Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of...

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Enthalpy

Transcript of Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of...

Page 1: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

Enthalpy

Page 2: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

Specific Heat Capacity

• Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1oC.

• e.g. for water C= 4.18kJ kg-1 oC-1

• N.B. C changes for every liquid

Page 3: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

Measuring Heat Energy• Energy is measured in Joules (J):

1 kilojoule (kJ) = 1000 joules

• 4.18 kJ of energy is required to raise the temperature of 1kg of water by 1oC.

• To calculate the amount of heat energy needed to raise the temperature of a KNOWN VOLUME of water we use the equation:

Page 4: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

EH = c x m x ΔT

• EH = heat energy (kJ)• c = specific heat capacity of water• m = mass of water (kg)• ΔT = change in temperature (oC)

Page 5: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

ExampleQ. A kettle contains 500cm3 of water at a

temperature of 20oC.How much energy must be supplied to boil the water?

A. • EH = c x m x ΔT m=

500cm3=500g=0.5kg

= 4.18 x 0.5 x 80 ΔT= 100-20=

80oC = 167.2kJ

Page 6: Enthalpy. Specific Heat Capacity Definition: The HEAT ENERGY required to raise the TEMPERATURE of 1kg of substance by 1 o C. e.g. for water C= 4.18kJ.

ExampleQ. A Bunsen burning for 1 minute heated

100cm3 of water from 25oC to 75oC.Calculate the heat energy produced by the Bunsen.

• EH = c x m x ΔT m= 100cm3=100g=0.1kg

= 4.18 x 0.1 x 50 ΔT= 75-25=

50oC = 20.9kJ


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