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Speed of Reactions

Speed of Reactions. We can increase or decrease the rate( speed) of a reaction. Factors that affect rate Temperature Concentration of reactants Surface area of reactants Using a catalyst. Monitoring Rate.

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Speed of Reactions

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  1. Speed of Reactions • We can increase or decrease the rate( speed) of a reaction. • Factors that affect rate • Temperature • Concentration of reactants • Surface area of reactants • Using a catalyst.

  2. Monitoring Rate • We can work out how fast a reaction is by measuring the amount by which the reactants have been used up or how much product has been made in a certain amount of time. • Example • Hydrochloric Acid +Chalk —> Salt + Carbon dioxide + Water • We can monitor the reaction by: • The volume of gas produced in a certain time or the decrease in mass of the reactants in a certain time.

  3. What happens to the particles in a reaction? • For a chemical reaction to take place the reactant particles must collide with each other. • The more times they collide the greater chance they will react together. • To increase the rate we must try to increase the chance of collisions between reactant particles.

  4. Particle Size • We can increase the rate if we make the particles smaller. • This gives a bigger Surface Area for the reactant particle to collide with one another. • Think! – A dice has 6 sides – if we half the dice we now have 12 sides – if we keep halving we increase the number of sides – we are increasing the Surface Area. • Example – Cooking – Small potatoes will cook faster than large potatoes!

  5. Temperature • When we increase the temperature the particles move about more. • If they are moving – the greater chance they will collide with each other. • The greater chance they will react. • Example • The exhaust pipe in a car rots quicker than the rest – it is hotter here – faster reaction. • Food goes off less quickly in a fridge – lower temperature – slower reaction.

  6. Concentration • The greater the concentration the faster the reaction. • The greater the concentration- the more particles present – the greater chance they will collide and react together. • THINK! • If you have two people running around a room they may bump in to one another – if you have 100 people running around the same room there is a much greater chance they will bump!

  7. Catalysts • Catalyst are substances we add to a reaction to make it go faster. • Catalysts are not used up in the reaction and so can be used again. • They cut down the costs because they allow the reactions to happen at lower temperatures. • Catalysts are usually very specific and will speed up only certain reactions.

  8. Enzymes • Enzymes are “Biological Catalysts” • They speed up chemical reactions in living things. • Example • Amylase is in Saliva. It speeds up the breakdown of starch to sugar. It will not speed up any other reaction ( e.g. locks can only be opened by the correct Key!) • Enzymes work at Optimum conditions. • They will only work at the correct temperature and pH.

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