Collision theory

Starter – how fast does a reaction go? Some reactions are very slow Some proceed much more quickly For example…

Speed of reaction

Demonstration Reactions can be so fast that you don’t get burned… http://www.youtube.com/watch?v=1asvpQ9bcrY&feature=related

Rate of reaction How fast a reaction proceeds is just another way of describing the reaction “rate” Why would we want to control the rate of reaction? Because we want to make more products in less time using less energy What are the five factors that can affect rate of reaction? Can you guess? If not, look at the next slide for answers:

Collision theory In order to react, reactant particles must collide with each other When they collide they must be in the correct orientation AND must have sufficient energy. If we can make more collisions happen then the rate of reaction will increase (forming more products) How can we do this?

Factors which affect rate Temperature (increasing it would increase the speed at which the reactant molecules collide and so more products will form) Concentration (by adding more reactant molecules, more collisions will take place and so more products will form) Pressure (increasing it would make the container smaller, which will increase collisions and so more products will form) Surface area (making the reactant molecules smaller will increase the possibility of collisions and so more products will form) Catalysts (adding a catalyst -usually in powder form, to increase its surface area- will lower the energy barrier for the reaction and increase the rate, and so more products will form) http://www.youtube.com/watch?v=OttRV5ykP7A `

Speeding up reactions Anything that increases the chance of effective collision increases the rate (speed) of reaction. Factors include: Increased surface Area Increased concentration Increased temperature Use of a catalyst Increased pressure

Past paper question

Mark scheme