Chemical ReactionsTopic 7

Chemical Reaction happen all around us – even inside of us!

Chemical Reaction about to

take place…

Chemical Reactions Chemical Reactions (must know!)

• Two or more substances undergo a reorganization of atoms to form other substances.

Reactants (must know!)• The substances that go into a chemical reaction

Products (must know!)• The substances that are produced from a

chemical reactionReactant + Reactant Products

Reaction #

Reactants Products Word Equation

1 Hydrogen Peroxide + Heat

Water + Oxygen

Hydrogen Peroxide + Heat Water + Oxygen

2 Silver + Oxygen Silver oxide Silver + Oygen Silver oxide

3 Sodium + Bromine Sodium bromide Sodium + Bromine Sodium bromide

GIVE IT A TRY!

Chemical Reactions When iodine is placed on a potato - a

chemical reaction occurs and a blue-black colour is left. • Colour change indicates a chemical reaction

When two solutions are put together – they may form a precipitate (solid)• A precipitate and/or gas forming indicates a

chemical reaction• Example: Silver Nitrate with Sodium Hydroxide• Click here http://www.youtube.com/watch?v=SuoN0hQPeMw

Chemical Reactions When charcoal is burned, a

chemical reaction occurs.• Heat and light production

indicates a chemical reaction

When food spoils, its odour may change.• Odour change can indicate a

chemical reaction

Writing out Chemical Reactions1. Writing out word equations

2. Writing out chemical equations

Baking Soda and Vinegar! We know Baking soda and vinegar go

through a chemical reaction.

Word EquationBaking soda + Vinegar Sodium acetate + water + carbon dioxide

Chemical Equation

Try it out Situation: Burning Methane

Word EquationMethane + Oxygen Carbon Dioxide +

Water

Chemical EquationCH4(g) + O2(g) CO2(g) + H20(g)

Energy in Chemical Bonds Energy is stored in chemical bonds

To break bonds – energy is required

To form bonds – energy is released

Exothermic and Endothermic

Even though many reactions take and release energy, we look at whether it takes more or loses more.

Exothermic – Heat exits the chemical reaction

Endothermic – Heat enters the chemical reaction

Example Burning gas in the car

Word equation• Propane + oxygen carbon dioxide + water

Chemical equation• C3H8(g) + O2(g) CO2(g) + H2O(g) + energy (heat!)

Even though you need to put a little energy in to start the chemical reaction, the heat produced is enough to keep the reaction going and more.

Do You Recognize This Reaction?

Photosynthesis is a chemical reaction.

Is it exothermic or endothermic?

Do You Recognize This Reaction?

Endothermic:Why? Energy ENters the reactionWhen you eat sugars and starches, you are eating molecules formed by endothermic reactions. Your cells break down these molecules in an exothermic process that supplies the body with energy. This exothermic process is called cellular respiration.

Hot and Cold Packs Both hot and cold packs go through

chemical reactions Which goes through an endothermic

reaction? Which goes through an exothermic

reaction?

Hot and Cold Packs Both hot and cold packs go through

chemical reactions Which goes through an endothermic

reaction? Cold Packs Which goes through an exothermic

reaction? Hot packs