Ethanol (C2H5OH ) melts at -114 C and boils at 78 C . The enthalpy of fusion of

Question

Ethanol (C2H5OH ) melts at -114 C and boils at 78 C . The enthalpy of fusion of ethanol is 5.02 kJ/mol , and its enthalpy of vaporization is 38.56 kJ/mol . The specific heat of solid and liquid ethanol are 0.97 J/gK are 2.3 J/gK respectively.

A.) How much heat is required to convert 34.5 g of ethanol at 38 C to the vapor phase at 78 C ? Express your answer using two significant figures.

B.) How much heat is required to convert 34.5 g of ethanol at -169 C to the vapor phase at 78 C ? Express your answer using two significant figures.

Explanation / Answer

Q = m c T
Q = quantity of heat in joules (J)
m = mass of the substance acting as the environment in
grams (g)
c = specific heat capacity (4.19 for H2O) in J/(g oC)
T = change in temperature = Tfinal - Tinitial in oC

Let us do the same calcualtion for vapour phase also using the same equation

Question A

Q = 34.5 x 2.3 x (78-38) + 34.5 x 38.56 x 103 / 46.07

Q = 3174 + 28876.06 = 32050.06 Joules

32050.06 Joules of heat is required to convert 34.5 g of ethanol at 38 C to the vapor phase at 78 C

Question B

Q = 34.5 x 0.97 x (169-114) + 34.5 x 5.02 x 103 / 46.07 +  34.5 x 2.3 x (92) + 34.5 x 38.56 x 103 / 46.07

Q = 1840.575 + 3759.28 + 7330.2 + 28876.06 = 41776.114 Joules

41776.114 Joules of heat is required to convert 34.5 g of ethanol at -169 C to the vapor phase at 78 C

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