Draw a phase diagram for this question: Ethanol (C 2 H 5 OH) melts at -114 °C an

Question

Draw a phase diagram for this question:

Ethanol (C2H5OH) melts at -114 °C and boils at 78 °C. Its density is 0.789 g/mL. The enthalpy of fusion of ethanol is 5.02 kJ/mol, and its enthalpy of vaporization is 38.56 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-°C and 2.3 J/g-°C, respectively. How much heat (in kJ) is required to convert 25.0 g of ethanol at 25 °C to the vapor phase at 78 . How much heat is required to convert 5.00 L of ethanol at -140 °C to the vapor phase at 78 °C ?

Explanation / Answer

1) Molar mass of ethanol = 46 g/mole

Thus, moles of 25 g of ethanol = mass/molar mass = 25/46 = 0.543

Heat required = mass of ethanol*specific heat capacity*change in temperature + moles of ethanol*heat of vaporisation

or, Heat required = 25*2.3*(78-25) + 0.543*38560 = 3047.5 + 20938 = 23985.58 J = 23.986 kJ

2) mass of ethanol = volume*density = 5000*0.789 = 3945 g

moles of ethanol = mass/molar mass = 85.761

Now, heat required = mass of ethanol*specific heat*change in temperature + moles of ethanol*heat of fusion + mass of ethanol*specific heat*change in temperature + moles of ethanol*enthalpy of vaporisation

or, heat required = (3945*0.97*26) + (85.761*5020) + (3945*2.3*192) + (85.761*38560) = 99492.9 + 430520.22 + 1742112 + 3306944.16 = 5579069 J = 5579.069 kJ

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