Energy

Two Types of Energy Potential Energy Kinetic Energy Stored energy We only see changes during Phase changes Kinetic Energy Energy of motion Changes whenever there is a change in temperature Temperature is a measure of Kinetic Energy What is Absolute Zero?

There are two temperature scales that we need to know Celsius Water freezes at 0 oC Water boils at 100 oC Kelvin K = oC + 273 Water melts at 273 K Water condenses at 373 K What do you notice about the size of a Kelvin and Celsius degree?

The first equation you need to work with Heat Whenever there is a change in temperature From Table T in your Reference Tables q = m c  T Heat, mass, specific heat capacity, and temperature change Specific heat Capacity for water is listed on Table B. Remember that  T represents two numbers What are the two numbers? What order should they be in? About the sign of q… Can it be negative? What would that mean?

An example using the first equation Example: How much heat is absorbed when 89 grams of water is heated from 298 K to 330 K?

The second equation you need has to do with a phase change solid to a liquid = melting (a.k.a. fusion) Liquid to a solid = freezing Equation from Table T in your Reference Tables q = m Hf Heat, mass, Heat of Fusion Heat of Fusion for water is listed on Table B.

An example using the Heat of Fusion of Water What is the mass of a sample of ice that requires 13,400 J of heat to melt?

The last equation – for the other phase change Liquid to a gas = boiling Gas to a liquid = condensation Equation from Table T in your Reference Tables q = m Hv Heat, mass, Heat of Vaporization Heat of Vaporization for water is listed on Table B.

An example using the Heat of Vaporization of Water What is the mass of a sample of liquid water that requires 13,400 J of heat to boil completely?

Now for another example, and I am not telling you which equation to use A sample of water that has a mass of 87.4g. if it releases 1249 J of heat and had an original temperature of 89oC, what is the final temperature of the water?

A more interesting example A sample of ice at its freezing point has a mass of 45.0 grams. How much heat is needed to melt the sample and then raise its temperature to 354 K? Is this endothermic or exothermic? Draw a Heating/cooling curve that would be associated with this question.

Let’s brush up on a couple of concepts What is happening to the particles of a substance while the temperature is increasing? What is happening to the particles of a substance when it is… Melting? Freezing? Boiling (Vaporizing)? Condensing? Subliming (sublimation)? Depositing (deposition)?

What is a Calorimeter? An insulated container used for measuring temperature changes Translation … a Styrofoam cup is usually used in our classes. The idea is: Use water to catch all of the heat given off by something Use our energy equations to determine the amount of energy change in the water

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