EndoExo

1
Endo/Exo
2
Chemical changes occur when

• We see
• Bubbles
• Precipitates
• Burns
• Changes color
• Changes temperature
• Change in temperaturethe reaction gets hot or
  cold

3
Physical changes occur when

• The substance is still the same substance
• The phase has changed
• Melted, evaporated, sublime
• Freeze, condense, deposit
• To change the phase of a substance, the
  temperature must be changed

4
TemperatureHmm

• In both physical and chemical changes, there can
  be a flow of heat between the system and
  surroundings.

5
Flow of Heat Between

• System
• The part of the universe we focus on
• Like a reaction or an ice cube thats melting
• Surroundings
• Everything else usually considered only what is
  right next to the system
• Like the beaker the reaction is in or your hands
  holding the ice cube

6
Heat can flow

• Into the system
• OR
• Out of the system
• We use two words to describe the direction of
  heat flow

7
Exothermic

• exo means outside
• therm means heat
• A change in which heat is given off from the
  system
• Heat flows out of the system
• Feels hot surroundings heat up

8
Endothermic

• endo means within
• therm means heat
• A change in which heat is absorbed from
  surroundings
• Heat flows into the system
• Feels cold surroundings cool down

9
Chemical Changes

• How do you tell if a chemical change is endo or
  exo?
• Gets hot exo
• Gets cold endo
• Physical changes can be trickierparticularly
  phase changes

10
Phase Changes

• Review What are the 3 states of matter?
• Solid definite shape, definite volume
• Liquid definite volume, shape of container
• Gas neither definite shape nor volume

11
Phase Changes

• What are some examples of phase changes?
• Melting
• Freezing
• Evaporating
• Condensing
• Sublimating
• Depositing

12
Phase Changes

• Melting, evaporating, sublimating
• Breaking bonds
• Increases ability of molecules or atoms to move
  freely
• Increase in energy
• To pull bonds apart you must put energy IN to the
  system
• Energy IN Endothermic

13
Phase Changes

• Freezing, condensing, depositing
• Forming bonds
• Decreases ability of molecules or atoms to move
  freely
• Decrease in energy
• Energy is given off from the system as bonds form
• Energy out Exothermic

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B A R F
R E A K B O N D S
B S O R B E D E
E L E A S E D E
O R M B O N D S
ENDO
EXO
15
Energy and Phases Review
Solid
sublimation
melting
deposition
freezing
Liquid
condensation
Gas
evaporation
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Energy and Phases Review

• Inside Arrows
• Exothermic (feels hot)
• Decreases energy of atoms/molecules (less freedom
  to move)
• Forming bonds (getting energy out of the system)

17
Energy and Phases Review

• Outside Arrows
• Endothermic (feels cold)
• Increases energy of atoms/molecules (more freedom
  to move)
• Breaking bonds (putting energy into the system)