H. Cordy-McKenna (Honywood School 2008) Understanding Rates of Reactions Use the green button to advance slides that contain animations

H. Cordy-McKenna (Honywood School 2008) What takes part in a reaction? Reactants – These are the chemicals that react together (on the left side of the chemical equation) Products – These are the chemicals that get made in the reaction (on the right side of the equation) Sometimes there may only be one reactant or one product. Can you think of an example?

H. Cordy-McKenna (Honywood School 2008) Copper + Oxygen  Copper oxide Copper oxide + Sulphuric acid  Copper sulphate + Water Reactants Product(s)

H. Cordy-McKenna (Honywood School 2008) Particles and Collisions Particles need to hit each other (collide) to react Anything that makes particles collide more often will speed up a reaction Faster collisions have more energy so they are more likely to react together

H. Cordy-McKenna (Honywood School 2008) Measuring the Rate of a Reaction You can measure how fast a reaction produces a gas

H. Cordy-McKenna (Honywood School 2008) Measuring the Rate of a Reaction You can measure how fast a reaction loses mass (when a gas is given off) Notice how both the reactions below lose the same mass by the end

H. Cordy-McKenna (Honywood School 2008) Measuring the Rate of a Reaction You can measure how long it takes for the reaction to take place.

H. Cordy-McKenna (Honywood School 2008) Low Temperature Particles move slower and have less kinetic energy They collide less frequently They collide with less energy The reaction is slower

H. Cordy-McKenna (Honywood School 2008) Higher Temperature Particles move faster and have more kinetic energy They collide more frequently They have more energy when they collide The reaction is faster

H. Cordy-McKenna (Honywood School 2008)

Concentration If a solution is more concentrated then there are more particles per volume (e.g. cm 3) than before (they are more crowded) Which of these is the most concentrated?

H. Cordy-McKenna (Honywood School 2008) Low Concentration Particles are not as crowded so they collide less frequently The reaction is slower

H. Cordy-McKenna (Honywood School 2008) High Concentration Particles are more crowded so they collide more frequently The reaction is faster

H. Cordy-McKenna (Honywood School 2008)

Surface Area Let’s say you have just killed George Bush and want to dissolve him in a vat of acid to get rid of the evidence. What could we do to his body to speed up the reaction before the police arrive?

H. Cordy-McKenna (Honywood School 2008) George’s Head On the next slide we will see arrows that show where the acid particles could collide with George’s head. The more chances for collisions then the faster his head will dissolve in the acid!

H. Cordy-McKenna (Honywood School 2008) LOADS more surface area for the acid particles to collide with

H. Cordy-McKenna (Honywood School 2008) Surface Area The greater the surface area the more collisions there will be The reaction happens faster

H. Cordy-McKenna (Honywood School 2008) Catalysts These speed up reactions without getting changed or used up How? They provide a surface where the reactants meet and react They also lower the activation energy needed for the reaction to happen

H. Cordy-McKenna (Honywood School 2008)

Catalyst Demo Click here for a great video of “Elephant’s Toothpaste”here The catalyst used causes hydrogen peroxide to break down and release oxygen Fairy Liquid traps the oxygen in bubbles with great results! The catalyst is NOT CHANGED or used up at the end, and could be re-used

H. Cordy-McKenna (Honywood School 2008) Rate of Reaction Graphs In exams they often show you a graph of a reaction It might show you how quickly a gas is made It might show you how quickly mass is lost The steeper the line the faster the rate of the reaction A reaction stops when no further change takes place (e.g. no more gas is made)

H. Cordy-McKenna (Honywood School 2008) A B C When is the reaction fastest? (Press a letter)

H. Cordy-McKenna (Honywood School 2008) A B C When is the reaction slowing down? (Press a letter)

H. Cordy-McKenna (Honywood School 2008) A B C When has the reaction stopped? (Press a letter)

H. Cordy-McKenna (Honywood School 2008) Use the pen to draw two more curves to show what would happen if this reaction happened at: (a) A higher temperature (b) A lower temperature Click here for the pen (and also to select “Arrow” when you have finished drawing

H. Cordy-McKenna (Honywood School 2008) Higher temperature Lower temperature Why does each reaction have the same end point in terms of gas produced? (Assume you are using the same concentrations and masses of reactants) Click the green button to move on…

H. Cordy-McKenna (Honywood School 2008) Summary Reactions need collisions between particles Rate of reaction is increased when particles collide more frequently Higher temperature, pressure and concentration increase the rate of collisions More surface area = More area for particles to collide with Catalysts speed up reactions without getting changed or used up

H. Cordy-McKenna (Honywood School 2008) Pressure in gases Increasing the pressure in a gas forces the particles close together They collide more often The reaction is faster