Unit 6

Heat

What is heat? heat – form of energy in moving particles of

matter

What is heat? at one time, people thought that heat was a

physical substance called “caloric”

What is heat? in 1798, American scientist, Benjamin

Thompson (Count Rumford) observed that mechanical energy could be converted to heat energy therefore, heat was not a physical substance but

rather a form of energy

What is heat? heat energy makes the particles of matter

move faster and further apart

heat is a form of energy because it can do work

adding or removing heat changes the temperature of a substance

Measuring Heat heat can be measured by observing the

temperature change it causes

when heat is added, the temperature of the substance rises

when heat is removed from the substance, its temperature falls

Calories calorie – unit of heat; amount of heat

needed to raise the temperature of 1 gram of water 1oC

a calorie is a very small amount of heat

Calories calories are used to measure the amount of

energy you get from food

a food calorie is 1000 times larger than the calorie used to measure heat

Calories food calories are written with a capital C

Calorie – 1000 calories, or 1 kilocalorie

Temperature heat is related to temperature

but they are not the same

Temperature heat is the energy of the moving particles of

matter

heat is kinetic energy

Temperature temperature – measure of the average

kinetic energy of the particles of the substance

Temperature as you remove heat from a substance, its

particles move slower absolute zero – lowest possible

temperature temperature at which particles of matter almost

stop moving

absolute zero is equal to -273OC

Temperature heat always moves from a place with a high

temperature to a place with a lower temperature

Freezing Point freezing point – temperature at which a

liquid changes to a solid

every liquid has its own freezing point

Freezing Point the freezing point of water is 0OC

when water freezes, it changes to ice

Melting Point melting point – temperature at which a solid

changes to a liquid

the freezing point and the melting point of a substance are the same

Boiling Point boiling point – temperature at which a liquid

changes to a gas

every liquid has its own boiling point

Boiling Point the boiling point of water is 100OC

when water boils, it turns to steam

Evaporation evaporation – change from a liquid to a gas

at the surface of the liquid

when a liquid stands uncovered at room temperature, it slowly changes to a gas

evaporation only happens at the surface of the liquid

Sublimation sublimation – change directly from a solid

to a gas

Conduction conduction – heat transfer in solids

heat travels by conduction when moving particles of matter bump into one another

Conduction conductors – substances that conduct heat

easily most metals are good conductors of heat

insulators – substances that do not conduct heat easily

Convection convection – heat transfer in gases and

liquids

Convection convection currents – up and down

movements of gases or liquids caused by heat transfer

heat is carried through air and water by means of convection currents

Convection many homes are heated by convection

forced air systems push heated air out of floor level vents to heat a room

hot water heaters pump heated water through radiators near the floor of a room

Radiation radiation – transfer of heat through space

space is a vacuum (empty space) so heat can not be transferred via conduction or convection

Radiation the earth receives heat from the sun via

radiation

Radiation some home heating systems use radiation

in a passive solar heating system, heat from the sun heats the house directly

in an active solar heating system, heat from the sun is collected by solar panels, this energy is used to heat water which is then pumped through the house like in a regular system

Thermal Expansion thermal expansion – expansion of a

substance caused by heating

Thermal Expansion most solids, liquids, & gases expand when

they are heated and contract when they are cooled

Thermal Expansion an exception to this rule is the freezing of

water

as water cools from 4OC to 0OC, it expands rather than contracts

this makes ice less dense than the surrounding water, causing the ice to float on the water