Question

Calculate the heat required for the following two processes, and compare the results.


a. A 100.0 g sample of solid ethanol melts at its melting point. Hfus = 4.94 kJ/mol


b. A 100.0 g sample of liquid ethanol vaporizes at its boiling point. Hvap = 38.6 kJ/mol

Answer 1

Answer:

A. 10.74 KJ

B. 83.92 KJ

Explanation:

A. Data obtained from the question include the following:

Mass (m) of ethanol = 100g

Heat of fusion, Hfus = 4.94 kJ/mol

Heat (Q) =..?

Next, we shall determine the number of mole in 100g of ethanol, C2H5OH. This is illustrated below:

Mass of C2H5OH = 100g

Molar mass of C2H5OH = (2x12)+ (5x1) + 16 + 1 = 46g/mol

Number of mole (n) of C2H5OH =..?

Mole = Mass /Molar Mass

Number of mole (n) of C2H5OH = 100/46 = 2.174 moles.

Now, we can obtain the heat required to melt the ethanol as follow:

Q = n x Hfus

Q = 2.174 mol x 4.94 kJ/mol

Q = 10.74KJ

Therefore, 10.74 KJ of heat is required to melt the ethanol.

B. Data obtained from the question include the following:

Mass of C2H5OH = 100g

Heat of vaporisation, Hvap = 38.6 kJ/mol

Heat (Q) =..?

As calculated above, the number of mole in 100g of ethanol, C2H5OH is 2.174 moles.

The heat required to vaporise the ethanol can be obtained as follow:

Q = n x Hvap

Q = 2.174 mol x 38.6 kJ/mol

Q = 83.92 KJ

Therefore, 83.92 KJ of heat is required to vaporise the ethanol.

C. From the above calculations, a higher amount of heat energy i.e 83.92 KJ is required to vaporise the ethanol and a lesser amount of heat energy i.e 10.74 KJ is needed to melt the ethanol.

Answer 2

The heat required for the following two processes are:

a. 10.74 KJ

b. 83.92 KJ

Part a)

Given:

Mass (m) of ethanol = 100g

Heat of fusion, Hfus = 4.94 kJ/mol

To find:

Heat (Q) =?

Calculation for number of moles:

Mass of C₂H₅OH = 100g

Molar mass of C₂H₅OH = (2x12)+ (5x1) + 16 + 1 = 46g/mol

Number of Mole = Mass /Molar Mass

Number of mole (n) of C₂H₅OH = 100/46 = 2.174 moles.

Calculation for Heat of fusion:

Q = n x Hfus

Q = 2.174 mol x 4.94 kJ/mol

Q = 10.74KJ

Therefore, 10.74 KJ of heat is required to melt the ethanol.

Part b)

Given:

Mass of C₂H₅OH = 100g

Heat of vaporization, Hvap = 38.6 kJ/mol

To find:

Heat (Q) =?

Calculation for Heat of vaporization:

As calculated above, the number of mole in 100g of ethanol, C₂H₅OH is 2.174 moles.

The heat required to vaporize the ethanol can be obtained as follow:

Q = n x Hvap

Q = 2.174 mol x 38.6 kJ/mol

Q = 83.92 KJ

Therefore, 83.92 KJ of heat is required to vaporize the ethanol.

Find  more information about Heat of fusion here:

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