utv
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can anyone help me understand this. le chatliers principle is if you change the conditions in a system AT EQUILIBRIUM . equilibrium will shift to counteract the change


so when making Ethanol

the system is at equilibrium. the concentration of ethanol andwater and ethene are the same. so why would we use a high temperature to increase the rate when it would decrease the yield when we can use the ethanol we have already at equilibrium initially?
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username1445490
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Just because it is at equilibrium does not mean the concentrations are all the same but they do not change.
If you have an equilibrium which lies well to the right you will get a high yield but it may be very slow. This is not good if you are trying to make a lot of something. So we heat it to increase the rate and make the product quicker but if the forward reaction is exothermic the equilibrium will shift to the left and reduce the yield so we have to have a compromise. The temperature has to be high enough to give a good rate but not so high to overally affect the yield.
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utv
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but doesn't the initial solution have to be at equilibrium before? as le chatliers principle says for a system at equilibrium. so if already at equilibrium there's already a higher concentration of ethanol then there will be if we increase the temperature. surley rate of reactions don't matter if we already have a higher yield of the product
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username1445490
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(Original post by utv)
but doesn't the initial solution have to be at equilibrium before? as le chatliers principle says for a system at equilibrium. so if already at equilibrium there's already a higher concentration of ethanol then there will be if we increase the temperature. surley rate of reactions don't matter if we already have a higher yield of the product
At equilibrium there isn't a high yield of ethanol. Only about 5%. The equilibrium lies to the left.
Heating it up pushes it further to the left but increases the rate. The overall yield is increased to around 95% by removing the ethanol and recycling the other reactants.

See https://www.chemguide.co.uk/physical...a/ethanol.html
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