Heat is the transfer of energy between

objects due to a temperature difference.

How do you think this transfer happens?

HEAT

The idea of a Calorie had been around for a

while, (amount of energy to raise 1 kg of water

1 degree Celsius)

and Joule made the following relationship (conversion)

4.186 J = 1 cal

This idea of energy being transferred by heat

needs some caution.

Heat is a transfer of energy, not energy itself

It is not a fluid or any substance

It is a change of internal or thermal energy

To be clear, there are 3 ideas that we need to distinguish

Temperature - this is the AVERAGE kinetic energy of the molecules

Internal energy - is the TOTAL energy of ALL the molecules

Heat - is the transfer of energy due to temperature difference.

**A B**

A and B are both equally dense pieces of iron

A has more mass than B

If these two objects are

in thermal equilibrium then

Which has a greater temperature

A. A does

B. B does

C. they are the same

If these two objects are

in thermal equilibrium then

Which has a greater thermal

energy

A. A does

B. B does

C. they are the same

Carrying on with this idea of internal energy

If I have a substance with N molecules, with each

molecule having an average kinetic energy, I can

add all of this energy up and get an Internal energy

From kinetic theory this parenthetical term is

proportional to temperature (3/2 kT)

This then is the internal energy of an

ideal monatomic gas.

or

Specific Heat

Now that we have an idea of where the energy

can go, (internal energy = motion of molecules)

we can quantify that energy transfer due to

temperature difference = heat flow.

As I'm sure you guessed, (or knew) different substances require more heat to change their internal energy. We define an intrinsic property of a substance that quantifies this change in temperature from heat flow as: Specific Heat.

This is the equation that describes the

amount of heat required to raise a mass, m,

a certain amount of temperature.

Note the term 'c' is the specific heat of an

object.

Things to note:

Temperature can be either C or K because it is a change and they both use the same step size

Mass is in kg

and c needs to be in J/kg C to make Q be in energy units of J.

If water has a c=4186 J/kg c ,

how much energy is needed

to raise 1 kg of water 10 degrees

A. 418.6 J

B. 4186 J

C. 41860 J

Calorimetry is the exchange of energy between

two (or more) objects.

It needs:

An isolated system - no energy at all is transferred out of the system

Some form of heat transfer

be careful of phase changes

Calorimetry

Latent Heat

No temperature change, yet heat flow with phase change

Note: it can be plus or minus +,-

To melt 1 kg of water 333 kJ is needed

to Boil 1 kg of water 2260 kJ is needed

How much heat is removed from 5.0 kg of liquid lead at its melting point of 327 C to cool it down to room temperature (20 C)?

A. 12.5 kJ

B. 187 kJ

C. 200 kJ

D. 212 kJ

E. 225 kJ

Q = -212,050 J

conduction

Quantitatively, we can discuss the rate of heat flow between

two objects.

Q is obviously the heat, and t is the time

k here is conductivity constant ( it is usually a kappa)

A is cross sectional area, l is the distance the heat flows

through.

Example windows

A convection process

is a transfer of heat, by a bulk flow

of molecules that heat up surrounding

ones.

Convection

The temperature of an object really influences the

rate of radiation. Notice the power the temperature

is raised to.

Sigma is a constant (small number)

e is emissivity, it ranges from 0-1

A is area

Radiation

Radiant heat is actually electromagnetic waves. You will get into that, sooner than you think, but not this semester.

That's all we have for this chapter

take away concepts

Internal energy

Calorimetry/latent heat

Modes of heat transfer

**A. Conduction**

B. Convection

C. Radiation

B. Convection

C. Radiation

**A range on a stove heats**

food by:

food by:

**A Heat lamp works by**

**Forced air heater**

works by

works by

Heat

Internal Energy

Specific heat

Latent Heat

Calorimetry

Modes of heat transfer

conduction, convection, radiation

(+/-)

"what is latent heat and how is it significant? "

"don't understand question 2 from the pre-quiz. "T/F heat, temp, and internal energy are all one in the same." What is different?"

"can you explain what specific heat is?"

"I'm a little confused by the difference between conduction and convection. Aluminum foil in the oven hardly absorbs any heat, is that convection? Also, why is styrofoam the best type of container to use when eating ice cream? It traps heat or lack of heat very well but is that the same kind of concept as aluminum foil?"

"Could you explain more on conduction and convection"

"When does convection factor into heat and the transfer of it?"

"Can you explain emissivity? "

"the Stefan-Boltzman equation. I'm a little confused about what all the different symbols mean in the equation."

"Does an ice cube make the water cooler or does the water make the ice cube hotter and melt?"

"Need help with recognizing the components of the equations for heat, some new terms like Calorie."