AS level equilibrium - what is this concept?

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#1
Ok so I know about le Chatelier, but I'm puzzled... what actually is EQUILIBRIUM? I read that the rate of reaction is the same both backwards and forwards reaction - this is known as dynamic equilibrium.
BUT then it talks about "shifting equilibria" - like what is this concept? From what I understand, equilibrium is a state of balance between a constant reaction, so if an equilibria were to shift, what does this represent??? E.g. if equilibria were to shift towards NH3, does that mean more molecules of NH3 are being produced in order to match the no. of molecules of reactants (N2 and H2)?

Is whatever side the equilibrium is on, the side with more molecules?

Sorry this question doesn't seem to make sense, but "shifting equilibria" is a bit of a weird concept for me right now. Why do we need to know it shifts, when we can just say there is an equilibrium? Does shifting mean that part of a reaction has changed to suit a change in energy of the closed system?
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5 years ago
#2
This is exactly what I thought when I was learning this - no one ever explained it properly! I think I have a better idea now...

When a change occurs in a system, the system acts the counteract that change - it does this by shifting the equilibrium position.

For example, if a reactant's concentration in a system is increased, the system will move to the right in order to decrease the concentration of that reactant. By that, I mean that the equilibrium position moves to the right.

HOWEVER, changing the concentrations of reactants and products has no effect on the rate constants of the forward or reverse reactions. Therefore it has no effect on the equilibrium constant.

Equilibrium constant (this is the value of Kc) is different from equilibrium position. I hope this helps, I can give another example if you want?
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#3
(Original post by h8skoooooool)
This is exactly what I thought when I was learning this - no one ever explained it properly! I think I have a better idea now...

When a change occurs in a system, the system acts the counteract that change - it does this by shifting the equilibrium position.

For example, if a reactant's concentration in a system is increased, the system will move to the right in order to decrease the concentration of that reactant. By that, I mean that the equilibrium position moves to the right.

HOWEVER, changing the concentrations of reactants and products has no effect on the rate constants of the forward or reverse reactions. Therefore it has no effect on the equilibrium constant.

Equilibrium constant (this is the value of Kc) is different from equilibrium position. I hope this helps, I can give another example if you want?
So from what I have understood, equilibrium is the point where reactants to products are equal.

So you saying that when the balance has been disturbed i.e. increase in reactant concentration, this equilibrium point will shift to the right? But WHY to the right and not to the left? So the core question is, "what is equilibrium actually representing?"
Btw thank you for your time replying 0
5 years ago
#4
(Original post by simply_a_ Δ)
So from what I have understood, equilibrium is the point where reactants to products are equal.

So you saying that when the balance has been disturbed i.e. increase in reactant concentration, this equilibrium point will shift to the right? But WHY to the right and not to the left? So the core question is, "what is equilibrium actually representing?"
Btw thank you for your time replying it's shifting to the right to counteract the increase in the concentration of the reactant. The reactant is used up if we go rightwards, correct? So that's how the equilibrium will behave in order to return back to how it was before.
0
5 years ago
#5
From what I have learnt,
at equilibrium the concentrations of reactants and products remain constant.
For this to happen the rates of the forward and backward reactions have to proceed at the same rates.
The concentrations of reactants and products are not the same.
Every chemical reaction will have a certain ratio at which equilibrium will occur.
Equilibrium tends to shift in order to minimise the effect of the change that is acted upon the system.

I like to think of it as running up an escalator. When you are running but you aren't moving any further up the escalator, that is when you are at equilibrium. If you speed up (change acts upon system) the escalator, then you have to run faster in order to not go further down the escalator and to maintain your position. This position is your equilibrium.

I don't whether that is correct but that is my thinking anyway.
0
5 years ago
#6
(Original post by simply_a_ Δ)
So from what I have understood, equilibrium is the point where reactants to products are equal.

So you saying that when the balance has been disturbed i.e. increase in reactant concentration, this equilibrium point will shift to the right? But WHY to the right and not to the left? So the core question is, "what is equilibrium actually representing?"
Btw thank you for your time replying A reaction exists at equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction, so the concentrations of the products and reactants stay constant over time.

The equilibrium concentration position of a reaction is "to the right" if, at equilibrium, lots of the product is formed. The equilibrium position is said to be "to the left" if hardly any product is formed from the reactants.

The position of equilibrium can shift in order to counteract any changes in concentration, temperature or gas pressure, so that the rates of the forward and reverse are equal again.
1
#7
(Original post by High Stakes)
it's shifting to the right to counteract the increase in the concentration of the reactant. The reactant is used up if we go rightwards, correct? So that's how the equilibrium will behave in order to return back to how it was before.
Ohh, so would it be correct to think of equilibrium as the "direction the reaction favours" e.g. as you pointed out that equilibrium shifts to the right meaning that the reaction is going rightwards IN ORDER to create more products to MAINTAIN EQUILIBRIUM?
0
5 years ago
#8
(Original post by simply_a_ Δ)
Ok so I know about le Chatelier, but I'm puzzled... what actually is EQUILIBRIUM? I read that the rate of reaction is the same both backwards and forwards reaction - this is known as dynamic equilibrium.
BUT then it talks about "shifting equilibria" - like what is this concept? From what I understand, equilibrium is a state of balance between a constant reaction, so if an equilibria were to shift, what does this represent??? E.g. if equilibria were to shift towards NH3, does that mean more molecules of NH3 are being produced in order to match the no. of molecules of reactants (N2 and H2)?

Is whatever side the equilibrium is on, the side with more molecules?

Sorry this question doesn't seem to make sense, but "shifting equilibria" is a bit of a weird concept for me right now. Why do we need to know it shifts, when we can just say there is an equilibrium? Does shifting mean that part of a reaction has changed to suit a change in energy of the closed system?
Le Chatelier's principle states that if a closed system is disturbed i.e a factor is changed, the equilibrium will shift to oppose the change.
When there is a 'dynamic equilibrium' it means that the rates of the forwards and backwards reaction are equal. 'Dynamic' implies that the reaction is still ongoing and not static, albeit at the same rates.
In a reversible reaction, the reactants react to form products and the products react to form reactants. Initially the forward reaction, which is the reaction which involves reactants reacting to form products, is a lot faster than the backwards reaction. This is because there are a lot of reactant particles, which means that the frequency and likelihood of successful collisions is high and so the rate of the forward reaction is fast.
In the reaction which involves forming NH3, N2 + 3H2 > 2NH3 (Note there should a reversible sign), we need to know the effect of changing a factor e.g. temperature, if the forward reaction is exothermic than decreasing the temperature will favour the forward reaction (i.e the equilibrium will shift to the right) i.e. more NH3 will be produced. This is because again, according to Le Chateliers principle, the decrease in temperature (change) will be opposed i.e. reversed. Manufacturers of NH3 are particularly interested in the rates of reaction etc and how the yield of NH3 can be increased.

Let me know if you have any further questions.
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