Calorimetry

1
Calorimetry
General Chemistry 101/102Laboratory
ManualUniversity of North Carolina at Wilmington
2
Calorimetry

• Purpose

• To learn techniques for measuring changes in
  thermal energy (heat) in substances.
• To examine the relationship between the specific
  heat capacity of a metal and its atomic weight.

3
Calorimetry

• Background

• The thermal energy (q) transferred when an object
  is heated or cooled can be calculated from the
  following equation

4
Calorimetry

• Background

• When two objects such as hot metal and cold water
  are brought into contact, the heat lost by the
  hotter object is equal to the heat gained by the
  cooler object.

(2) qwater - qmetal
The minus sign is necessary since heat loss is an
exothermic process (q is negative) while heat
gain is an endothermic process (q is positive).
5
Calorimetry

• Background

• Substituting Eqn (1) into Eqn (2) leads to an
  equation that allows us to calculate the specific
  heat capacity of a metal by making a few simple
  temperature measurements.

(3) swater x gwater x DTwater - smetal
x gmetal x DTmetal
6
Calorimetry

• Procedure

• Determine the mass of your assigned metal by
  emptying the metal onto a paper towel and
  weighing the empty test tube with its stopper.
  Return the metal to the test tube and weigh the
  test tube with its stopper again.
• Place the test tube in a beaker of boiling water
  for 10 minutes. Be careful not to allow any
  water to splash inside the test tube. The metal
  must remain dry.

7
Calorimetry

• Procedure

• While the metal is heating, weigh two nested
  styrofoam cups (coffee cup calorimeter).
• Add about 40 mL of water to the inner cup and
  weigh the setup again. Determine the mass of
  water in the calorimeter.
• Measure and record the temperature of the water
  in the calorimeter.

8
Calorimetry

• Procedure

• Remove the test tube from the boiling water and
  quickly empty the contents into the calorimeter.

• Stir the contents of the calorimeter and record
  the highest temperature reached. Be sure the
  temperature probe is not touching the metal when
  you make your temperature measurements.

9
power connector and serial/USB connector
USB connector on computer
temperature probe connected to the Microlab unit
10
2
1
graph area
3
data table
live data