Heat of Vaporization and Heat of Fusion Learning Goal: To calculate the total energy required to convert...

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Chemistry

Heat of Vaporization and Heat of Fusion

Learning Goal:

To calculate the total energy required to convert a solid to agas using heat capacity, heat of fusion, and heat ofvaporization.

The amount of heat required to melt one mole of a solid is calledthe heat of fusion (ΔHfus). The amount of heatrequired to vaporize (boil) one mole of a liquid is called theheat of vaporization (ΔHvap). The heat of fusionand the heat of vaporization can be used to calculate the amount ofheat needed to melt or vaporize, respectively, a given amount ofsubstance.

For example, the heat of fusion for H2O is 6.02 kJ/mol, whichmeans that 6.02 kJ of heat is needed to melt a mole of ice. Twiceas much heat is needed to melt twice as much ice, as shownhere:

2.00 mol×6.02 kJ/mol=12.0 kJ

Constants

Heat of fusion (ΔHfus) is used for calculationsinvolving a phase change between solid and liquid, with notemperature change. For H2O, ΔHfus=6.02 kJ/mol.

Specific heat capacity (C) is used for calculationsthat involve a temperature change, but no phase change. For liquidwater, C=4.184 J/(g⋅∘C).

Heat of vaporization (ΔHvap) is used for calculationsinvolving a phase change between liquid and gas, with notemperature change. For H2O, ΔHvap=40.7 kJ/mol.

Part A

How much heat is required to melt 52.5 g of ice at its meltingpoint?

Express your answer numerically in kilojoules.

17.5

  kJ  

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Correct

Part B

How much heat is required to raise the temperature of52.5 g of water from its melting point to its boilingpoint?

Express your answer numerically inkilojoules.

158.0775

  kJ  

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****NEED HELP PLEASE PART B ANSWER IS WRONG****

Answer & Explanation Solved by verified expert
3.7 Ratings (327 Votes)

q = m c dT       -- equation 1   

Where, q = heat change                                                 , m= mass in gram,

c = specific heat (in terms of J/gK)                     

dT = final temperature – initial temperature.

Part B. Given,

                Mass of water = 52.5 g

                Initial temperature of water = 00C             [Melting point]

                Final temperature of water = 1000C          [Boiling point]

                dT = 1000C – 00C = 1000C

                Specific heat = 4.184 J/g0C

Putting the values in equation 1

                q = 52.5 g x (4.184 J/g0C) x 1000C

                or, q = 21966 J   = 21.966 kJ                                          ; [1 kJ = 1000 J]

Therefore, the amount of heat required to raise the temperature = 21.966 kJ


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