Science 9 Unit B Matter and Chemical Change

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: 1. changing the temperature 2. stirring the reactants 3. changing the size (surface area) of reactants (example: grinding a reactant into a powder 4. 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 4 Fe(s) + 3 O 2(g) 2 Fe 2 O 3(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 combustion reaction of acetylene and oxygen is hot enough to melt metal 2 C 2 H 2(g) + 5 O 2(g) 4 CO 2(g) + 2 H 2 O + 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.