1. Topic 8
Reaction Rate

2. Chemical Reaction Rates
Chemical reactions can occur at different speeds.
Why does one reaction take longer than another?
Can you speed up or slow down reactions?

3. Four ways to Speed up Reactions
Increase Temperature
Increase Surface Area
Increase Concentration
Add a catalyst

4. Temperature Increasing the temperature increases the rate of reaction
Why? At higher temperatures, molecules move faster and collide more frequently.
Therefore, new substances can be formed more quickly.
Example: Cooking
The amount of chemical reactions in the liquid batter are increased with higher temperatures.
Example: Preserving Fruit
Fresh fruit and vegetables are often kept in the fridge to slow down the chemical reactions

5. Surface Area
Crushing materials increases the amount of surface area that is available to react.
A powder of a substance will react much more quickly than a block of the same substance.

6. Concentration
Increasing the amount of substance per unit of volume increases the amount of substance that is available to react.
If you are doing a lab with acid, a more concentrated acid will react faster than a dilute concentration.

7. Catalysts What is a catalyst? Natural catalysts are called enzymes
A substance that speeds up the rate of a reaction without being changed itself.
A catalyst increases the speed of the reaction – it doesn’t interfere with the products being created
Natural catalysts are called enzymes
Saliva is called salivary amylase – it breaks apart your food to aid in digestion
An enzyme in your tears attacks the cell wall of the bacteria to prevent an infection.

8. Inhibitors
Inhibitors are substances that slow down chemical reactions.
Examples:
Plants have inhibitors to stop germination until conditions are right
Foods and medicines have inhibitors in them to prevent decomposition
Hydrogen Peroxide has inhibitors in it to prevent its molecules from decomposing too quickly

9. Corrosion
Corrosion is the oxidation of metals or rocks in the presence of air and moisture.
The most common type of corrosion: Rust

10. Preventing Corrosion
Corroded materials lose their strength. Once materials lose the top layer, oxygen from the air can reach the inner layers.
Prevention?
Apply a thin coat of paint
Coat it with a thin layer of zinc – this process is called galvanization
Examples?
Galvanized nails so that job sites aren’t ruined
Chromium covered car parts to protect the lead
What is the electrochemical process to coat a metal with another type of metal?
Electroplating

11. Combustion
The highly exothermic combination of a substance with oxygen.
Every time something burns, it combines with oxygen from the air.
Even the food you eat is converted to energy by combining with the oxygen you breathe.

12. Products of Combustion
The products of burning a hydrocarbon (hydrogen and carbon) are always the same
Products: CO2(g) and H2O(g) and heat
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) + heat
C2H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) + heat