Chemistry: Post your doubts here!

[Midnight dream]

Kc and Kp both define the rate at which a reaction proceeds, that is to assess the frequency of collisions between the reacting molecules.

When you alter the pressure of a "gas", the equilibrium " position " shifts to the side with a higher/lower amount of moles. With that in mind, the equilibrium position is devoting itself to counteract the change, everything is attempting to balance out.

To match the increase/decrease, the position of equilibrium has to adjust in order decrease/increase the change accordingly. So all that the change in pressure is doing, is telling the Position of equilibrium to shift back to cancel out this change, it is not increasing the rate of the reaction.

On the other hand, temperature affects the rate at which the reaction proceeds. Since molecules with more energy, will raise the frequency of collisions.

For a change in pressure, it's not trying to get the reaction to move faster, it's like a jug of water, when you fill it past its capacity, the rest will spill. What that simply means is, to deal with all this compressed high pressure gas, it attempts to spread the gas molecules out evenly so as to achieve a pressure that's suitable to both sides. It is not making molecules collide more.

Hope that explains it.

It was a very good explanation.

But i have a query.Since pressure is increased, It means that the volume has decreased. Now the particles will be closer together and the chances of collision has increased.Won't it make the molecules collide more?
And also, Doesn't a change in pressure causes the reaction to go faster?

 

[Mahnoorfatima]

Hydrolysis using an alkaline catalyst. The catalyst being KOH in this reaction. The ester splits up into [CH3CO2] belonging to the carboxylic acid, and [CH(CH3)CH3] belonging to the alcohol.

First step,

CH3CO2CH(CH3)CH3 reacts with the OH- ion to form a carboxylate ion and an alcohol.

The carboxylate ion, which is negative, bonds with K.

CH3CO2K + HOCH(CH3)CH3

Second step,

Have CH3CO2K react with a hydrogen halide, like HCl.

CH3CO2K + HCl ------> CH3COOH + KCl

The products can be either CH3COOH and HOCH(CH3)CH3, OR CH3CO2K and HOCH(CH3)CH3.Hope this helped though..

Do you have a source for this question?



this is ON 12 P23 Qs 4. Could you please solve the other questions that I actually had to ask instead of what I posted before?

 

[Mahnoorfatima]

Can someone please post ER's of chemisry? I can't find them anywhere and papers are not opening over here!

 

[Xylferion]

It was a very good explanation.

But i have a query.Since pressure is increased, It means that the volume has decreased. Now the particles will be closer together and the chances of collision has increased.Won't it make the molecules collide more?
And also, Doesn't a change in pressure causes the reaction to go faster?

It's because of the fact that the volume is low and the gas is under high pressure, that it wants to expand and move to the side with the fewer moles. Equilibrium will counteract whatever change pressure makes. This would not be the case if you were considering a non-equilibria based question.

 

[Xylferion]

Can someone please post ER's of chemisry? I can't find them anywhere and papers are not opening over here!

http://www.examtestprep.com/

 

[Midnight dream]

It's because of the fact that the volume is low and the gas is under high pressure, that it wants to expand and move to the side with the fewer moles. Equilibrium will counteract whatever change pressure makes. This would not be the case if you were considering a non-equilibria based question.

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?

 

[Xylferion]

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?

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]

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

Thanks that helped me understand.

 

[devonaoki]

Can anyone provide the reaction pathway for organic chemistry As and A2

 

[qwertypoiu]

Thanks that helped me understand.

Here's another link which might help you:
http://www.chemguide.co.uk/physical/equilibria/change.html
The website itself has nice content.

 

[qwertypoiu]

Can anyone provide the reaction pathway for organic chemistry As and A2

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?

 

[Mahnoorfatima]

https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9701_s12_qp_23.pdf
Question 5 part d? How are we supposed to know the compound. I get the next k2cr2o7 but I don't get what compounds isomers do I draw!?

 

[Mahnoorfatima]

http://www.examtestprep.com/

Sorry for bothering you time and again but I can't find Examiner reports. :/

 

[Mahnoorfatima]

Does it make any difference if we write the structural formula of aldehyde as CH2O or as HCHO?

 

[qwertypoiu]

Sorry for bothering you time and again but I can't find Examiner reports. :/

http://onlineexamhelp.com/wp-content/uploads/2013/10/9701_s13_er.pdf
Manipulate letters and numbers

 

[qwertypoiu]

Does it make any difference if we write the structural formula of aldehyde as CH2O or as HCHO?

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

 

[Midnight dream]

Here's another link which might help you:
http://www.chemguide.co.uk/physical/equilibria/change.html
The website itself has nice content.

you are a life saver.Thanks.

 

[qwertypoiu]

you are a life saver.Thanks.

Np buddy glad it helped you

 

[Lola_sweet]

What is a binary compound?

 

[qwertypoiu]

What is a binary compound?

A binary compound is a chemical compoundthat contains exactly two differentelements.[1][2] Examples of binary ionic compounds include calcium chloride (CaCl2),sodium fluoride (NaF), and magnesium oxide(MgO), whilst examples of a binary covalent compounds include water (H2O), and sulfur hexafluoride (SF6).