4.1: How fast?

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  • Created by: Jordan64
  • Created on: 23-04-16 12:19
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  • C2.4: Rates and energy
    • 4.1: How fast?
    • 4.2: Collision theory and surface area
    • 4.3: The effect of temperature
      • Reactions happen more quickly as the temperature increases
        • This means they collide more often, which increases the rate of reaction
          • As well as colliding more frequently, they collide with more energy, which also increases the rate of reaction
            • Reactions happen more quickly as the temperature increases
              • This means they collide more often, which increases the rate of reaction
                • As well as colliding more frequently, they collide with more energy, which also increases the rate of reaction
                • Increasing the temperature increases the rate of reaction because particles collide more frequently and more energetically
                • A small change in temperature has a large effect on reaction rates: a temperature rise of 10 degrees will roughly double reactions so they go twice as fast.
                  • Increasing the temperature increases the rate of reaction because particles collide more frequently and more energetically
          • A small change in temperature has a large effect on reaction rates: a temperature rise of 10 degrees will roughly double reactions so they go twice as fast.
        • 4.6: Catalysts in action
          • Catalysts are used in industry to increase the rate of reactions and reduce energy costs.
            • If fossil fuels are burned to provide energy for industrial reactions, using catalysts will help to conserve resources and reduce pollution.
            • Some catalysts are expensive, but they can be economical because they do not need replacing very often
            • This helps to reduce costs and reduce impacts on the environment.
            • Many of the catalysts used in industry are traditional catalysts. They are often transition metals or their compounds
              • Some of these metals and their compounds are toxic and may cause harm if they get into the environment
              • They are used in many industrial processes because they can reudce the energy and the time needed for reactions.
              • Modern catalysts are being developed in industry which result in less waste and are safer for the environment
                • Finding new and better catalysts is a major area of research for the chemical industry.
                • Nanoparticles offer exciting possibilities for developing new, highly efficient catalysts.
                  • If this can replace more traditional catalysts, they will reduce energy costs even further.
                • Enzymes are biological catalysts that work at ordinary temperatures.
                  • If this can replace more traditional catalysts, they will reduce energy costs even further.
        • 4.5: The effect of catalysts
          • A catalyst speeds up the rate of reaction
            • They speed up the reactions and therefore lower the axctivation energy of the reaction so that more of the collisions result in a reaction
        • 4.7: Exothermic and endothermic reactions
          • Energy may be transferred to or from the reacting substances in a reaction
            • When chemical reactions take place energy is transferred as bonds are broken and made
            • A reaction in which energy is transferred from the reacting substances to their surroundings is called an exothermic reaction.
              • The energy transferred often heats up the surroundings and so the temperature increases
                • Exothermic reactions include:
                  • Combustion, such as burning fuels
                  • Neutralization reactions involving acids and bases
            • A reaction in which energy is transferred to the reacting substances from their surroundings is called an endothermic reaction
              • Some cause a decrease in temperature and others require a supply of energy.
                • When some solid compounds are mixed with water, the temperature decreases because endothermic changes happen as they dissolve
                  • Thermal decomposition reactions need to be heated continuously to keep the reaction going
                    • Some cause a decrease in temperature and others require a supply of energy.
                      • When some solid compounds are mixed with water, the temperature decreases because endothermic changes happen as they dissolve
                        • Thermal decomposition reactions need to be heated continuously to keep the reaction going
          • 4.9: Using energy transfers from reactions
            • Endothermic reactions can be used to cool things
              • Endothermic  changes can be used in instant cold packs for sports injuries
                • Some chemical cold packs contain ammonium nitrate and water that are kept separated.
                  • When mixed together, the ammonium nitrate dissolves and takes in energy from the surroundings - this can be used on sports injuries, or to cool drinks.
                    • The reaction is reversible, but not in the pack, so this type of pack can only be used once.
            • Exothermic changes can be used to heat things
              • An example is hand-warmers and self-heating cans
                • Some hand-warmers use a reversible reaction such as the crystalisation of a salt - once used, the pack can be heated in boiling water to re-dissolve the salt - this can be re-used many times
                • Some hand warmers can't be used again because they use reactions such as the oxidation of iron or the reaction of calcium oxide with water - both non-reversible
        • An average rate can also be found by measuring the time it takes for a certain amount of solid in the solution.
          • If a gas is given off in the reaction, it's average rate can be found by measuring the time taken to collect a certain amount of gas
        • The gradient or slope of the line on a graph of amount of reactant or product against time tells ups the rate of reaction at that time.
          • We can collect the data for the graph by measuring the mass of gas released or the volume of gas produced at intervals of time
            • Other possible ways include measuring changes in colour, concentration or pH of a reaction mixture, over time.
          • We can find the rate of a chemical reaction by measuring the amount of reactants used up over time or by measuring the amount of products made over time.
            • An average rate can also be found by measuring the time it takes for a certain amount of solid in the solution.
              • If a gas is given off in the reaction, it's average rate can be found by measuring the time taken to collect a certain amount of gas
          • Steeper gradient = faster reaction
        • Factors that increase the chance of collisions, or the energy of the particles will increase the rate of reaction.
          • Factors that will increase the rate of reaction include:
            • Temperature
            • Concentration of solutions
            • Pressure of gases
            • Surface area of solids
            • Using a catalyst
          • The minimum amount of energy that particles must have in order to react is called the activation energy
            • Collision theory states that reactions can ONLY happen if particles collide
              • 4.2: Collision theory and surface area
        • The rate of a chemical reaction also increases if the surface area of any solid reactants is increased
          • This increases the frequency of collisions between reacting particles
          • Factors that increase the chance of collisions, or the energy of the particles will increase the rate of reaction.
            • Factors that will increase the rate of reaction include:
              • Temperature
              • Concentration of solutions
              • Pressure of gases
              • Surface area of solids
              • Using a catalyst
            • The minimum amount of energy that particles must have in order to react is called the activation energy
              • Collision theory states that reactions can ONLY happen if particles collide
          • Increasing the pressure of a gas puts more molecules into the same volume, ad so they collide more frequently.
            • This therefore increases the rate of reactions that have gases as reactants

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