Chemistry - Rate and Extent of Change of Energy

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  • Rate and Extent of Change of Energy
    • The rate of a reaction is the  amount of product formed / reactant used, over time
      • You can show this with a graph, product formed on y and time on x
        • The steeper the line, the faster the rate of  reaction
          • When the line goes flat, the reaction has ended
        • Mean rate of whole reaction: overall change on the y, divided by total time
        • The rate of a specific point can calculated with the gradient of a tangent
      • The time can be measure by visual means
      • The produce  can be measure by a change in mass (gas given of)
        • It can also be measure by the volume of gas given of, via syringe
    • Collision Theory
      • The more collisions between reactants, the faster the reaction
      • Particles must collide with enough energy
    • Factors which affect the rate of reaction
      • Temperature: the faster moving particles will collide more, and with more energy
      • Concentration/pressure: there are more particles in a given area, so more collisions
      • Surface Area: for the same volume of solid, the reactants will have more room to work on, increasing collisions
      • Catalysts: they decrease activation energy by providing an alternate reaction pathway
    • Reversible Reactions
      • As the reactants react, their concentration falls, slowing t he forward reaction
        • As more products are formed and their concentrations rise the backward reaction will speed up
          • This continues until forward and backward reactions are going at the same rate, equilibrium
            • This only happens in a closed system
      • Equilibrium
        • This continues until forward and backward reactions are going at the same rate, equilibrium
          • This only happens in a closed system
        • If the equilibrium lies to the right, the concentration of the products is greater (and vice versa)
        • The reaction can be endothermic one way and exothermic the other
      • Le Chatelier's Principle
        • If you change the conditions, the system will try to counter act that change
          • If you add heat, the equilibrium will move in the endothermic direction to absorb heat making more endothermic products (and vice versa)
          • If you increase the pressure in gasses, the equilibrium will move to the direction where there is fewer moles (and vice versa)
          • If you increase the concentration of reactants, the system tries to decrease it by making more products ((and visa versa(and visa versa))

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