Heat, q, is energy transferred between a system and its surroundings. For a process that involves a temperature change
q=mâ Csâ ÎT
where Cs is specific heat and m is mass.
Heat can also be transferred at a constant temperature when there is a change in state. For a process that involves a phase change
q=nâ ÎH
where, n is the number of moles and ÎH is the enthalpy of fusion, vaporization, or sublimation.
The following table provides the specific heat and enthalpy changes for water and ice.
Substance Specific heat
[J/(gâ âC)] ÎH
(kJ/mol) water 4.18 44.0 ice 2.01 6.01
Part A
Calculate the enthalpy change, ÎH, for the process in which 45.7 g of water is converted from liquid at 10.1 âC to vapor at 25.0 âC .
For water, ÎHvap = 44.0 kJ/mol at 25.0 âC and Cs = 4.18 J/(gâ âC) for H2O(l).
Part B
How many grams of ice at -12.5 âC can be completely converted to liquid at 8.1 âC if the available heat for this process is 5.27Ã103 kJ ?
For ice, use a specific heat of 2.01 J/(gâ âC) and ÎHfus=6.01kJ/mol.
Express your answer to three significant figures and include the appropriate units.
Heat, q, is energy transferred between a system and its surroundings. For a process that involves a temperature change
q=mâ Csâ ÎT
where Cs is specific heat and m is mass.
Heat can also be transferred at a constant temperature when there is a change in state. For a process that involves a phase change
q=nâ ÎH
where, n is the number of moles and ÎH is the enthalpy of fusion, vaporization, or sublimation.
The following table provides the specific heat and enthalpy changes for water and ice.
| Substance | Specific heat [J/(gâ âC)] | ÎH (kJ/mol) |
| water | 4.18 | 44.0 |
| ice | 2.01 | 6.01 |
Part A
Calculate the enthalpy change, ÎH, for the process in which 45.7 g of water is converted from liquid at 10.1 âC to vapor at 25.0 âC .
For water, ÎHvap = 44.0 kJ/mol at 25.0 âC and Cs = 4.18 J/(gâ âC) for H2O(l).
Part B
How many grams of ice at -12.5 âC can be completely converted to liquid at 8.1 âC if the available heat for this process is 5.27Ã103 kJ ?
For ice, use a specific heat of 2.01 J/(gâ âC) and ÎHfus=6.01kJ/mol.
Express your answer to three significant figures and include the appropriate units.
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