Temperature effect on equilibrium Watch

smileyChris1993
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This is such a simple question that always manages to confuse me some how.

if you have a reaction at equilibrium and the forward reaction is endothermic then does increasing the temperature cause the equilibrium to move in the endothermic or exothermic direction?

this is one of those annoying questions I always seem to get wrong and just need someone to tell me so I can write it down and learn off by heart

thank you
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charco
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(Original post by smileyChris1993)
This is such a simple question that always manages to confuse me some how.

if you have a reaction at equilibrium and the forward reaction is endothermic then does increasing the temperature cause the equilibrium to move in the endothermic or exothermic direction?

this is one of those annoying questions I always seem to get wrong and just need someone to tell me so I can write it down and learn off by heart

thank you
Increasing temperature makes more energy available which can then be absorbed by the ENDOthermic change ...
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cerlohee
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I think it's better to understand it! If the forward reaction is endothermic, it's going to bring the temperature of the external surroundings down. If he temperature increases, in order to maintain the external conditions, the reaction is going to favour the reaction which reduces the temperature. In this case it's the forward reaction


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desslop
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(Original post by smileyChris1993)
This is such a simple question that always manages to confuse me some how.

if you have a reaction at equilibrium and the forward reaction is endothermic then does increasing the temperature cause the equilibrium to move in the endothermic or exothermic direction?

this is one of those annoying questions I always seem to get wrong and just need someone to tell me so I can write it down and learn off by heart

thank you
Think of it like this: Endothermic reactions cause a decrease in temperature whereas exothermic reactions cause an increase in temperature. Since any change in an equilibrium is reversed then increasing the temperature in a system means the reaction will try to decrease the temperature. Therefore increasing the temperature will favor the reaction that is endothermic.
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Pigster
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Think about your grandparents. If you think their house is cold and turn the heating up, they get annoyed and open a window. If you open a window on a hot day, they put on a jumper. Old people are happy at whatever temperature they are happy at.

Equilibria are happy too. If you make a change, they do whatever they can to oppose you. If you turn the heating up, they try to lower the temp and vice versa.

A nice absurd thought process involves increasing temp and an exothermic reaction. As you should know an exothermic reaction involves to release of heat, i.e. the system will get hot. If you turn the heat up and the reaction goes to the RHS, that's equivalent to putting on a jumper. And even my gran isn't that daft.
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smileyChris1993
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Cheers guys, that's helped alot. Especially the grandparents idea :P
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Borek
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Basically it is about applying Le Chatelier's principle.
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cuckoo99
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(Original post by Borek)
Basically it is about applying Le Chatelier's principle.
On the topic of Le Chateliers principle- why does increasing the total pressure of the system in equilibrium have no effect on Kc???

You are 1 of the chemistry guru's so i'm guessing you know the answer to this(my teacher doesn't "_").

Surely increasing pressure will cause the equilibrium to favor the reaction that produces the smallest number of moles of products.
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Borek
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Imagine having 1 mole of hydrogen in 1 L tank. That means concentration of 1 mol/L.

Imagine adding 2 moles of oxygen of to the same tank.

What is the hydrogen concentration now?
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cuckoo99
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(Original post by Borek)
Imagine having 1 mole of hydrogen in 1 L tank. That means concentration of 1 mol/L.

Imagine adding 2 moles of oxygen of the same tank.

What is the hydrogen concentration now?
Don't quite understand the wording of your question ?
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Borek
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Sorry, typo. TO the same tank.
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username1398367
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(Original post by Pigster)
Think about your grandparents. If you think their house is cold and turn the heating up, they get annoyed and open a window. If you open a window on a hot day, they put on a jumper. Old people are happy at whatever temperature they are happy at.

Equilibria are happy too. If you make a change, they do whatever they can to oppose you. If you turn the heating up, they try to lower the temp and vice versa.

A nice absurd thought process involves increasing temp and an exothermic reaction. As you should know an exothermic reaction involves to release of heat, i.e. the system will get hot. If you turn the heat up and the reaction goes to the RHS, that's equivalent to putting on a jumper. And even my gran isn't that daft.
analogies aside, why does this actually happen? an increase in temperature increases the kinetic energy of all molecules, so surely more molecules on both sides gain an energy greater than or equal to the activation energy...?
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Pigster
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Difficult to dumb down to A-level (assuming that's what you want), but the rate constants for the forward and backward reactions are affected by changes in T to differing amounts. i.e. for an exothermic reaction and an increase of T, the value of k in the backward reaction grows larger as a proportion of the increase of the value of k for the forward reaction.
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