Science 9 Unit B: Matter and Chemical Change Lesson 2-4: Types of Reactions (we saw yesterday) and Factors affecting rates of reaction

Reaction Rate a measure of how fast a reaction occurs can be measured by how quickly a reactant disappears or product appears

Changing Reaction Rate can be sped up or slowed down by: changing the temperature stirring the reactants changing the size (surface area) of reactants (example: grinding a reactant into a powder increase the concentration of a reactant (this increases the number of particles per unit volume)

Catalyst a substance that speeds up the rate of reaction without being changed itself does not affect the amount of product increases only the speed of the reaction

Enzymes are natural catalysts made by living things. almost all chemical reactions in the human body are catalyzed by enzymes when chewing carbohydrates, salivary amylase (which is an enzyme) breaks down starches into smaller molecules one of the most important group of enzymes are the proteases, which break down proteins proteases are used in meat tenderizers and contact lens cleaning solutions Video

Inhibitor a substance that slows down chemical reactions inhibitors are found naturally in seeds to prevent germination until conditions are just right an inhibitor is added to hydrogen peroxide to prevent its molecules from decomposing too quickly

Corrosion is the oxidation of metals or rocks in the presence of air (oxygen) and moisture Rust (iron oxide) is an example of corrosion 4Fe(s) + 3O2(g)  2Fe2O3(s) (iron) (oxygen) (iron oxide) corroded materials lose their strength corrosion occurs on the metal surfaces and at points of strain, eventually making it all the way through

corrosion can be prevented: applying a thin coat of paint galvanization, the process of coating metals with a thin layer of zinc (example – galvanized nails) coating car bumpers with a thin layer of chromium to protect the iron from corroding aluminum oxidize quickly forming aluminum oxide which seals the surface and stops corroding as a result, aluminum cans will take over 400 years to degrade

Electroplating the process of covering a metal with another metal by using electrolysis is called electroplating

Combustion combustion (requires heat, oxygen and fuel) is a highly exothermic combination of a substance with oxygen

Combustion examples include a fireplace, a gas barbecue, or the furnace in your home also takes place inside the internal combustion engine of a car gasoline combines with oxygen to release energy to make the car move

Products of Combustion food you eat is converted to energy by combining with the oxygen that you breathe the combustion reaction of acetylene and oxygen is hot enough to melt metal 2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O + energy (acetylene) + (oxygen)  (carbon dioxide) + (water vapour) + (heat) (Acetylene torch welding)

Fire Triangle

Today: You’ll be investigation factors that affect rates of reaction Complete Lab 2-3: Investigating Conditions that affect rate of reaction.