1. Energy in Chemical Reactions
Making and breaking bonds….
Section 18.1

2. Particle Theory
Remember Democritus?...he is the “scary” looking greek from 2,000 years ago who believed in
ATOMS!
But he also thought atoms were the smallest particle out there
Scientists came back to Democritus’ idea and added to it.

3. Imagine you could take apart all the particles in this grain of salt.
Next you arrange all the particles in a row.
Would it be long enough to make a necklace?
How long would the row of particle be?

4. That’s more than 33 times the distance from the Earth to the Moon!
Democritus never found out the answer to his salty puzzle. Thousands of years later, we know just how long the row of salt particles would be…
metres
That’s more than 33 times the distance from
the Earth to the Moon!
All that from just one grain of salt!
What does tell us about the number and size
of the particles?

5. So next time you pour salt on your chips
The number of particles is very, very, very, very, very, very, very, very, very, very ,very, very big!
The size of the particles must be very, very, very, very, very, very, very, very, very, very, very small!
So next time you pour salt on your chips
spare a thought for all those tiny salt particles!

6. The Particle Model says…
Particles make up all matter and have mass
Particles have different shapes and sizes
Particles show ‘stickiness’, or the ability to bond with each other due to electrostatic attraction
Particles can have ‘poles’ of greater or lesser charge
Particles have energy which translates into motion

7. The particle model of a solid

8. The particle model of a liquid

9. The particle model of a gas

10. Solid particles...
- are very close together in a fixed arrangement
- have a small amount of energy
- vibrate but do not move
liquid particles…
- are close together but have no fixed arrangement
- more energy than solid particles
- vibrate and can move about
gas particles
- are far apart and have no fixed arrangement
- have a large amount of energy
- move rapidly in all directions

11. Water can be a solid, liquid, or a gas…
Its state depends on how much energy the water particles have.
If enough energy is added to or removed from the particles a change of state can occur.
ice
water
steam

12. Think what the PARTICLES are doing…
Draw a picture to show what is happening to the food coloring particles after they are dropped into a beaker of water…

13. Scientists find the particle model useful for two reasons.
First, it provides a reasonable explanation for the behavior of matter.
Second, it presents a very important idea—the particles of matter are always moving.
Matter that seems perfectly motionless is not motionless at all. The air you breathe, your books, your desk, and even your body all consist of particles that are in constant motion.
Thus, the particle model can be used to explain the properties of solids, liquids, and gases. It can also be used to explain what happens

14. Initial Conditioning…
Over the next 2 minutes, find an object and try to break it apart. Rules:
Objects cannot be mine
will not hurt anyone or anyone else’s property

15. What can we conclude… Breaking bonds requires ENERGY
So, just using logic, making bonds must releases energy
Pick one object and remember that breaking process as your ANCHOR

16. 2 H-H + O=O   2 H-O-H
Bonds: break old (use energy), recombine to form new bonds (release energy).
2 H-H bonds are broken, 2 O=O, costing energy, and 4 H-O bonds are made and energy is released. Energies to make and break these bonds are known. Using the bond energies of H-H 104 kcal/mole, O-O 119 kcal/mole, and H-O 111kcal/mole from Table 8, we can see how much energy is released when bonds are broken and formed.
BONDS BROKEN
BONDS FORMED
Bonds
# of bonds
Energy Required
Energy Released
H-H 2
208 kcal
H-O 4
444 kcal
O=O 1
119 kcal
Total
327 kcal required
444 kcal released

17. An energy diagram of the formation of water

18. Activation Energy
The energy needed to break the bonds apart is called the “activation energy”. It is the bump in the graph.
AE is the amount of kinetic energy required by the moving H2
and O2 molecules to rip them
apart and slam into each
other to create H2O.

19. Reaction can go in reverse!
When it looks like a reaction is done, it is only in equilibrium…some reactants making product AND some products are turning back into reactants..
2H2(g) + O2(g) H2O(l)

20. Rate of Reaction (Rxn)
How fast a reaction proceeds and which direction it favors (forward or reverse) depends on several factors:
Amount of reactants and products
More reactants will push forward 
More product will push reverse 
Temperature
Higher temp causes more movement of atoms
Direction of push depends if exothermic or endothermic
Pressure
Works like increasing amount of gases on either side
Presence of a catalyst
Lowers activation energy
2H2(g) + O2(g) H2O(l)

21. Homework
Write one paragraph (fve or more sentences) explaining an example or a metaphor for equilibrium. Specify the forward reaction and the backward reaction. Describe one thing you could do to change the system and what the effect would be. (eg...tight rope walker)
AND......
Sec 18.1 #1-5 p547

22. Th A N K S 90 124 7 19 16 Thorium Artificium Nitrogen Potassium
Sulpher