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Chemistry: Post your doubts here!

Xylferion

Xylferion

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Midnight dream said:
sorry but i still dont understand it..
Look when we raise the temp. both forward and the backward reactions increase and if the forward reaction is exothermic then the equilibrium shifts to the left.To counter it the reaction moves in the left side. And Kc is affected.
When we raise pressure, both forward and backward reactions increase and if more moles on the right hand side then equilibrium shifts to the right.But kc not affected.
Why?
Click to expand...

I found this explanation on another forum and it explained it very well.

"If you consider a gaseous system at equilibrium then the total number of moles is constant, the temperature is constant and so according to the gas laws if you wish to increase the pressure you MUST change the volume (decreasing it).
Concentration is given by moles/volume so you therefore change (increase) the concentrations as well. If the moles on either side of the equilibrium are unequal then the concentration must increase by unequal amounts temporarily giving proportions that are not now equal to Kc. The system then responds to RESTORE the value of Kc and in doing so moves towards the side of fewer moles.

You can demonstrate this with simple maths.

In the equation: A <==> 2C
let the [A]=a and the [C]=b

Kc = b2/a

if the pressure is then doubled (by halving the volume) then the concentration of C becomes 2b and the concentration of A becomes 2a

the ratio [products]2/[reactants] now equals 4b2/2a

which is precisely double the original ratio. The system is not at equilibrium as this ratio does not have the value of Kc and so restores the value of Kc by reducing the [products] and increasing the [reactants].

In other words the system moves towards the side of fewer moles to restore the value of Kc."

I forgot to mention that you have to take into consideration the concentration as well "K(c)".

Basically remember this,

Pressure ∝ 1/Volume
Volume ∝ 1/Concentration
 
Midnight dream

Midnight dream

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Xylferion said:
I found this explanation on another forum and it explained it very well.

"If you consider a gaseous system at equilibrium then the total number of moles is constant, the temperature is constant and so according to the gas laws if you wish to increase the pressure you MUST change the volume (decreasing it).
Concentration is given by moles/volume so you therefore change (increase) the concentrations as well. If the moles on either side of the equilibrium are unequal then the concentration must increase by unequal amounts temporarily giving proportions that are not now equal to Kc. The system then responds to RESTORE the value of Kc and in doing so moves towards the side of fewer moles.

You can demonstrate this with simple maths.

In the equation: A <==> 2C
let the [A]=a and the [C]=b

Kc = b2/a

if the pressure is then doubled (by halving the volume) then the concentration of C becomes 2b and the concentration of A becomes 2a

the ratio [products]2/[reactants] now equals 4b2/2a

which is precisely double the original ratio. The system is not at equilibrium as this ratio does not have the value of Kc and so restores the value of Kc by reducing the [products] and increasing the [reactants].

In other words the system moves towards the side of fewer moles to restore the value of Kc."

I forgot to mention that you have to take into consideration the concentration as well "K(c)".

Basically remember this,

Pressure ∝ 1/Volume
Volume ∝ 1/Concentration
Click to expand...
Thanks that helped me understand.:)
 
qwertypoiu

qwertypoiu

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devonaoki said:
Can anyone provide the reaction pathway for organic chemistry As and A2
Click to expand...
Sorry I'm not sure I understand, please make your question clear. Would you like somebody to explain all the reaction mechanisms of organic chemistry in AS and A2 syllabi?
 
qwertypoiu

qwertypoiu

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Mahnoorfatima said:
Does it make any difference if we write the structural formula of aldehyde as CH2O or as HCHO?
Click to expand...
Methanal is an aldehyde with the structural formula:
HCHO
The molecular formula may be written as:
CH2O, but this is not clear, it is always best to show organic compounds by writing structural formulas, molecular formulae may be ambiguous
 
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