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Energy

Energy. Two Types of Energy . Potential 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?.

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Energy

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  1. Energy

  2. Two Types of Energy • Potential 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?

  3. 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 sizeof a Kelvin and Celsius degree?

  4. 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?

  5. 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?

  6. 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.

  7. 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?

  8. 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.

  9. 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?

  10. 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?

  11. 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.

  12. 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)?

  13. 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

  14. 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?

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