Heat and Energy

Heat and Energy

Molecules and atoms

~ trillions in a dust particle.

~ always in motion……always.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Kinetic Theory

Temperature ~

The average kinetic energy of all of the molecules in a piece of matter.

Average speed.

Length of arrow indicates speed, or kinetic energy

Thermal Energy ~

The sum of all of the kinetic and potential energy in a piece of matter.

More thermal energy, because there are more molecules.

Question #1

Which has the higher temperature, a red hot nail, or a tub of ice water?

Question #1

Which has the higher temperature, a red hot nail, or a tub of ice water?

The nail, because each molecule is moving, on average, faster than the average molecule in the tub of ice water. There may be a few molecules in the ice water that are still moving faster than a few in the red hot nail.

Question #2

Which has a higher thermal energy, a red hot nail, or a tub of ice water?

Question #2

Which has a higher thermal energy, a red hot nail, or a tub of ice water?

The tub of ice water, because even though each molecule is moving, on average, more slowly; there are a lot more molecules.

Higher Temperature

Higher Kinetic Energy

Higher Thermal Energy

Generally Speaking

Heat is the movement of thermal energy from an area of high temperature, to an area of low temperature.

Question…Does heat rise?

Heat is the movement of thermal energy from an area of high temperature, to an area of low temperature.

Question…Does heat rise?

It can, but it will move in any direction. Hot AIR will rise, because it is less dense than cold air.

Specific Heat ~ This is a tough concept, I would pay a LOT of attention here (and you know who you are!!)

Specific heat is the amount of energy needed to raise the temperature of 1-kg of a mass, by 1 degree centigrade, or by one Kelvin.

Specific Heat ~ This is a tough concept, I would pay a LOT of attention here (and you know who you are!!)

Specific heat is the amount of energy needed to raise the temperature of 1-kg of a mass, by 1 degree centigrade, or by one Kelvin.

Aluminum has a very low specific heat, so it will heat up very quickly, and cool down very quickly.

Water has a very high specific heat, so it will heat up slowly, and it will cool down slowly.

Calculate Specific Heat

m = mass

C = specific heat

Ti = initial temperature

Tf = final temperature

Q = change in thermal energy

Q = m • (Tf - Ti) • C

Calculate Specific Heat

m = mass

C = specific heat

Ti = initial temperature

Tf = final temperature

Q = change in thermal energy

Q = m • (Tf - Ti) • C

What is the change in thermal energy (Joules), of a 2.5 kg mass, that goes from 45ºC to 55ºC, and has a specific heat of 235 J/(kg • K)?

Q = m • (Tf - Ti) • C

What is the change in thermal energy (Joules), of a 2.5 kg mass, that goes from 45ºC to 55ºC, and has a specific heat of 235 J/(kgK)?

Tf 55º C + 273 = 328 K

Ti 45ºC + 273 = 318 K

Q = 2.5 kg • 10 K • 235 = 5,875 J

Q = m • (Tf - Ti) • C

What is the change in thermal energy (Joules), of a 2.5 kg mass, that goes from 45ºC to 55ºC, and has a specific heat of 235 J/(kgK)?

Tf 55º C + 273 = 328 K

Ti 45ºC + 273 = 318 K

Q = 2.5 kg • 10 K • 235 = 5,875 J

If you got it, smile broadly!!

Water has a specific heat of 4,186 [J/(kg•K)]

If you are heating up 1,000 ml of water for a whole bunch of Ramen Noodles, and the water comes out of your tap at 10ºC, how many Joules of energy will you need to provide?



1st ~ write down the formula

Q = m • (Tf - Ti) • C




Q = m • (Tf - Ti) • C

2nd ~ substitute in what you know.

Joules = ?

Mass = 1,000 ml water = 1,000 cm3 = 1,000 grams = 1 kg

Tf = (100ºC + 273) = 373 K

Ti = (10ºC + 273) = 283 K

C = 4,186




Q = m • (Tf - Ti) • C

2nd ~ substitute in what you know.

Joules = ?

Mass = 1,000 ml water = 1,000 cm3 = 1,000 grams = 1 kg

Tf = (100ºC + 273) = 373 K

Ti = (10ºC + 273) = 283 K

C = 4,186

Q = 1 kg • 90 K • 4,186 [J/kg•K)] = 376,740 J

You are out camping with friends, and you want some hot water for cocoa. They want to put a pot on the fire, but you paid attention in Mr. Monroe’s science class, and you want to make sure that you don’t just burn all the wood for nothing. Your question is whether or not you can heat the water, to 90ºC, with the wood on hand.

Water has a volume of 2.5 liters

Water has a specific heat of 4,184

Water’s temperature is 5ºC

You have 10 pounds of wood

The wood has about 10,000 Joules per pound

Q = m • (Tf - Ti) • C

Q = Joules needed

M = 2.5 kg

Tf = 278 K

Ti = 363 K

C = 4,186

Joules Needed = 2.5 kg • 85 K • 4,186 = 103,275 Joules

You only have

10 pounds 10,000 Joules

--------------- x ------------------ = 100,000 Joules (almost enough)

1 pound

Thermal Energy Transfer (heat)

Conduction ~ the transfer of heat through the direct contact of particles.



QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.



Convection ~ the transfer of heat through the movement of the particles themselves.






Radiation ~ the transfer of energy through electromagnetic waves






Radiation ~ the transfer of energy through electromagnetic waves



Scenario one. The temperature outside is 100ºF. You want to stay cool, so what might you do.

Scenario one. The temperature outside is 100ºF. You want to stay cool, so what might you do.

a. You might use an umbrella, to shield from the Sun

b. You might wear white.

Scenario Two. The temperature outside is -20ºF. You want to stay warm, so what do you do?

a. You may wear black, to absorb the Sun’s rays

b. You may wear layers of clothing, to use the insulating powers of the trapped air to slow the inevitable, irreversible, insatiable and irrevocable transfer of heat.

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Heat and Energy