rates of reaction

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  • Created by: geogt002
  • Created on: 08-06-16 13:42
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  • rates of reaction
    • can be measured by the rate at which reactant is used up or the rate n which a product is formed.
    • the temp, concentration, pressure of reacting gases, surface area of reacting solids and the use of catalyst are all factors that affect the rate of reaction.
    • chemical reactions can only happen if reactant particles collide with enough energy. the more frequently particles collide, the greater the proposition of collisions with enough energy. the greater the rate of reaction.
    • measuring rates
      • different reactions happen at different rates. slow rates of reaction have a low rate of reaction. quick reaction have a high rate of reaction.
      • the chemical weathering of rocks has a very SLOW reaction, therefore a very LOW rate of reaction.
      • explosions are very fast reactions they have a high rate of reaction.
    • reactants and products.
      • ways to measure.
      • mesure the rate in hwich a reactant is used up. a reactants are a substance that is present at the start of reaction.
      • measure the rate in which a product is formed. ( a substance formed in a chemical reaction.)
      • the method chosen depends on the reaction being studied.
    • the measurement itself depends on the nature of the reactant or product. the mass of a substance is measured with a balance. the volume of gas is usually measured with a syringe, cylinder or burette.
    • it is usual to record the mass or total volume at regular intervals and plot a graph. the readings go on a vertical axis and time goes on the horizontal. the rate of reaction equals the amount or product formed divided by the time taken.
    • how to increase the rate of reaction?
      • temp increased, concentration of reactant increases, pressure of reactant gas increases, solid reactants are broken into smaller pieces.or a catalyst is used.
      • the steeper the line the greater the rate of reaction.reactions are usually fastest at the beginning, when the concentration of reactants is greatest. when the line become horizontal the reaction has stopped.
    • collisions
      • for a chemical reaction to occur the reactant particles must collide. collisions with to little energy do not produce a reaction. minimum energy needed fore particles to react is called activation energy.
      • if the concentration of a dissolved reactant is increased or the pressure of reactant gas is increased there are more reactant particles in the same volume. there is also greater chance of them colliding and the rate of reaction increases.
      • changing particle size...if a solid reactant is broken into small pices and ground into powder. its surface area is increased, more particles are exosed to the other reactant, the is a reater chnace of the particles coliding and the rate of reaction increases.
      • chnaging the temp...if it is increased the particles move more quickly, kore particles have the activation energy, the particles collide more often and more of the collision results in a reaction, the rate of reaction also increases.
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