Topic 8 – Reaction RateTopic 8 – Reaction Rate

Science 9 - ChemistryScience 9 - Chemistry

Chemical Reactions involving oxygenChemical Reactions involving oxygen

1. COMBUSTION - 1. COMBUSTION - oxygenoxygen reacts with a reacts with a substance to from a new substance substance to from a new substance and give off energy and give off energy

Ex. Fire Ex. Fire

What products are produced in What products are produced in combustion?combustion?

CHCH4(g)4(g) + 2 O + 2 O2(g)2(g) CO CO2(g)2(g)+ 2 H+ 2 H22OO (g) (g)

Methane + oxygen Methane + oxygen carbon dioxide + water carbon dioxide + water

2. CORROSION – slow chemical change when oxygen in air reacts with metal Ex. Rust

4 Fe(s) + 3 O2(g) 2 Fe2O3(s)

Iron + oxygen iron oxide

How do we protect against rust?How do we protect against rust?

GalvanizingGalvanizing – Coating metals with thin – Coating metals with thin layers of zinclayers of zinc– Zinc takes longer to rust than most metals!Zinc takes longer to rust than most metals!

PaintingPainting Sacrificial metalSacrificial metal

PBS Nova – Smart BridgesPBS Nova – Smart Bridges

https://www.youtube.com/watch?v=8qcREJ2NsOQ

3. CELLULAR RESPIRATION – chemical reaction that takes place in your body cells.C6H12O6 + O2 CO2 + H2O + energy

Factors Affecting Rates of Factors Affecting Rates of Chemical ReactionsChemical Reactions

Many factors can affect chemical reactionsMany factors can affect chemical reactions One thing that must be controlled is the rate One thing that must be controlled is the rate

at which a reaction occurs (also known as at which a reaction occurs (also known as reaction rate (RR)).reaction rate (RR)).

REACTION RATE (RR) REACTION RATE (RR) – the speed at which – the speed at which reactants are converted to productsreactants are converted to products during a during a chemical reaction.chemical reaction.

1. Changing Temperature 1. Changing Temperature

• Temp = RR Temp = RR

• Temp = RRTemp = RR

2. Stirring the Reactants2. Stirring the Reactants

Adding movement Adding movement energy and speed of energy and speed of atoms / molecules = collisions between atoms / molecules = collisions between atoms = RRatoms = RR

3. Increasing Surface Area 3. Increasing Surface Area – The– The the the surface area the more chance the reaction surface area the more chance the reaction has to occur (smaller pieces) = RRhas to occur (smaller pieces) = RR

4. Catalysts4. Catalysts – A substance that RR without – A substance that RR without being changed itselfbeing changed itselfEx. Enzyme (natural catalyst) – made by living things Ex. Enzyme (natural catalyst) – made by living things

5. Changing Concentrations5. Changing Concentrations – number of particles – number of particles (atoms or molecules) per unit of volume changes RR(atoms or molecules) per unit of volume changes RR

– # of particles / unit of volume = RR# of particles / unit of volume = RR– # of particles / unit of volume = RR# of particles / unit of volume = RR

Ex. Ex. 18 mol/L H18 mol/L H22SOSO44 (aq) (aq)

vs.vs.

5 mol/L H5 mol/L H22SOSO44 (aq) (aq)

WHICH IS MORE CONCENTRATED?WHICH IS MORE CONCENTRATED?

WHICH WOULD REACT QUICKER?WHICH WOULD REACT QUICKER?