Energy Transfer

Aim: How does the air get heated?

Demo: Why are the beads moving in the beaker?

I. Incoming energy from the sun:

A. The sun shines upon the surfaces of Earth. B. Some energy gets reflected. C. Some energy gets absorbed by the

surfaces like water, soil, sand D. This transfer of energy from the sun to

ground is called radiation.

II. The Earth releases the energy as heat.

A. Molecules of air near the ground get heated by conduction (direct contact) Examples:

Hot pot handle Holding a spoon in flame

B. The heated air molecules: Move faster (gain more energy) Spread apart Become less dense and rise This is transfer of heat by movement of a

fluid (air or liquid) is called convection. Examples:

Radiator Boiling water in beaker Hot air above a fire

C. Convection current – Convection currents form when heated (less dense) air rises and forces cooler (more dense) air above to sink. This cycle repeats.

3 methods of energy transfer:

All 3 work together to heat the atmosphere

III. What happens to the air pressure as the warmed air

rises?

Warm, rising air molecules are less dense. Therefore, the air pressure also decreases.

Brainstorm:

Explain how methods of energy transfer are involved in heating a pot or beaker on the stove. How does the pot get heated? How does the soup get heated? How does the air above the pot get

heated?

Summary: Name the kind of energy transfer….

Sun shining on your face Heat felt from next to a campfire Toasting marshmallows over a campfire Sitting on top of the radiator The room warming from the heat of the

radiator Burning your hand on a light bulb in lab

class.

Specific Heat

The amount of energy needed to raise 1 gram of material by 1oC. Water has a high

specific heat (heats up slowly)

Sand has a low specific heat ( heats up quickly)

Ex.- Lead will heat faster, it requires less heat than copper

.13 J/goC .38J/goC

Adding the same energy to 2 different materials will raise the temperature different amounts because they have different specific heats.

Example:

What is the total # of Joules of heat energy gained by 3 grams of water when it is heated from 40oC to 60oC?

Energy = (mass)(change in temp)(specific heat)

Energy =(3 g)(20oC)(4.18J)Energy = 251

Phase changes require absorption of differing amounts of energy.

Phase changes

The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to liquid water or liquid water changing to ice

Phase changes of water

Heat of vaporization (Hv)

Describes the release or gain of energy during the evaporation condensation phase changes

Energy = (mass)(Hv)

Hv of water = 2260 J/g

Heat of fusion (Hf)

Describes the release or gain of energy during the melting freezingphase changes

Energy = (mass)(Hf)

Hf of water = 334 J/g

ESRT pg 1

Ex. 1-

Calculate the heat needed by 85 grams of solid ice to melt to a liquid at 0oC.

Ex. 2 -

Calculate the heat needed by 55 g of water to evaporate it all to water vapor at 100oC.

Summary:

Which phase change of water requires the MOST heat energy in order to occur?

Which phase change of water requires the LEAST heat energy in order to occur?