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Published byHoratio Roberts Modified over 9 years ago
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Noadswood Science, 2012
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To be able to measure the rate of reaction Tuesday, September 08, 2015
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Rate Different reactions can happen at different rates: - Reactions that happen slowly have a low rate of reaction Reactions that happen quickly have a high rate of reaction For example, the chemical weathering of rocks is a very slow reaction – it has a low rate of reaction, whilst explosions are very fast reactions – they have a high rate of reaction
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Rate Chemical reactions occur when particles of reactant collide with enough energy to react…
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Measuring How can you measure the rate of a reaction? Measure the rate at which a reactant is used up Measure the rate at which a product is formed The method chosen depends on the reaction being studied – sometimes it is easier to measure the change in the amount of a reactant that has been used up; sometimes it is easier to measure the change in the amount of product that has been produced… What can be measured?
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Measuring The measurement itself depends on the nature of the reactant or product… Mass of a substance (solid, liquid or gas) is measured with a balance The volume of a gas is usually measured with a gas syringe, or sometimes an upside down measuring cylinder or burette
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Equation The rate of reaction can be worked out simply, recording either the amount of reactant used / product formed and the time taken… Rate of reaction = amount of reactant used or amount of product formed time taken E.g. 24cm 3 hydrogen gas is produced in 2 minutes – what is the rate of reaction? Rate of reaction = 24 ÷ 2 Rate of reaction = 12cm 3 hydrogen gas produced per minute
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Experiment Complete the rate of reaction worksheet… CaCO 3 + 2HCl CaCl 2 H 2 O + CO 2
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Rates Of Reaction What factors effect the rate of reaction? Temperature Concentration of a dissolved reactant Pressure of a reacting gas Surface area of reactants Catalysts Chemical reactions occur when particles of reactant collide with enough energy to react – anything that increases the chance of effective collision increases the rate of reaction (e.g. surface area, temperature, pressure, using a catalyst etc…)
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Surface Area Look at the sugar cube and granulated sugar dissolving in the water – which will dissolve first? The granulated sugar dissolves much quicker than the sugar cube – this is due to the difference in surface area…
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Surface Area The reactions of solids can only take place at the surface of the solid – if the solid is broken into smaller pieces we get more area and a faster reaction… Molecules collide with surface of the substance Extra surface for molecule to collide with
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Surface Area If we grind up a solid to a powder we massively increase the surface area, massively increasing the rate of any reaction… Slow Fast
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Temperature How do the particles differ in cold water and boiling water? In boiling water the particles collide more often and with more force – they are moving quicker and with more energy…
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Temperature If the temperature is increased: The reactant particles move more quickly More particles have the activation energy or greater The particles collide more often, and more of the collisions result in a reaction The rate of reaction increases
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Concentration Concentration…
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Pressure Reactions involving gases are affected by the pressure of the gases present Increasing the pressure squeezes the gas molecules closer together (making them more concentrated) – pressure speeds up reactions Compress
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Catalysts For chemical reactions to occur: - Existing bonds have to begin breaking so that new ones can be formed The molecules have to collide in such a way that the reacting parts of the molecules are brought together Catalysts can help with either or both of these processes
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Catalysts Catalysts increase the rate of reaction without being used up – they do this by lowering the activation energy needed With a catalyst, more collisions result in a reaction, so the rate of reaction increases – different reactions need different catalysts Catalysts are important in industry because they reduce costs, e.g. Biological soap powder uses biological catalysts (enzymes) Enzymes in pineapple help cooked ham to be more tender Manufacture of fertiliser via the Haber Process involves use of an iron catalyst Catalytic converters in cars – the catalyst encourages decomposition of nitrogen oxide (poisonous) back into nitrogen and oxygen
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