Post on 11-Dec-2015
• “How hot or cold something is”
• Measures avg. K.E. of the particles in the object.
• Tool: thermometer – meas. in degrees.
• Scales~ Celsius (°C) 0° - 100°~ Fahrenheit (°F) 32° - 212°~ Kelvin (K) 273 K – 373 K
0 K – Absolute zero
TemperatureTemperature
• Grand total KE & PE inside a substance.
• Depends on temp & amount of substance.
• Which beaker has more internal energy? Why?
Internal EnergyInternal Energy
• Amount of internal energy required to change temp.
• A substance does not contain heat – it contains internal energy.
HeatHeat
• Thermal Contact – objects in contact or mixed. Heat flows from higher temp. substance to low temp. substance.
• Thermal Equilibrium – thermal contacts reach same temp. – no heat flow.– Qlost = Qgained
– There is no net change in energy! Energy is conserved!
HeatHeat
• The internal energy changes when heat flows into or out of objects.
• Q = mc∆t– Q = heat transferred (calories or joules)
– m = mass (g)
– C = specific heat (cal/g-°C) or (J/g-°C)
– ∆t = change in temp. (°C)
Changes in HeatChanges in Heat
• Ability of a sub. to store internal energy.
• The amount of heat needed to raise the temp. of 1 g of the material 1 °C.
• Units: cal/g-°C.
Specific Heat of Materials
Substance Specific Heat (cal/g-°C)
Water 1.00
Wood .42
Aluminum .22
Glass .16
Iron .11
Copper .09
Silver .06
Specific Heat CapacitySpecific Heat Capacity
or
J/g-°C
• calorie - the amount of heat needed to raise the temperature of 1 g water 1 °C.
• Kilocalorie = Calorie (food unit).– 1 Kcal = 1000 calories
• Joule 4.186 J = 1 calorie.
Units of HeatUnits of Heat
How much energy would it take for 1 kg of aluminum to change from 22 °C to 32 °C?
Q = mc∆t
Q = 1000 g · .216 cal/g-C · 10 °C
Q = 2,160 calories
Calculate Heat TransferredCalculate Heat Transferred
Let’s compute how much energy it takes to make a cup of coffee or tea. Eight ounces of water has a mass of 0.22 kg. How much heat must be transferred to water to raise its temperature from 20 °C to 100 °C?
Q = mc∆t
Q = 220 g · 1 cal/g-C · 80 °C
Q = 17,600 calories
Calculate Heat TransferredCalculate Heat Transferred
A 50 g piece of metal immersed in boiling water is placed in 100 g of water at 20 °C. The final temperature of metal and water is 28 °C. What is the specific heat of the metal? What is the metal?
QL = QG
mc∆t = mc∆t
Methods of MixturesMethods of Mixtures
(50g)(c)(72 °C) = (100 g)(1.0cal/g ·°C)(8 °C)
c = .22 cal/g ·°C aluminum
A 50.0 g block of iron at 80 C is dropped into a cup of 200 g of water at 22 C. The block cools to 40 C. What would be the temperature change of the water?
QL = QG
mc∆t = mc∆t
Methods of MixturesMethods of Mixtures
(50 g)( .11 cal/g·°C)(40°C)=(200g)( 1cal/g°C)(∆T)
∆T = 1.1 °C 22 °C + 1.1 °C = 23.1 °C is Tf
Jerry grabs a hot 350.0 g brass spoon from his bowl of soup, originally at a temperature of 95.0 C. To avoid burning his fingers he drops the spoon into a sink of 1,250 g water at 18.0 C. One second later, the spoon has cooled to a temperature of 75.0 C. Calculate the temperature of the water at this time.
QL = QG
mc∆t = mc∆t
Methods of MixturesMethods of Mixtures
(350 g) ( .09 cal/g·°C) (20°C) = (1250g) ( 1cal/g°C) (∆T) ∆T = .504 °C
18 °C + .504 °C = 18.504 °C is Tf
Mechanical EnergyMechanical Energy
• Relates to motion
Potential Energy = mgd
Kinetic Energy = ½mv2
Work = F x d
W = PE = KE Unit: Joule (J)
Conservation of EnergyConservation of Energy
• Energy can’t be created or destroyed, but can change forms, including between thermal and mechanical.
Elost = Egain
Qlost = Qgain
KE = Qgain
PE = Qgain
W = Qgain
Mechanical Equivalent of Heat
Mechanical Equivalent of Heat
• Relationship of mechanical energy to thermal energy.
W = PE = KE = Q
1 calorie = 4.184 J
A 5 kg concrete block falls 10 m to the ground. If all of the block’s energy is converted into heat that is absorbed by the block only, it’s temperature is raised _____?
PE = Q
mgd = mc∆t
Mechanical – Thermal Energy
Mechanical – Thermal Energy
5 kg · 9.8 m/s2 · 10 m = 5 kg · 670 J/kg-°C · ∆t
∆t = 0.15 °C
• ↑heat energy - ↑kinetic energy - ↑motion.• Gas/Liquid/Solid
– ↑temperature – expand– ↓temperature – contract
Phase ExpansionPhase Expansion
• As the temp. decreases from 4°C to 0°C, water expands - ice.– Its density
decreases.
• The maximum density of water (1.0 g/mL) occurs at 4°C.
Thermal Exp. of WaterThermal Exp. of Water
• Thermometer
• Sidewalk joints
• Building materials
• Thermostat – bimetallic strip
• Consequences??
Uses of Thermal Exp.Uses of Thermal Exp.
• Different materials expand at different amounts with the same temperature rise.
• Thermal Coefficients for Length & Volume.
– Solids (length) L = LO x x T
Expansion RatesExpansion Rates
L = change in length L0 = original length
= coefficient of linear expansion
T = change in temperature
Linear Expansion Coefficients
Linear Expansion Coefficients
Material Coefficient ( C –1 )
Aluminum 23 x 10-6
Brass 19 x 10-6
Copper 16 x 10-6
Glass 3.2 x 10-6
Gold 14 x 10-6
Iron (Soft) 12 x 10-6
Lead 29 x 10-6
Quartz .40 x 10-6
Steel 11 x 10-6
Expansion RatesExpansion Rates
•The Eiffel Tower, constructed in 1889 by Alexandre Eiffel, is an impressive latticework structure made of steel. If the tower is 301 m high on a 22 oC day, how much does its height decrease when the temperature cools to 0.0 oC?L = LO x x T
= 301 m • 10.5 x10-6 • 22 °C
= .070 m