REACTION RATETopic 8

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?

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

Temperature Increasing the temperature increases the rate of

reactionWhy? 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 FruitFresh fruit and vegetables are often kept in the fridge to

slow down the chemical reactions

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.

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.

Catalysts What is a catalyst?

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 enzymesSaliva is called salivary amylase – it breaks apart

your food to aid in digestionAn enzyme in your tears attacks the cell wall of

the bacteria to prevent an infection.

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

Corrosion Corrosion is the oxidation of metals or

rocks in the presence of air and moisture.

The most common type of corrosion: Rust

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 paintCoat it with a thin layer of zinc – this process is called

galvanization Examples?

Galvanized nails so that job sites aren’t ruinedChromium covered car parts to protect the lead

What is the electrochemical process to coat a metal with another type of metal?Electroplating

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.

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) + heatC2H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) + heat