1. Energy in Chemical Reactions
Most Chemical reactions will either give off
energy, or take in some energy.

2. Exothermic Reactions:
• A chemical reaction in which
energy (usually heat) is released.
•Will feel warm to you
Endothermic Reactions:
• A chemical reaction in which energy
is absorbed or added ( usually heat
or electricity).
•It may feel cold.
REVIEW!!

3. Activation energy:
• The energy needed by reactants to start the
reactions
• The molecule then rearranges to form the
products of the reaction.
• Different reactions have a greater or lesser
activation energy, but all reactions have this
“energy hill”.

4. Heat, light, …
something

5. Heat, electricity,
…something, …
otherwise the
reaction won’t
take place.

6. Reaction Rate Experiment
1-put 150ml of water in a beaker
2-Time how long it takes for each tablet to
dissolve.
3- Make a conclusion based on your data. How
does the particle size affect the reaction rate?
Tablet Type Time to dissolve (sec)
Whole
Small pieces
Crushed powder

7. Reaction Rate Conclusions
 The smaller the particle size, the
_____________ faster/slower it will be
dissolved.
 The warmer the water, the
____________faster/slower it will be
dissolved.
 The more you stir it, the _____________
faster/slower it will dissolve.

8. Collision Theory:
• … relates molecular collisions to reaction
rates.
• Four factors involved:
• Concentration ( percentage of reactant particles)
• Temperature (most reactions progress faster at
higher temps)
• Surface area ( the more you have the greater the
reaction rate)
•Catalyst or inhibitor

9. Catalyst:
• A substance that increases the rate of a
chemical reaction without changing itself.
• Lowers the activation energy.
• Enzymes in your gut.
Inhibitor:
• substances that slow down a
reaction.
• Food preservatives