Thermal Energy

1. Temperature & Heat

Temperature is the measurement

of average kinetic energy of the

particles in a substance.

2. Units for temperature

a. SI standard is the Kelvin

b. Celsius is more common

3. Thermal Energy –

the total of all the

kinetic and potential

energy of all the

particles in a substance.

4. Thermal energy relationships

a. As temperature increases, so does

thermal energy (because the kinetic

energy of the particles increased).

b. Even if the temperature doesn’t

change, the thermal energy in a

more massive substance is higher

(because it is a total measure of

energy).

5. Heat

a. The flow of thermal

energy from one

object to another.

b. Heat alwaysflows from

warmer to

cooler objects. Ice gets warmer while hand gets

cooler

Cup gets cooler while hand gets warmer

6. Specific Heat

a. Some things heat up or cool

down faster than others.

Land heats up and cools down faster than water

b. Specific heat is the amount of heat

required to raise the temperature

of 1 kg of a material by 1o (C or K).

1) C water = 4184 J/kgoC

2) C sand = 664 J/kgoC

This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

Why does water have such a high specific heat?

Water molecules form strong bonds

with each other; therefore it takes

more heat energy to break them.

Metals have weak bonds and do not

need as much energy to break them.

water metal

How to calculate changes

in thermal energy

= change in thermal energy

= mass of substance

= change in temperature (Tf – Ti)

= specific heat of substance

Calculate the change in thermal energy of the water

in a pond with a mass of 1000 kg and a specific heat

of 4184 J/(kgoC) if the water cools by 1oC.

Calculate the specific heat of a metal if 0.5 kg of the

metal absorb 9000 J of heat as it warms by 10oC.

Find the change in thermal energy of a 20-kg wooden chair

that warms from 15º to 30º if the specific heat of wood

is 700 J/(kgº).

A concrete statue (specific heat = 600 J/kgoC) sits in

sunlight and warms up to 40oC. Overnight, it cools to 15oC

and loses 90 000 J of thermal energy. What is its mass?

c. A calorimeter is used to help measure

the specific heat of a substance.

First, mass and temperature of water are measured. The material is then heated, temp measured again. The sample is placed in the

water in the inner chamber, the sample cools as heat is transferred from the sample to the

water. When the temp of the sample & water are the same, a final temp is recorded.

Initial & Final Temp are known, the amount of heat gained can be calculated.