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    Equilibrium is the point where the rate of reaction going forward is the same a the rate of reaction backwards. What i want to know is why are the concentrations of reactions and products not equal
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    An equilibrium doesn’t mean that there are 2 moles of reactant and 2 moles of product. Just that both the forward and reverse reactions are moving at the same rate.
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    (Original post by HN786)
    Equilibrium is the point where the rate of reaction going forward is the same a the rate of reaction backwards. What i want to know is why are the concentrations of reactions and products not equal
    At equilibrium u wouldnt expect the amount of each reactant and product present to change provided all other physical quantities are kept the same, however u dont know how much of each reactant was in the start mixture, and the molar ratio of the reaction ;so u cannot say that there is equal amounts of reactants and products at equilibrium.
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    (Original post by HN786)
    Equilibrium is the point where the rate of reaction going forward is the same a the rate of reaction backwards. What i want to know is why are the concentrations of reactions and products not equal
    Each concentration is constant at equilibrium (because, as you rightly state, forward and backward reactions are happening at the same rate).

    The "position" of the equilibrium, (i.e. how far the forward reaction has progressed towards complete reaction) will not change at this point without making some change in conditions.
    However, this "position" of equilibrium could be more to the right, left or quite central relative to the equation. There is no reason for concentrations of reactants and products to be equal - in fact that is a very unlikely situation in real equilibria.
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    (Original post by TutorsChemistry)
    Each concentration is constant at equilibrium (because, as you rightly state, forward and backward reactions are happening at the same rate).

    The "position" of the equilibrium, (i.e. how far the forward reaction has progressed towards complete reaction) will not change at this point without making some change in conditions.
    However, this "position" of equilibrium could be more to the right, left or quite central relative to the equation. There is no reason for concentrations of reactants and products to be equal - in fact that is a very unlikely situation in real equilibria.
    So for the equilibrium N2 +3H2 -2NH3
    Im assuming because theres 4 moles on the reaction compared to two on products that at equilibrium there will be more reactant concentration
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    (Original post by HN786)
    So for the equilibrium N2 +3H2 -2NH3
    Im assuming because theres 4 moles on the reaction compared to two on products that at equilibrium there will be more reactant concentration
    Not necessarily. At this point you don't know how much "forward progress" the reaction has made when equilibrium is reached. We have no information whether, for example, 5% of the nitrogen and hydrogen have formed ammonia at that point, or 50% or 90% or any other amount of progress of the forward reaction has been made.

    At A level you will be introduced to the concept of equilibrium constant which will help you to predict how much "progress" has been made at equilibrium.

    For GCSE you should just be aware that the reaction is reversible, and that the only thing you can predict about concentrations at equilibrium is that they are now constant.
    Don't get tied up with the equilibrium giving equal amounts of reactants and products, because equilibrium doesn't work like that.
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    I teach this with two glass tubes: one with a large internal diameter, the other with a small diameter. It works best with two people.
    Start with two 100 cm3 measuring cylinders, both half full*.

    Place one tube in one cylinder (to the bottom), t'other in t'other.
    Place finger over hole at top.
    Pull out tube (now containing water) and put into t'other cylinder. Do likewise with other tube.
    Release water into tube.
    Return your tube to the starting cylinder.
    Repeat loads of times.

    Eventually, the levels of the water stay constant (allowing for occasional spillages).
    The volume of water being transferred between the two tubes is constant, i.e. the rate of water transfer is constant, but the quantities of water in the two cylinders is not, i.e. the concentrations of the reactants and products.

    Teachers: feel free to nick this. After all, I did off someone else.

    *Also, starting with different amounts, e.g. all the water in one, has no effect on the final outcome.
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    (Original post by Pigster)

    Teachers: feel free to nick this. After all, I did of someone else.
    Keeping to the water theme, I use this:

    Le Chatelier's buckets
 
 
 
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