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12.4 How can we control the rate of a reaction?

12.4 How can we control the rate of a reaction?. Heolddu Comprehensive School. Rates of Reaction. Chemical reactions occur when different atoms or molecules collide:. For the reaction to happen the particles must have a certain amount of energy – this is called the ACTIVATION ENERGY.

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12.4 How can we control the rate of a reaction?

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  1. 12.4How can we control the rate of a reaction? Heolddu Comprehensive School

  2. Rates of Reaction Chemical reactions occur when different atoms or molecules collide: • For the reaction to happen the particles must have a certain amount of energy – this is called the ACTIVATION ENERGY. • The rate at which the reaction happens depends on four things: • The temperature of the reactants, • Their concentration • Their surface area • Whether or not a catalyst is used In exam questions on this stuff, talk about the particles involved in the reaction!!

  3. Measuring rate of reaction Two common ways: 1) Measure how fast the products are formed Rate of Reaction = Amount of product made or reactant used Time 2) Measure how fast the reactants are used up

  4. Rate of Reaction = Amount of product made or reactant used Time The units for rate will always be ‘x’/time. Where ‘x’ could be grams, cm3, ml etc. e.g. Rate = g/sec Rate = ml/min

  5. Rate of reaction graph Slower rate of reaction here due to reactants being used up Fast rate of reaction here Slower reaction Amount of product formed The Steeper the curve – the faster the rate of reaction Time

  6. Rate of reaction graph Slower rate of reaction here due to reactants being used up Fast rate of reaction here Slower reaction The rate of reaction can be worked out by dividing ‘y’ axis/’x’ axis, at any point on the graph Amount of product formed Time

  7. Using a Catalyst Hydrogen peroxide water + oxygen 2H2O2(aq) 2H2O(l) + O2(g) With a catalyst Without a catalyst A catalyst is a substance that increases the rate of reaction without being changed during the process. For example, consider hydrogen peroxide: Amount of oxygen formed Time

  8. Using Catalysts • Catalysts change the rate of chemical reactions but are not used up during the reaction. • Different reactions need different catalysts. • Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs. • Examples: • Iron in the Haber process • Nickel in making margarine

  9. Higher Tier • Concentrations of solutions are given in moles per cubic decimetre (mol/dm3). • Equal volumes of solutions of the same molar concentration contain the same number of moles of solute, i.e. the same number of particles. • Equal volumes of gases at the same temperature and pressure contain the same number of molecules.

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