Heat: Lesson 4

Heat vs. Temperature

What happens to the movement of molecules as they’re heated?

• http://phet.colorado.edu/en/simulation/energy-forms-and-changes

What is temperature?

• Temperature is the average kinetic energy of matter. The more the molecules move the higher the temperature will be.

=

Thermal Energy

• Thermal energy is the total amount of energy in a sample. It involves the temperature and amount of a substance.

+

Which sample has more thermal energy?

50 mL at 100 °C 100 mL 100 °C

Sample A Sample B

=thermal energy

Which one has more thermal energy: A or B?

50 mL at 80 ° C 10 mL at 100 ° C

100 mL temp increases from 22 °C to 38 ° C 100 mL temp increases from 22 °C to 29 ° C

A B

Law of Conservation of Energy

System Surroundings

• The amount of energy released or absorbed by a process can be quantified by the following equation:

q = m x x ΔT• q = • m = • ΔT = • 1 calorie is the amount of energy that it takes

to raise 1 gram of water 1°C .

PRACTICE:A 100 gram sample of water is at 50°C . The water sample cools to 25°C. How many calories did the sample lose to the surroundings?

q = m x x ΔT

q =

m =

ΔT = (Tfinal– Tinitial)

= (___ – ___)

= ( _____ )

PLUG IN AND SOLVE:

PRACTICE:200 mL of 50°C water is mixed with 75 mL of 90°C water. The final temperature of the water is 60.9°C. How much heat did the 50 °C water gain?

q = ______

m = ______

ΔT = (Tfinal– Tinitial)

= (___ – ___)

= ( _____ )

q = m x x ΔT

PLUG IN AND SOLVE:

PRACTICE: 200 mL of 50°C water is mixed with 75 mL of 90°C water. The final temperature of the water is 60.9°C. How much heat did the 90°C water lose?

q = ______

m = ______

ΔT = (Tfinal– Tinitial) = (___ – ___)

= ( _____ )

q = m x x ΔT

PLUG IN AND SOLVE:

This example proves the _________________________because the energy ________ by the _______ water, 2180 calories, is equal to the energy _______ by the _______ water, 2180 calories.

Hot Water Cold Water