Chemistry | The Rate and Extent of Chemical Change.

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  • Created on: 05-09-19 17:45
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  • The Rate and Extent of Chemical Change.
    • Rates of Reaction
      • The rate of a chemical reaction is how fast the reactants turn into products.
      • To find out the speed of a reaction you record either the amount of products formed or reactants used up over time.
      • The steeper the line on a graph, the faster the rate of reaction.
      • Flat lines show a reaction has ended.
    • Factors Affecting Rates of Reaction
      • Particles must collide with enough energy in order to react
      • Rates of a chemical reaction depends on:
        • The collision frequency of reacting particles, the more collisions there are the faster the reaction is.
        • The energy transferred during a collision.
      • The minimum amount of energy the prticles need to react is the activation energy.
      • What does the rate of reaction depends on?
        • Temperature
        • Concentration of a solution or the pressure of gas.
        • Surface Area
        • Presence of a catalyst.
          • a catalyst is something that speeds up a reaction without being used up in the reaction.
      • More collisions increases the rate of reaction.
    • Measuring Rates of Reaction
      • The rate of reaction can be obsered either by how fast the reactants are being used up or how fast the products are formed.
      • Rate of reaction = amount of reactants used or products formed (gas - cm^3 or solid - grams) / time (seconds).
      • Precipitation & Colour Change
        • You record how long it takes until you can no longer see the marked paper through the beaker.
      • Change in Mass
        • Record the decrease of mass of the beaker every couple of seconds as soon as the mass starts to drop.
      • The Volume of Gas Given Off
        • Use a gas syringe to record the amount of gas getting out of the beaker.
    • Reverible Reactions
      • Reversible reactions are reactions that can work both forwards and backwards.
      • Reversible reactions will reach equilibrium.
      • As reactants react, their concentration falls - so the forward reaction will slow down. Yet as more products are made, their concentration rises and the backward reation will speed up.
      • When the forward reaction goes at the same rate as the backward reaction - thats when it reaches eqilibrium.
        • Equilibrium means that both reactions are happening but theres no overall effect. It can only be reached if the reversible reaction takes place in a closed system. It means that none of the reactants or products can escape and nothing else can get in.
      • The position of equilibrium can either be on the left or the right side.
      • When equilibrium is on the right, the concentration of products is higher than reactants. If it is on the left, the concentration of the reactants is higher than the products.
      • The position of equilibrium depends on: the temp, the pressure and the concentrationof the reactants and the products.
      • Reversible reactions can be endothermic and exothermic.
    • Le Chatelier's Principle
      • Its the idea that if you change the conditions of a reversible reaction the system will try to conteract the change.
      • Temperature
        • All reactions are exothermic in 1 direction and endothermic in another.
        • If the temp has decreased, the equilibrium will move in the exothermic direction. Meaning that there will be more products for the exothermic reaction than endothermic. And vice versa.
      • Pressure
        • Changing pressure only affeects an equilibrium involving gases.
        • If you increase the pressure, the equiliibrium moves in the direction where there are more molecules of gas. And vice versa.
      • Concentration
        • If you change the concentration of either the reactants or products, the system won't be in equilibrium any longer. The system would respond by bringing itself back to equilibrium.
        • If you try to increase the concentration of the reactants the system tries to decrease it by making more products. And vice versa.
    • Practice Q's


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