Ethanol (C2H5OH) melts a - 144 oC 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 heats of solid and liquid ethanol are 0.97j/g - k and 2.3 j/g - K, respectively.

(a) How much heat is required to convert 42.0 g of ethanol at 35 °C to the vapor phase at 78 °C?

(b) How much heat is required to convert the same amount of ethanol at - 155 oC to the vapor phase at 78 °C?

For a: The total heat required is 36621.5 J

For b: The total heat required is 58944.5 J

Explanation:

To calculate the heat required at different temperature, we use the equation:

        .........(1)

where,

q = heat absorbed

m = mass of substance

= specific heat capacity of substance

= change in temperature

To calculate the amount of heat required at same temperature, we use the equation:

     ........(2)

where,

q = heat absorbed

m = mass of substance

= enthalpy of the reaction

The processes involved in the given problem are:

We are given:

Change in temperature remains the same.

Putting values in equation 1, we get:

We are given:

Conversion factor: 1 kJ = 1000 J

Molar mass of ethanol = 46 g/mol

Putting values in equation 2, we get:

Total heat required =

Total heat required =

Hence, the total heat required is 36621.5 J

The processes involved in the given problem are:  

We are given:

Change in temperature remains the same.

Putting values in equation 1, we get:

We are given:

Putting values in equation 2, we get:

We are given:

Change in temperature remains the same.

Putting values in equation 1, we get:

We are given:

Putting values in equation 2, we get:

Total heat required =

Total heat required =

Hence, the total heat required is 58944.5 J

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