0 - 78.5) = -1835.05 J
Q = Q1 + Q2 + Q3
Q = -35,281.5 J
