Heat, q , is energy transferred between a system and its surroundings. For a pro
ID: 839322 • Letter: H
Question
Heat, q, is energy transferred between a system and its surroundings. For a process that involves a temperature change
q=m?Cs??T
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=n??H
where, n is the number of moles and ?H is the enthalpy of fusion, vaporization, or sublimation.
The following table provides the specific heat and enthalpy changes for water and ice.
Calculate the enthalpy change, Delta H, for the process in which 38.7g of water is converted from liquid at 12.4 Degrees C to vapor at 25.0 Degrees C . For water, Delta Hvap = 44.0kJ/mol at 25.0 Degrees C and Cs = 4.18 J/(Degrees C) for H2O(l).
Substance Specific heat[J/(g??C)] ?H
(kJ/mol) water 4.18 44.0 ice 2.01 6.01
Explanation / Answer
enthalphy change = Q(due to change in temperature) + Q( due to change in state)
= 38.7*4.18*(25 - 12.4) + 38.7*44000/18
= 2038.2516 + 94600
= 96.64 kilo joules
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