topic 8. chemical reaction rates chemical reactions can occur at different speeds. why does one...
TRANSCRIPT
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 rightFoods and medicines have inhibitors in
them to prevent decompositionHydrogen 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) + heat
C2H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) + heat