1

Temperature measures the average kinetic energy of

the molecules. Heat measures the average kinetic energyAnd incorporates mass.

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HEAT AND TEMPERATURE

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Heat versus temperature

Temperature A measure of hotness

or coldness of an object Based on average

molecular kinetic energy

Heat Based on total internal

energy of molecules Doubling amount at

same temperature doubles heat

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How do we measure temperature?

Think about using a thermometer…..

How does the thermometer know how hot the substance is?

The molecules of the substance bump into the thermometer and transfer energy. How often and how hard they bump into the thermometer are directly related to their speed. Temperature turns out to be related to the average speed of the molecules in a substance

Temperature is not a measure of the total amount of energy in an object.

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SISI

joulejoule

USCSUSCS

Units of EnergyUnits of Energy

caloriecalorie

4.184 J = 1 cal4.184 J = 1 cal

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Units of Energy (heat energy)

Units of Energy (heat energy)

1000 calories = 1 kilocalorie1000 calories = 1 kilocalorie

1000 calories = 1 Calorie1000 calories = 1 Calorie

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

a. K = C + 273 (10C = 283K)

b. C = K – 273 (10K = -263C)

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

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

Specific Heat

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

Land heats up and cools down faster than water

b. Specific heat is the amount of heat required to raise the temperature of 1 kg

of a material by one degree (C or K).

1) C water = 4.184 J / g C

2) C sand = 0.664 J /g C

This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

How to calculate changes in thermal energy

Q = m x T x Cp

Q = change in thermal energy – must be in joules – can be positive (+) or negative (-)

m = mass of substance – must be in grams (g)

T = change in temperature (Tf – Ti) - (Kelvin) or (Celsius)

Cp = specific heat of substance (J/g • ˚C) or

(J/g• K)

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HEAT FLOW PROBLEMSA 4.0 g sample of glass was heated from 274 to 314 K . And was found to have absorbed 32 J of energy as heat. What is the specific heat of glass?

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Density

Density compares the mass of an object to its volume

D = mass = g or g

volume mL cm3

Note: 1 mL = 1 cm3

Gold is very dense - it feels very heavy for its size.

D = 19.3g/cm3

Each substance has its own density. A larger amount will still have the same density because it will be an equivalent fraction.

Metal Density

Gold 19.3

Silver 10.5

Platinum 21.4

Palladium 12.0

Copper 9.0

9ct 10.9 to 12.7

14ct 12.9 to 14.6

18ct Yellow 15.2 to 15.9

18ct White 14.7 to 16.9

22ct 17.7 to 17.8

Sterling Silver 10.2 to 10.3

950 Platinum 20.1

If you pack more mass into the same volume, it is more dense.

Draw a picture on your handout that represents this principle.

If you pack the SAME mass into a SMALLER volume, it is MORE dense

Draw a picture on your handout that represents this principle.

Just because something has more mass DOES NOT mean it is more DENSE.

You can make something have less dense by increasing the volume until it is more than the mass.

Principle 4

RULE

Anything with a density less than one will float in water. If there are numbers to the left of the decimal it will sink!

So why do ships float ?

The density of steel is 7.8 g/cm3

The density of waters 1 g/cm3

Think of a steel ship as a can that is empty and watertight. The majority of its space is taken up by nothing more than air which has a specific gravity of about 0.00129. So if a make a ship that is like a can,

empty inside and watertight it floats. Its volume sufficient that it causes its specific gravity to remain below 1.0 even after adding the weight of

its contents. The steel ship will remain afloat as long as its density remains

below that of water. The problem is that if water is allowed to enter the ship it would sink. Ships made of steel have to be sealed so water can

not get in and increase its density. Steel can float only because of the way it is shaped, the space

it takes up, and the seal that keeps its watertight. The ability of steel to float is the ability of people to shape metal and solve problems by

examining outcomes.

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Learning Check D1

Osmium is a very dense metal. What is its

density in g/cm3 if 50.00 g of the metal occupies

a volume of 2.22cm3?

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Volume Displacement

A solid displaces a matching volume of water when the solid is placed in water.

33 mL

25 mL

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Learning Check

What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?

1) 0.2 g/ cm3 2) 6 g/m3 3) 252 g/cm3

33 mL

25 mL

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Solution

2) 6 g/cm3

Volume (mL) of water displaced = 33 mL - 25 mL = 8 mL

Volume of metal (cm3) = 8 mL x 1 cm3 = 8 cm3

1 mLDensity of metal =

mass = 48 g = 6 g/cm3

volume 8 cm3

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Density as Conversion Factors

A substance has a density of 3.8 g/mL.

Density = 3.8 g/mL

Equality 3.8 g = 1 mL

Conversion factors.

3.8 g and 1 mL

1 mL 3.8 g

lecturePLUS Timberlake 30THINGS TO REMEMBERThe density of water is 1.00 g/ml at 0˚ C

Has an object heats up it becomes less dense.

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GRAPHS

1. When two quantities are directly proportional to each other, if dividing by the other gives a constant value.

Example K = Y / X

2. Students will graph speed vs distance. The time is constant.

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10 mi/hr

20 mi/hr

30 mi/hr

40 mi/hr

50mi/hr

60 mi/hr

70 mi/hr

Speed Distance

Calculate the distance if the time remains constant at ( 2 hours)

Speed = Distance / Time

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Graph speed verses time. The distance will remain constant at 200 miles.

speed = distance / time

10 mi/hr

20 mi/ hr

30 mi/hr

40 mi/hr

50 mi/hr

60/ mi/hr

70 mi/hr

speed time

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Mass and volume are related directly.

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Volume and pressure are related indirectly.

Graph of an indirect relationship

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Exponential RelationshipsOne variable goes up slowly and the other very quickly.

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Which swimmer is faster (red, green or blue)?What happened to the green swimmer between 10 and 20 seconds?