Energy

1. Energy

2. Energy Storage and Transfer • Metaphor to describe energy storage and transfer – that of money. We store money in accounts at the bank. We can have checking accounts, savings accounts, certificates of deposit, etc. These accounts store money. There is nothing different about the money in checking and savings accounts. This money can be transferred back and forth in the bank without changing the nature of the money or the total quantity of money that resides in the collection of accounts that is attached to your name. • The same is true of energy. We use different “accounts” to help us keep track of energy as its transfer causes change in the objects or in their arrangement. As with money, nothing about the energy itself has changed.

3. Thermal Energy (Eth) • The energy stored by moving particles. The faster the particles move, the higher the thermal energy. Temperature is a measure of thermal energy. • Which has the higher thermal energy?

4. Phase Energy (Eph) • The energy stored in the system due to the arrangement of particles. Gases have the most phase energy and solids have the least. • Which has the most Phase Energy? )) )) )) )) Solid Liquid Gas

5. Chemical Energy (Ech) • The energy due to attractions of atoms within the molecules. • Right now we are not dealing with any type of chemical changes so there will be no changes in chemical energy.

6. Energy Transfer • Energy is transfer between system and surroundings in 3 ways • Working (W) • Heating (Q) • Radiating (R) • ∆E = W + Q + R

7. Energy Bar Charts Consider this example A cup of hot coffee cools as it sits on the table. 1. Determine what is in the system • Everything else makes up the surroundings cup coffee

8. 2. Decide whether Ech is involved • In this case, you start with coffee and end with coffee; particles are not rearranged to form new substances • So, ignore Ech for now.

9. 3. Assign values to Eph depending on the phases • Due to interactions between particles, the energy stored due to the arrangement of particles is ranked:solids < liquids < gases • We choose to represent these phases by using: • Solids = 1 bar • Liquids = 2 bars • Gases = 4 bars cup coffee

10. 4. Assign values to Eth depending on the temperatures. • Use 4 bars for hot coffee and 2 bars for room temp coffee • Other values might also work; try to be consistent in your representations cup coffee

11. 5. Label the total number of bars for initial and final. Show energy transfer. • Final situation has 2 less bars of E than initial; 2 bars had to leave the system cup coffee

12. Define your system. Decide whether Ech is involved. Assign values to Eph depending of the phases(solid = 1 bar; liquid = 2 bars; gas = 4 bars). Assign values to Eth depending on the temperatures. Label the total number of bars for initial and final. Show energy transfer.