Thermal Expansion. the expansion or contraction of objects due to heat in or out Generally speaking : Heat in > expansion! Heat out > contraction!. Thermal Expansion. Thermal Energy the total PE and KE that is associated with the molecules of a substance .
the expansion or contraction of objects due to heat in or out
Heat in > expansion!
Heat out > contraction!
Thermal Energy the total PE and KE that is associated with the molecules of a substance
Heat the transfer of thermal energy-- thermal energy goes out of one body and into some other
Temperature What the hell does it measure?
Absolute zero (0˚K)-- the temperature at which molecular motion (and KE) will be the least.
˚K = ˚C + 273
‡a calorie was originally defined as the amount of heat needed to raise 1 g of H2O up 1 ˚C
4.19 J = 1 cal
How much a substance will expand or contract depends upon 3 things:
type of material
Because God is not a DUMBASS!
if HE were like you:
because he is NOT:
the coefficient of linear expansion ()
area expansion = 2
If we are concerned about the volume that a solid is expanding:
volume expansion = 3
An aluminum rod is initially 5.000 m long at 20.0 ˚C. How long will the rod be when heated to a temperature of 100.0 ˚C?
= 25 X 10-6 /˚C
∆l = • l∆T
l = 5.000 m
=(25 X 10-6/˚C)(5.000 m)(80.0˚C)
Ti = 20.0˚C
= .0100 m
l = ?
Tf = 100.0˚C
l = l + ∆l = 5.000 m + .0100 m
= 5.010 m
the coefficient of volume expansion ()
2.000 L of a liquid will expand to a volume of 2.119 L when heated from 25.0 ˚C to 65.0˚C. What must this liquid be?
V = 2.000 L
V = 2.119 L
Ti = 25.0 ˚C
= .119 L
Tf = 65.0 ˚C
1.49 X 10-3 /˚C
∆V = .119 L
=1490 X 10-6/˚C
∆T = 40.0 ˚C
A steel rivet that is 1.871 cm in diameter at 20.0˚C needs to be cooled to what temperature so that it will fit in the rivet hole which is 1.869 cm?
A steel rod and a brass rod are each exactly 25.000 cm long at 20.0˚C. Both are then heated to 100.0˚C. Which rod is longer and how much longer is it?
How much gas will spill out of a 12.00 L tank if it is filled to capacity at 0.0˚C and heated to 75.0˚C? Assume the tank is made out of some magic stuff that won’t expand at all. Happens everyday.
A glass (α = 9 X 10-6/˚C) beaker that is 1000.0 cm3 is filled to the brim with ethyl alcohol (β = 1100 X 10-6/˚C) at 20.0˚C. It is then heated to 99.0˚C. How much alcohol will spill out of the beaker?
On the coldest day of the year in Chicago history (-33˚C) the height of the Sears tower was measured to be 1450 ft. What would the height have been if it were measured on the hottest (40.5˚C) day of the year? Assume the tower is made of steel (α = 12 X 10-6/˚C).
1/273 of the volume of the gas at STP per every ˚C
the volume of a gas is directly proportional to the Kelvin Temp.
This is only true assuming the pressure on the gas remains constant, which it often does not!
The effect of pressure on a gas while the temperature remains constant was first demonstrated by Robert Boyle:
Boyle’s Law: the volume of a gas varies inversely with the pressure on it!
When the pressure and the temperature changing, use the combined gas law to find how the volume reacts:
PV = P V
Pressure is measured in many ways:
760 mm Hg = 1 atm = Standard Pressure
When 2.00 L of a gas at STP is heated to 80.0˚C it expands to a volume of 2.50 L. How must the pressure have also changed?
V = 2.00 L
P = PVTk
T = 273˚K
P = 760 mm Hg
T = 353˚K
=(760 mm)(2.00 L)(353˚K)
V = 2.50 L
∆P = ?
∆P = P - P = 786 mm - 760 mm =
26 mm Hg
1) A certain gas occupies 3.00 L at 10.0˚C and 778 mm Hg. What volume will it occupy when the temperature is raised to 100.0˚C and the pressure is lowered to 750 mm Hg?
2) The density of air is 1.29 g/L at STP. What will the density of air be at 50.0˚C and a pressure of 1.23 atm?
3) If a gas will occupy 2.00 L at 25.0 ˚C and 775 mm Hg, what temperature change will bring it to 1.90 L if the pressure drops to standard?
1) A steel gas tank is filled to the brim with 56.0 L of gasoline on a day when the air temperature is 5.0 ˚C. The car is then immediately placed in garage where the temperature is 22.0˚C. How much gas will spill out of the tank?
2) A washer has a 2.000 cm hole in it at room temperature (20.0˚C). When it is plunged into boiling water the diameter is 2.003 cm. What is the washer made of?
3) One mole of a gas will occupy 22.4 L at STP. What volume will one mole of hydrogen occupy at -35.0˚C and 185.0 kPa?
A plumber wants to fit a copper ( = 16.8 X 10-6/ ˚C) ring onto a pipe that is 4.000 cm in diameter. The hole in the ring is only 3.980 cm. The ring and the pipe are at room temperature (20.00˚C). To what temperature must the plumber heat the ring in order to get it to just slip over the pipe?
A large, calibrated Pyrex ( = 3 X 10-6/˚C) beaker is filled with 1000.0 cm3 of water ( = 210 X 10-6/˚C) at 20.00˚C. If the flask and water are then heated to 95.00˚C, what will the new reading be?