heat

Heat• Objectives

– Be able to distinguish between heat and temperature

– Be able to explain thermal equilibrium

– Identify the three ways heat can be transferred

– Understand specific heat and latent heat

What is Temperature?

Temperature is our measurement of the average kinetic energy found in the random motions and vibrations of countless atoms and molecules.

Temperature is a way of quantifying the kineticenergy of these atoms and molecules.

Temperature is Energy.

Maxwell-Boltzman Velocity Distribution

Higher temperatures

mean higher

velocities for

atoms and

molecules

Heat TransferThree Modes of Heat Transfer

Radiation

Convection

Conduction

RadiationEnergy transport via electromagnetic waves

ConvectionEnergy transport by mass motion

ConductionEnergy transport by vibrational translation

The jostling of atoms andmolecules in close proximityin a solid, especially one withhigh conductivity.

Specific Heat• Q = m c T Q = HEAT ENERGY

m = mass

T = Temperature difference

c = specific heat responsible for the thermal

properties of the substance

(Joules/kg/Celsius)

T = Q/mc

Specific Heat T = Q/mc

For a given amount of heat energy, say 10,000 Joules,

what is the temperature change for 1 kg of water and

1 kg of sand?

Csand = 838 J/kgoC

Cwater = 4186 J/kgoC

Tsand = 10,000/1(838) = 11.9 oC

Twater = 10,000/1(4186) = 2.4 oC

Heat Energy

Changes of StateEnergy Increased and Absorbed by Substance:

• SOLID to LIQUID Melting

• LIQUID to GAS Boiling

• SOLID to GAS Sublimation

Energy Decreased and Released by Substance:

• GAS to SOLID Deposition

• GAS to LIQUID Condensation

• LIQUID to SOLID Freezing

Latent Heat

Latent Heat of Fusion

Heat Energy required to convert solid to liquid Lf

Latent Heat of Vaporization

Heat Energy required toconvert liquid to gas.Lv

Melting T = Q/mc

Amount of heat energy needed to bring a 25 g ice

block to a temperature of 50oC?

Starting Temp = 0oC

Ending Temp = 50oC

Q = heat needed to make transition from ice to water

+ heat needed to heat water from 0 to 50 oC

Q = mLf + mcT

Melting Ice Q = m Lf + m c T

Q = heat needed to make transition from ice to water

+ heat needed to heat water from 0 to 50 oC

= 80 cal/g*(25 g)*(4.186 J/1000 Cal)

+ 25 g *4.186 J/goC *(50-0 oC)

= 8.37 J + 5230 J

= 5238.4 J

Temperature ConversionsCELCIUS

C = 5/9 (F-32)

FAHRENHEIT

F = (9/5 C) + 32

ABSOLUTE or KELVIN

K = C + 273