Temperature

• Defined as the measure of the average kinetic energy of the molecules in a sample.

1) Increase temperature = increase in KE

Temperature Scale

Scale Water Freezes

Water Boils

Who Uses

Fahrenheit

Celsius

32°F

0°C

212°F

100°C

U.S. & one other country

Everyone else. Scale used in science

Thermal Expansion1) Most materials expand when heated

because as the molecules move around they move apart

2) Thermal expansion is the principle behind thermometers.

a) expansion of the liquid inside the tube is proportional to the change in temperature

3) Thermal expansion is used in thermostats.

a) Thermostats use a bimetallic strip to open and close the circuit.

• Explain why running a spaghetti jar lid under hot water will allow a person to open the lid easier than when the jar is cold.

• Underline and use the following terms/ phrases in your explanation.

1) thermal expansion

2) increase temperature

3) increase kinetic energy

4) move apart

Heat1) Defined as the flow of thermal energy.

2) Heat only exists where there is a difference in temperature.

3) Heat always flows from hot to cold.

4) Unit of heat is the calorie.

a) calorie is defined as the quantity of heat needed to raise the temperature of 1 gram of water by 1°C

Changes in Heat1) Temperature AVERAGE KE of a sample

2) Thermal Energy sum (total) of all KE and PE of the molecules in a substance (PE comes from energy in bonds)

a) depends on:

1) mass amount of matter

2) temperature

3) amount of energy the material can hold

Specific Heat1) Defined as a property of a substance that tells

how much the temperature goes up when a given amount of heat is applied.

2) The higher the specific heat, the harder it is to raise the objects temperature

Substance Specific Heat

calorie/g°C

Water 1.00

Ice 0.493

Aluminum 0.215

Silver 0.052

Gold 0.031

Very difficult to raise the temp of water, reason why water is used as a coolant

Easy to raise the temp because of the low specific heat

The Heat Equation

Q = mcΔT

Heat energy(calorie)

Mass (g)

Specific Heat (calorie/g°C)

Change in temp (°C)ΔT = Tf – Ti

If ΔT is negative = heat is lost, Q is negative

If ΔT is positive = heat was gained, Q is positive

Q = mcΔTSample Problem: How much heat is needed

to raise the temp of 250 g of water from 20°C to 40°C?

Q = ??

m = 250 g

c = 1.00 calorie/g°C

ΔT = 40 – 20 = 20°C

Q = (250)(1.00)(20)

Q = 5000 calories

• When 300 calories of energy is lost from a 125g object, the temp increases from 40 to 45C. What is the specific heat of this object?

Q = 300 calories

m = 125 g

c = ??

ΔT = 45 – 40 = 5°C

300 = (125)(c)(5)

300 = (c)(625)

300 = c

625

0.48 = c

• 1200 calories of heat energy is added to a liquid with a specific heat of 0.57. If the temperature increases from 20 to 33°C, what is the mass of the object?

Q = 1200 calories

m = ???

c = 0.57 calorie/g°C

ΔT = 33 – 20 = 13°C

1200 = (m)(0.57)(13)

1200 = (m)(7.41)

1200

7.41

162 g = m

= m

Flow of Heat and Equilibrium1) First Law of Thermodynamics

energy in a closed system is conserved

heat loss = heat gain

When the ice cube goes into the coffee, the amount of heat lost by the coffee will equal the heat gained by the ice cube.

2) Thermal Equilibrium results when heat flows from a hot object to a cold object until they are at the same temperature.

a) heat flow stops once objects reach thermal equilibrium.

Your grandmother in Ireland send you her favorite cookie recipe. Her instructions say to bake the cookies at 190.5°C. To what °F

temp would you set the oven to bake the cookies

• Formula: F = (9/5 X C) + 32

F = (9 X 190.5) + 32 (1714.5) + 32 342.8 + 32 5 5

375°F

2) Your father orders a fancy oven from England. When it arrives, you notice that

the temp dial is calibrated in °C. You wish to bake a cake at 350°F. At what temp will you

have to set the dial on the new oven?

Formula: C = 5/9(F – 32)

C = 5(350 – 32) 5(318) 1590 177

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3) Your new German car’s engine temp gauge reads in °C, not °F. You know that

the engine temp should not rise above 225°F. What is the corresponding °C temp

on you new car’s gauge?

Formula: C = 5/9(F – 32)

C = 5(225 – 32) 5(193) 965 107

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A scientist wishes to generate a chemical reaction in his lab. The temp values in his manual are given in °C. However, his lab

thermometers are calibrated in F. If his need to heat his reactant to 232°C, What temp will he

need to monitor on his lab thermometers?

Formula: F = (9/5 X C) + 32

F = (9 X 232) + 32 (2088) + 32 417.6 + 32

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450°F

You phone a friend who lives in Denmark and tell him the temp today only rose to 15°F. He replies that you must have enjoyed the warm weather.

Explain his answer.

He was thinking that the temp was 59F (because 15°C = 59°F). He did not understand that 15°F is WAY below freezing.

A gas has a boiling point of -175°C. At what Kelvin temp would this gas boil?

Formula: K = C + 273

K = -175 + 273

K = 98

A chemists notices some silvery liquid on the floor in her lab. She wonders if someone accidentally broke a Hg thermometer. From her tests she find out that the melting point for the liquid is 275K. A book says the

melting point of Hg is -38.87 C. Is this substance Hg?

Formula: K = C + 273

K = -38.87 + 273K = 234

No, the liquid is not Hg b/c the melting points are different.

You are at a science camp in Fl. It is August. The 1st question on the quiz involves a

thermometer that reports the current temp as 90°. You need to state which temp scale the

thermometer is calibrated. Which scale do you pick?

90°C is almost boiling so not that one.

90°C is equal to 363K which is also almost boiling so its not Kelvin.

90°F is warm but no where near boiling, pick this one!

1) The weatherman tell you that today will reach a high of 45°F. Your friend in Sweden

asks what the temperature will be in °C. What value would you report to your friend?

Formula: C = 5/9(F – 32)

C = 5(45 – 32) 5(13) 65 7.2

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