1/3/2012 Chemical and physical changes Write the date and title in your books and unscramble the learning objective. LO: ot wonk eht ecnereffid neewteb lacisyhp segnahc dna lacimehc snoitcaer.

Learning objective: To Know the difference between a chemical reaction and a physical change Success Criteria Level 6 – Explains observations Level 5 – Observes and records chemical and physical changes Level 4 – Describes the differences between reactants and products Level 3 – Can recall the words reactants and products Chemical and physical changes

Physical changes and chemical reactions Physical change: a change that occurs that does not change the identity of the substance. Chemical reaction: a change that occurs causing the identity of the substance to change, so reactants form products.

How do we know a chemical reaction has happened? Indicators of a chemical change: Evolution of light Evolution of heat Evolution of a gas Color change Formation of a precipitate

Substances ObservationsChemical reaction or physical change? Ice cube Water in kettle Candle wax Bunsen burner + wood splint paper Bicarbonate of soda + vinegar Salt + water Two coloured solutions

Chemical reactions Physical changes New substances are formed Changes are usually permanent ie Irreversible No new substances are formed Changes are usually NOT permanent ie Reversible Chemical reactions Physical changes V Summary of differences between them

Chemical Reactions – not easy to reverse During chemical changes (reactions) different atoms become bonded. Chemical bonds are not easy to break. Because of this chemical changes are usually difficult to reverse. (It is difficult to change products back into reactants.) E.g. We cannot “un-burn” magnesium. Note: although many reactions give out heat once started they often need energy to get them going. oxygen O O magnesium oxide Mg O O magnesium 

Description of a chemical reaction. Using all of the key words in the box below, write a description of a chemical reaction. Once you have finished try and think what we call total mass of reactants = total mass of products. Products reactants irreversible Bonds colour change bubbles Observation energy

Learning objective: To Know the difference between a chemical reaction and a physical change Success Criteria Level 6 – Explains observations Level 5 – Observes and records chemical and physical changes Level 4 – Describes the differences between reactants and products Level 3 – Can recall the words reactants and products Chemical and physical changes

Adding acid to alkali FireworksDriving a car Ice cream melting Boiling the kettlefrying an egg Burning a candle Melting candle wax Dissolving sugar in tea Lighting a match Making ice cubes Ironing clothes PrintingBaking a cake Launching a space rocket which of these are chemical reactions? xx x x xx x