Calorimetry

1

• Chapter 16
• Calorimetry

2
Calorimetry

• The study of heat flow and heat measurement.

3
Heat Capacity

• The amount of heat needed to raise the
  temperature of an object by 1 Celsius degree.

4
Specific Heat

• The heat capacity of 1 gram of a substance
• Specific Heat of liquid water is 4.184 J/gºC
• 4.184 J 1 calorie

5

• 1 Calorie 1000 calories 1 kilocalorie
• 1 Food Calorie 1000 calories

6
Calorimetry Experiments

• Determine the heats of reaction (ENTHALPY
  CHANGES) by making accurate measurements of
  temperature changes using a calorimeter.

7

• Scientists use q to denote measurements made in a
  calorimeter.
• Heat transferred in a reaction is EQUAL, but
  OPPOSITE in sign to heat absorbed by the
  surroundings.
• qrxn - qsur

8

• qsur m x Cp x (Tf Ti)

HEAT
Temperature change
Mass of Water
Specific heat of Water
9
KCl(s) ? K (aq) Cl- (aq)
First, calculate qsur and then calculate ?H.
10
KCl (s) ? K (aq) Cl-(aq)
qsur m x Cp x (Tf Ti)
qsur 75.0g x 4.184 J/gºC x (21.6 ºC 31.0 ºC
)
qsur -2949.72 J
11
qrxn - qsur 2949.72 J
qrxn represents the heat absorbed due to the
reaction of 12.8g KCl.
KCl (s) ? K (aq) Cl- (aq)
Now you must convert the KCl to moles.
12
1 mol KCl
12.8 g KCl

0.173 mol KCl
74 g KCl
13
KCl (s) ? K (aq) Cl- (aq)
2949.72 J

?H
x
1 mol KCl
0.173 mol KCl
Coefficient from balanced equation

17050 J
?H
?H Must be positive because it was an
endothermic reaction!

?H
17.1 kJ
14
qsur m x Cp x (Tf Ti)
207J 28.4g x Cp x 8.1oC
207J
Cp
0.90 J/g oC
28.4 g x 8.1 oC