Thermal Energy

Thermal Energy

• Temperature & Heat

• Temperature is related to the average kinetic energy of the particles in a substance.

• SI unit for temp. is the Kelvin

• K = °C + 273 (10°C = 283K)

• °C = K – 273 (10K = -263°C)• Thermal Energy –

the total of all the kinetic and potential energy of all the particles in a substance.

• Thermal energy relationships

• As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).

• 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).

Heat

•The flow of thermal energy from one object to another.

• Heat always flows from warmer to cooler objects. Ice gets

warmer while hand gets

cooler

Cup gets cooler while hand gets

warmer

Types of Heat Transfer

3 WAYS THAT HEAT CAN TRAVEL SONG:

• https://www.youtube.com/watch?v=7Y3mfAGVn1c

Types of Heat TransferConduction

Conduction is the transfer of heat by direct contact. *occurs best in solids

Types of Heat TransferConvection

• Convection is the transfer of heat through fluids by currents created due to density differences in parts of the fluid. *occurs in liquids and gases only

Hot water rises, cools and falls. Heated air rises,

cools and then falls.Cool air falls.

Types of Heat TransferRadiation

• Radiation is the transfer of heat energy through space as waves of electromagnetic radiation. *the only type that can occur through empty space (example: from the sun)

Specific Heat

• Some things heat up or cool down faster than others.

Land heats up and cools down faster than water.

Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K).

C water = 4184 J / kg C

C sand = 664 J / kg C

This is why land heats up quickly during the day and

cools quickly at night and why water takes longer.

Specific Heat

• Which take longer to heat to 100°C?

C(cal/g°C)

C(J/g°C)

Water 1.00 4.18

Aluminum 0.22 0.90

Copper 0.093 0.39

Silver 0.057 0.24

Gold 0.031 0.1350g Al 50g Cu

Aluminum has a higher specific heat, so it will take longer to heat up. It will ALSO take longer to cool down.

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

q = mCpT

q = change in thermal energy (heat)

m = mass of substance

T = change in temperature (Tf – Ti)

Cp = specific heat of substance

-q means heat loss +q = heat gain

Heat TransferA 32g silver spoon cools from 60°C to

20°C. How much heat is lost by the spoon?

GIVEN

m = 32g

Ti = 60°C

Tf = 20°C

q = ??

C = 0.235 J/g°C

WORK

q = mCΔT

m = 32g

ΔT = Tf - Ti

ΔT = 20°C – 60°C = -40°C

q = (32g)(0.235J/g°C)(-40°C)

q = -300.8 J

Heat TransferHow much heat is required to warm 230 g of

water from 12°C to 90°C?GIVEN

m = 230g

Ti = 12°C

Tf = 90°C

Q = ??

C = 4.184 J/g°C

WORK

q = mCΔT

m = 230g

ΔT = Tf - Ti

ΔT = 90°C – 12°C = 78°C

q = (230g)(4.184J/g°C)(78°C)

q = 78,061 J

A piece of iron at a temperature of 145°C cools off to 45°C. If the iron has a mass of 10 g and a specific heat of 0.449 J/g°C, how much heat is given up?

GIVEN

m = 10g

Ti = 145°C

Tf = 45°C

q = ??

C = 0.449 J/g°C

WORK

q = mCΔT

m = 10g

ΔT = Tf - Ti

ΔT = 45°C – 145°C = -100°C

q = (10g)(0.449J/g°C)(-100°C)

q = -449 J

A calorimeter is used to help measure the specific heat of a substance.Heat gained = Heat lost

First, mass and temperature of

water are measured

Then heated sample is put

inside and heat flows into

water

T is measured for water to help get its heat gain

This gives the heat lost by

the substance

Knowing its q value, its mass, and its T, its Cp can be calculated

Let’s Practice!A 55.1 g piece of metal is heated to a temp of 45.1°C, and placed into a cup containing 359g of water at 20.0°C. The final temp of the water and metal is 22.3°C.•How much heat energy did the water absorb?

q = mcΔT

q = (359g)(4.18J/g°C)(22.3°C – 20.0°C) = 3.45 x 103J

•How much heat energy did the metal release to the water?

q lost = q gained

q lost by the metal = - 3.45 x 103J

The q is negative because heat was lost.

•What is the specific heat of the metal?

3.45 x 103J = (55.1g)(C)(22.3°C – 45.1°C)

2.75 J/g°C = C

Heat of Fusion

They Quantity of heat absorbed when a specific quantity of the solid is converted to liquid at its melting point is called its heat of fusion.

Heat of Vaporization

• The quantity of heat absorbed when a specific quantity of the liquid is converted to gas at the boiling point is called the heat of vaporization.

Phase Diagram

Fusion

VaporizationIce metls

Water boils

Liqu

id

Gas

Solid