The document discusses chemical reactions and factors that affect their rates. It explains that reactions can be exothermic, releasing energy, or endothermic, absorbing energy. All reactions require a minimum amount of energy called the activation energy to initiate the rearrangement of reactants into products. The rate of reactions can be increased by raising the temperature, increasing the concentration or surface area of reactants, using catalysts to lower the activation energy, or through mechanical means like stirring. An experiment is described that shows reaction rates increase as particle size decreases due to greater surface area exposure.

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