Heat Review

Review relationship between Temperature and Heat:

Heat TemperatureThermal energy that is

transferred!!

Measure of the average Kinetic energy of the molecules in a

substance!

Is mass dependent!! Is not mass dependent!!

Cannot be measured directly!!Only by the changes in

temperature they cause!!

Can be measured directly!! With a thermometer!!

Measured in Joules(J) Measured in oC, oF, or K

Defined…. Defined….

Does it depend on Mass? Does it depend on Mass?

Can you measure it? Can you measure it?

Units??? Units???

3 Ways to Transfer Heat1. Conduction---direct contact

2. Convection—transfer of heat in liquids and gases!!

3. Radiation—transfer through empty space!!

Discuss Heat Transfer Mechanisms!!!

Look at this graph and discuss in terms of temperature!!

Which is the “HOT” and which is the “COLD”?

What is happening to the Hot water? Why?What is happening to the Cold water? Why?

Is the final temperature closer to the initial hot water temperature or closer to the initial cold water temperature????

Why??????

Which has more mass, the hot water or the cold water??By how much???How do you know???

Is the final temperature closer to the initial hot water temperature or closer to the initial cold water temperature????

Why??????

Which has more mass, the hot water or the cold water??By how much???How do you know???

Is the final temperature closer to the initial hot water temperature or closer to the initial cold water temperature????

Why??????

Which has more mass, the hot water or the cold water??By how much???How do you know???

What is Thermodynamics?

The study of the relationship between heat, work and other

forms of energy!!

3 Laws of Thermodynamics:

• 1st Law—Conservation of Heat Energy

• 2nd Law—Law of Entropy• 3rd Law—Absolute Zero

1st Law—Conservation of Heat Energy

• Basically a restatement of the law of Conservation of Energy.• Heat Engines—convert thermal

energy into useful work.• Heat Lost = Heat Gained

2 types of heat engines:

• Internal Combustion Engine– Burning happens inside

the engine.

• External Combustion Engine– Burning happens outside

the engine and then heat is transferred to the engine.

2nd Law—Law of Entropy

• Heat will not flow from low to high temperatures spontaneously(on its own).

• Entropy– disorder• Ex. A glass jar is “order”. Throw it against a wall, and

you have created “disorder”. You have increased its entropy.

• Heat engines cannot be built that convert all heat energy into useful work. There will be exhaust.

3rd Law—Absolute Zero

• Many times, included with 2nd Law.• Absolute Zero—temperature at which all

molecular motion stops.• Zero Kelvin

• Impossible to reach. Why? Think about what 2nd Law states!!!!!!

Phases and Changes in Phase

• 3 states of Matter:

1. Solids—definite shape and volume

2. Liquids—definite volume, no definite shape

3. Gases—no definite shape or volume

• Anytime a substance changes from one state to another, a phase change has occurred.

When do phase changes happen?

• Phase changes happen at very specific temperatures.

Solids Liquids Gases

Melting Point(or Freezing Point)**Same Temperature**

Boiling Point

WaterWater melts and

freezes at the same temperature!!What is that

temperature(in oC)?0 oC

If you are adding heat, it melts at

0 oC. If you are

removing heat, it freezes at 0 oC.

At what temperature does Ice melt?

At what temperature does liquid water

freeze?

How do you know which it is going to do?

You never know when you may need that bit of

“useless” information!!H2O melts/freezes at 0 oC!H2O boils/condenses at

100 oC!

Phase Change Diagrams• A phase diagram is common way to represent

the various phases of a substance and the conditions under which each phase exists.

• Phase change diagrams represent a substance with heat being added(or removed) at a constant rate!!

At point A, the beginning of observations, the substance exists in a solid state. Material in this phase has ___definite ___ volume and ______definite __ shape. With each passing minute, ___heat______ is added to the substance.

This causes the molecules of the substance to ____move____ more rapidly. At point B, the temperature of the substance is ___70___°C. The solid begins to __melt____.

At point C, the substance is completely ___melted_________ or in a ____liquid_______ state. Material in this phase has ____definite___________ volume and __no definite_ shape.

The energy put to the substance between minutes 5 and 9 was used to convert the substance from a __solid____ to a ____liquid___. This heat energy is called the heat of fusion.

Between 9 and 13 minutes, the added energy increases the __temperature______ of the substance. During the time from point D to point E, the liquid is _vaporized__. By point E, the substance is completely in the __gas_____ phase.

Material in this phase has _no definite__ volume and _no definite _ shape. The energy put to the substance between minutes 13 and 18 converted the substance from a _liquid_________ to a ____gas_______.

This heat energy required to convert a liquid to a gas is called the heat of vaporization. Beyond point E, the substance is still in the _____gas___ phase, but the molecules are moving ____more rapidly__ as indicated by the increasing temperature.

Which of these three substances was likely used in this phase change experiment?

Substance Melting point Boiling point

Bolognium 20 °C 100 °C

Unobtainium 40 °C 140 °C

Foosium 70 °C 140 °C

m.p.

b.p.

TPhase

Solid Liquid Gas

Melting Pt. Boiling Pt.

Is heat being added or removed???

Phase

Phase

Melting Pt.

Boiling Pt.

T

T

T

Solid

Liquid

Gas

Phase

Phase

T

T

T

Solid

Liquid

GasBoiling Pt.

Melting Pt.

If you take a block of ice at -25 oC and place it on a stove which is turned on high(which is adding heat at a constant rate, what happens????

ARE YOU SURE????

When you add heat to something, one of two things will happen, but they will

never happen at the same time!!!!

1. Substance will change temperature.2. Substance will change phase.