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
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