EnergyEnergy

Two Types of EnergyTwo Types of Energy

Potential EnergyPotential Energy– Stored energyStored energy– We only see changes during Phase changesWe only see changes during Phase changes

Kinetic EnergyKinetic Energy– Energy of motionEnergy of motion– Changes whenever there is a change in Changes whenever there is a change in

temperaturetemperature

Temperature is a measure of Kinetic EnergyTemperature is a measure of Kinetic Energy

What is Absolute Zero?What is Absolute Zero?

There are two temperature scales There are two temperature scales that we need to knowthat we need to know

CelsiusCelsius– Water Water freezesfreezes at 0 at 0 ooCC– Water Water boilsboils at 100 at 100 ooCC

KelvinKelvin– K = K = ooC + 273C + 273– Water Water meltsmelts at 273 K at 273 K– Water Water condensescondenses at 373 K at 373 K

What do you notice about the What do you notice about the sizesize of a of a Kelvin and Celsius degree?Kelvin and Celsius degree?

The first equation you need to work The first equation you need to work with Heatwith Heat

Whenever there is a change in temperatureWhenever there is a change in temperature– From Table T in your Reference TablesFrom Table T in your Reference Tables– q = m c q = m c T T– Heat, mass, specific heat capacity, and temperature Heat, mass, specific heat capacity, and temperature

changechange– Specific heat CapacitySpecific heat Capacity for water is listed on for water is listed on Table BTable B..– Remember that Remember that T represents two numbers T represents two numbers

What are the two numbers?What are the two numbers?

What order should they be in?What order should they be in?

– About the sign of q…About the sign of q…Can it be negative?Can it be negative?

What would that mean?What would that mean?

An example using the first equationAn example using the first equation

Example: How much heat is absorbed when 89 Example: How much heat is absorbed when 89 grams of water is heated from 298 K to 330 grams of water is heated from 298 K to 330 K?K?

The second equation you need has The second equation you need has to do with a phase changeto do with a phase change

solid to a liquid = melting (a.k.a. fusion)solid to a liquid = melting (a.k.a. fusion)

Liquid to a solid = freezingLiquid to a solid = freezing

Equation from Table T in your Reference Equation from Table T in your Reference TablesTables– q = m Hq = m Hf f

– Heat, mass, Heat of Fusion– Heat of Fusion for water is listed on Table B.

An example using the Heat of An example using the Heat of Fusion of WaterFusion of Water

What is the mass of a sample of ice that What is the mass of a sample of ice that requires 13,400 J of heat to melt?requires 13,400 J of heat to melt?

The last equation – for the other The last equation – for the other phase changephase change

Liquid to a gas = boilingLiquid to a gas = boiling

Gas to a liquid = condensationGas to a liquid = condensation

Equation from Table T in your Reference Equation from Table T in your Reference TablesTables– q = m Hq = m Hvv

– Heat, mass, Heat of Vaporization– Heat of Vaporization for water is listed on

Table B.

An example using the Heat of An example using the Heat of Vaporization of WaterVaporization of Water

What is the mass of a sample of liquid water What is the mass of a sample of liquid water that requires 13,400 J of heat to boil that requires 13,400 J of heat to boil

completely?completely?

Now for another example, and I am Now for another example, and I am not telling you which equation to not telling you which equation to

useuse

A sample of water that has a mass of 87.4g. A sample of water that has a mass of 87.4g. if it releases 1249 J of heat and had an if it releases 1249 J of heat and had an original temperature of 89original temperature of 89ooC, what is the final C, what is the final temperature of the water?temperature of the water?

A more interesting exampleA more interesting example

A sample of ice at its freezing point has a A sample of ice at its freezing point has a mass of 45.0 grams. How much heat is mass of 45.0 grams. How much heat is needed to melt the sample and then raise needed to melt the sample and then raise its temperature to 354 K?its temperature to 354 K?

Is this endothermic or exothermic?Is this endothermic or exothermic?

Draw a Heating/cooling curve that would Draw a Heating/cooling curve that would be associated with this question. be associated with this question.

Let’s brush up on a couple of Let’s brush up on a couple of conceptsconcepts

What is happening to the particles of a What is happening to the particles of a substance while the temperature is substance while the temperature is increasing?increasing?What is happening to the particles of a What is happening to the particles of a substance when it is…substance when it is…– Melting?Melting?– Freezing?Freezing?– Boiling (Vaporizing)?Boiling (Vaporizing)?– Condensing?Condensing?

– Subliming (sublimation)?– Depositing (deposition)?

What is a Calorimeter?What is a Calorimeter?

An insulated container used for measuring An insulated container used for measuring temperature changes temperature changes Translation … a Styrofoam cup is usually Translation … a Styrofoam cup is usually used in our classes. used in our classes. The idea is:The idea is:– Use water to catch all of the heat given off by Use water to catch all of the heat given off by

somethingsomething– Use our energy equations to determine the Use our energy equations to determine the

amount of energy change in the wateramount of energy change in the water

An exampleAn example

A piece of metal with a mass of 24.0g is added A piece of metal with a mass of 24.0g is added to a 100.0g sample of water. The initial to a 100.0g sample of water. The initial temperature of the water is 20.0temperature of the water is 20.0 o oC and the C and the initial temperature of the metal is 100 initial temperature of the metal is 100 ooC. If the C. If the final temperature of the water-metal final temperature of the water-metal combination is 40.3combination is 40.3ooC, what is the specific heat C, what is the specific heat of the metal?of the metal?