Calor-imetry(heat/energy) – (measuring)

• This is all about keeping track of where the energy goes!

• Physical changes are often accompanied by a transfer of energy.

• To understand that transfer of energy, you must consider both the substance in question and its surroundings.

Calorimetry

• Energy transfers that result in a temperature change for the substance and its surroundings.– Examples:• 1. external heat source• 2. substance loses heat to the surroundings• 3. substance gains heat from the surroundings• 4. whole system loses heat energy

Energy transfers that result in a temperature change for the substance and its surroundings

systemSurroundings

1

2

3

4

substance

Energy transfers that result in a temperature change for the

surroundings (but not the substance)

• Example:– Ice melting…• What has to happen to the ice for it to melt? • Where would that energy have come from? • Does the temperature of the ice change as it becomes

liquid water? • What about the temperature of the air around the ice

cube?

Calorimetry

• Energy changes in a laboratory setting are measured using a calorimeter.

• If heat is produced during the change, then the process/change/reaction is exothermic and the temperature of the surroundings will increase.

• Examples: 1. hand warmer 2. flame

Calorimetry

• If heat is consumed during the change, then the process/change/reaction is endothermic and the temperature of the surroundings will decrease.

• Examples: 1. cold pack 2. ice melting

Review!

1. The units in which heat energy is expressed are either or .

• 2. The quantity of heat energy required to raise the temperature of a unit mass of a substance by 1 C is called the of the substance.

3. The value of this quantity for water is .

4. In the calorimeter shown in the figure, a sample of solute releases 2.00 x 103 cal as it dissolves in water. Is this physical change endothermic or exothermic?

5. If the thermometer in the calorimeter shows a decrease in temperature over the course of an experiment, is the physical change in the chamber endothermic or exothermic?