LOL Diagram Notes.ppt

1. LOL Diagrams
How to represent the
role of energy in
physical change
© Modeling Instruction in Chemistry

2. Constructing an LOL Diagram
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

3. 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.

4. Assign values to Eph
 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 box
 Liquids = 2 boxes
 Gases = 4 boxes

5. Assign values to Eph
 Use two Eph bars before and after
cup
coffee

6. Choose bars for Eth depending
on temperature
 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

7. Now show energy transfer
 Final situation has 2 less bars of E than
initial; 2 bars had to leave the system

8. Now, consider phase change
 A tray of ice cubes (-8 ˚C) is placed on the counter
and becomes water at room temperature
 What do we know about the situation?
 The system is the tray of ice cubes.
 The solid water turns to liquid water - no change in Ech
 The Eph increases (solidliquid)
 The Eth increases (temp rises)
 Now represent these changes in bar graph.

9. Initial & Final States
 A tray of ice cubes (-8 ˚C) is placed on the
counter and becomes water at room
temperature

10. A tray of ice cubes (-8 ˚C) is placed on the counter
and becomes water at room temperature
Tray of
ice
5 – 3 = 2
NOTE: Since the ice does not chemically change while melting we
need to keep the Ech the same, other numbers of boxes can work
as long as it is the same from initial to final.

11. Notes to keep in mind:
 We only use whole boxes.
 We must have at least one box in each
section, even for chemical energy.
 If the chemical energy is not changing then
just keep it the same in both diagrams.
 It is always final – initial when determining
length of the arrows.
 If it is negative it should point out of the circle.
 If it is positive it should point into the circle.