Kinetics - without diagrams

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  • The minimum amount of energy that particles need in order to react is called the 'ACTIVATION ENERGY' (particles need energy to break bonds at the start of reactions)
    • Kinetics - (without energy  distribution and energy profile  diagrams)
      • Rate affecting factors
        • Increasing the temperature
        • Increasing the concentration of an aqueous reactant
        • Increasing the pressure of a gaseous reactant
        • Increasing the surface area of a solid reactant
        • The presence of light in certain reactionjs
        • The presence of a catalyst in certain reactions
      • Catalysts
        • A catalyst increases the rate of reactionfor very different reasons than increasing the concentration, surface area etc. CATALYSTS DO NOT ALTER THE ENERGY OF THE PARTICLES THEMSELVES SO....
          • A catalyst increases reaction rate by providing an alternative reaction pathway/mechanism, which lowers the activation energy.
        • For reactions in dynamic equilibrium
          • A + B , C + D
            • A catalyst would not alter the position of equilibrium. A catalyst would increase the rate of the forward reaction and the rate of the backward reaction by the same amount (catalysts increase the rate of ATTAINMENT of equilibrium.
        • They provide an alternative route/mechanism/pathway that has a LOWER ACTIVATION ENERGY.
          • They are unchanged at the end of the reaction.
            • For systems in EQUILIBRIUM - they increase the rate of the forwards and backwards reactions by the SAME AMOUNT. Thus the position of equilibrium DOES NOT CHANGE if a catalyst is used.
        • Classifying catalysts
          • Heterogeneous
            • Catalysts that are in a DIFFERENT PHASE to the reactants present (solids that catalyses gases)
              • The IRON catalyst in the HABER process for the production of ammonia.
                • The NICKEL catalyst in the hydrogenation of alkenes to form alkanes (used to convert oil into margarine):
                  • PLATINUM, PALLADIUM and RHODIUM catalysts used in catalytic convertors to convert harmful gases into less harmful gases.
          • Homogeneous
            • These are catalysts that are in the same phase as the reactants present.
              • The formation of an ester from an organic acid and an alcohol.
        • The future?
          • Many of today's catalysts require severe conditions of temperature and pressure
            • Enzymes (bio. cata.) are also important in certain industrial processes e.g. enzymes in yeast for the fermentation of sugar into alcohol.
              • Enzymes are particularly desirable as they often work under mild-conditions - e.g. low temperatures.
                • This is important as it lowers the temperature and pressure meaning less energy being used and therefore less CO2 being produced as a product.
      • Measuring reaction rates
        • Marble chips with acid....
          • CaCO3(s) + HCl(aq) ---. CaCl2 (aq) + H20(l) + CO2(G)
            • Method one - measuring the loss in mass.
              • Place reaction vessel on an electric balance. As gas is lost the mass will drop. Measuring mass at regular intervals allows us to work out mass lost at regular time intervals.
            • Method two - collecting and measuring the gas produced
              • Use a gas syringe to collect and measure the gas produced (CO2 with Carbonate, H2 with metals) or 2H20(l) (hydrogen peroxide) ----. 2H20 (l) + O2(g)
            • The rate of reaction - how could it be measured?
              • Colorimeter - measures the change in light intensity as the colour fades
        • Calculating rates
          • Units of rate for mass lost(g) in seconds (s)
            • g/s = g/s or gs-1
          • Units of rate for gas collected (Cm3) in seconds
            • cm3/s = cm3/s or cm3-1
          • Using a graph to calculate the initial rate
            • This is equal to t= 0(s)
              • Therefore you need to draw a tangent at t=0(s)
                • The tangent is extended, and a right angled triangle is drawn.
                  • The rate is found by....
                    • Delta g/cm3/moldm-3   divided by delta t.
    • The Chemical reaction will occi=ur when the reactant molecules COLLIDE with sufficient ENERGY. Such collisions are SUCCESSFUL COLLISIONS.
      • Therefore, if the number of collisions change, then the rate of reaction changes.


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