HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[HeroicPandas]

re: HSC Chemistry Marathon Archive

External things that can impact the shape of the graphs and it all depends on the states of reactant and products and whether there is an enthalpy change. Changes include:

-addition or removal of reactants and products (hence changing their concentration), an addition causes a sharp increase, removal causes a sharp decrease. If adding or removing solids or liquids, equilibrium is not affected as these have a constant concentration

- increase or decrease in pressure (or volume of system), increasing pressure (or decreasing vol.) will cause a sharp increase in both reactants and products, vice versa for decreasing in pressure

-increase or decrease in temperature (depending if reaction is exothermic/endothermic and if none, then temperature has no effect), changing temperature has no immediate effect on the system, but it causes the system to adjust to minimise the change (Le Chatelier's Principle), hence causing a smooth decrease/increase

Furthermore, after a change has occured, the system will shift to oppose the change, attempting to minimise the disturbance (Le Chatelier's Principle), and hence the curve will smooth out AFTER conc/pressure/temp has been altered


right or wrong? lol

 

[Sy123]

re: HSC Chemistry Marathon Archive

External things that can impact the shape of the graphs and it all depends on the states of reactant and products and whether there is an enthalpy change. Changes include:

-addition or removal of reactants and products (hence changing their concentration), an addition causes a sharp increase, removal causes a sharp decrease. If adding or removing solids or liquids, equilibrium is not affected as these have a constant concentration

- increase or decrease in pressure (or volume of system), increasing pressure (or decreasing vol.) will cause a sharp increase in both reactants and products, vice versa for decreasing in pressure

-increase or decrease in temperature (depending if reaction is exothermic/endothermic and if none, then temperature has no effect), changing temperature has no immediate effect on the system, but it causes the system to adjust to minimise the change (Le Chatelier's Principle), hence causing a smooth decrease/increase

Furthermore, after a change has occured, the system will shift to oppose the change, attempting to minimise the disturbance (Le Chatelier's Principle), and hence the curve will smooth out AFTER conc/pressure/temp has been altered


right or wrong? lol

I think that's right, but what about liquids, why don't they affect the system when you draw some out?

I'd like a second opinion on this though

 

[Menomaths]

re: HSC Chemistry Marathon Archive

I think that's right, but what about liquids, why don't they affect the system when you draw some out?

I'd like a second opinion on this though

Pretty sure addition/removal of a solution affects equilibrium, it's only solids that don't.

I'd like a third opinion on this though.

 

[bedpotato]

re: HSC Chemistry Marathon Archive

Pretty sure addition/removal of a solution affects equilibrium, it's only solids that don't.

I'd like a third opinion on this though.

99% sure they do. It's only pressure and volume that are affected by only gases, right?

I'd like a fourth opinion on this though.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

99% sure they do. It's only pressure and volume that are affected by only gases, right?

I'd like a fourth opinion on this though.

Yeah, that's correct.
(sorry for breaking chain)

 

[bangladesh]

re: HSC Chemistry Marathon Archive

Yeah, that's correct.
(sorry for breaking chain)

damn it. Why'd you have to break the chain. I'm devo now.

 

[superSAIyan2]

re: HSC Chemistry Marathon Archive

Pretty sure addition/removal of a solution affects equilibrium, it's only solids that don't.

I'd like a third opinion on this though.

A solution is not the same as a liquid.
I think Heroic is right. Liquids have a constant concentration and will not affect equilibrium. Only the addition/removal of gases and aqueous solutions do have an effect.

Edit: for industrial students, remember when you calculate K you only factor in gases and aqueous solns

 

[Menomaths]

re: HSC Chemistry Marathon Archive

A solution is not the same as a liquid.
I think Heroic is right. Liquids have a constant concentration and will not affect equilibrium. Only the addition/removal of gases and aqueous solutions do have an effect.

Oh right different things my bad.
Note to self: Never challenge Heroic again

 

[Sy123]

re: HSC Chemistry Marathon Archive

A solution is not the same as a liquid.
I think Heroic is right. Liquids have a constant concentration and will not affect equilibrium. Only the addition/removal of gases and aqueous solutions do have an effect.

Edit: for industrial students, remember when you calculate K you only factor in gases and aqueous solns

Ahhh yess my bad

 

[bedpotato]

re: HSC Chemistry Marathon Archive

A solution is not the same as a liquid.
I think Heroic is right. Liquids have a constant concentration and will not affect equilibrium. Only the addition/removal of gases and aqueous solutions do have an effect.

Edit: for industrial students, remember when you calculate K you only factor in gases and aqueous solns

Hmm, okay.

CO2 + H2O <---> H2CO3
So, adding water won't affect the equilibtrium?

 

[someth1ng]

I gave him 1 mark because he didn't answer the question. It's not unusual.

You can lose 6 marks from a 7 marker if you don't include at least 2 correct equations if it says to include "equations".

so no, 1/5 is not harsh at all. In my opinion, I feel that it's hardly deserving of even that.

 

[superSAIyan2]

re: HSC Chemistry Marathon Archive

Lol now im confused about the whole liquids thing. In esterification the textbook says that a sulfuric acid catalyst is used to remove water from the system to shift the equilibrium to favour ester yield. But liquids aren't supposed to affect equilibrium position.

Does this mean water is a gas? or is it because removing water will increase the concentration of the alkanoic acid (which is an aqueous solution) and this will shift the equilibrium to favour the ester yield?

 

[bedpotato]

re: HSC Chemistry Marathon Archive

Lol now im confused about the whole liquids thing. In esterification the textbook says that a sulfuric acid catalyst is used to remove water from the system to shift the equilibrium to favour ester yield. But liquids aren't supposed to affect equilibrium position.

Does this mean water is a gas? or is it because removing water will increase the concentration of the alkanoic acid (which is an aqueous solution) and this will shift the equilibrium to favour the ester yield?

If so, can't this be applied to other liquids as well?

 

[Menomaths]

re: HSC Chemistry Marathon Archive

chm so cnfsing

y u do dis chm ;(

 

[superSAIyan2]

re: HSC Chemistry Marathon Archive

If so, can't this be applied to other liquids as well?

Dont think so. Aqueous solutions are dissolved in water. So maybe water is a special case.

 

[bangladesh]

re: HSC Chemistry Marathon Archive

LOL. I don't do industrial so I'm not confused at all hehe.
As for the CO2 + H2O <---> H2CO3
Adding water shifts the equilibrium to the right as far as I know.

 

[superSAIyan2]

re: HSC Chemistry Marathon Archive

maybe water is the only liquid that can affect an equilibrium, even though it has a constant concentration. I think that the proper explanation is that adding water will decrease the concetration of H2CO3 which causes the equilibrium to shift right

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Looking back, it's dodgy to say that water affects equilibrium in this case because it's separated into a different phase - the ester isn't soluble in water and vice versa. But yes, H2SO4 is hydrophilic and will help pull water out of the ester.

However, water can affect equilibrium - liquid only don't affect equilibrium when them main equilibrium is established in a gas phase (Haber process). If the NH3 condensed out of the reaction vessel, it wouldn't affect equilibrium. In fact, only solids don't affect equilibrium.

Using NaCl and CH3COOH as examples:

NaCl_(s)⇌Na⁺_(aq)+Cl^-_(aq)
In a saturated solution, there is equilibrium between aqueous sodium chloride and solid sodium chloride. Adding more solid sodium chloride will not affect equilibrium.

CH3COOH+H2O⇌H3O⁺+CH3COO^-
Add more water and you shift equilibrium to the right.

Clearly, liquids CAN affect equilibrium, so can gases.

In general, it just depends on where the equilibrium is established - if the equilibrium is established in the gas phase, liquids and solids won't affect it. If the equilibrium is established in the liquid phase, gases and solids won't affect it.

Clear?

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Looking back, it's dodgy to say that water affects equilibrium in this case because it's separated into a different phase - the ester isn't soluble in water and vice versa. But yes, H2SO4 is hydrophilic and will help pull water out of the ester.

However, water can affect equilibrium - liquid only don't affect equilibrium when them main equilibrium is established in a gas phase (Haber process). If the NH3 condensed out of the reaction vessel, it wouldn't affect equilibrium. In fact, only solids don't affect equilibrium.

Using NaCl and CH3COOH as examples:

NaCl_(s)⇌Na⁺_(aq)+Cl^-_(aq)
In a saturated solution, there is equilibrium between aqueous sodium chloride and solid sodium chloride. Adding more solid sodium chloride will not affect equilibrium.

CH3COOH+H2O⇌H3O⁺+CH3COO^-
Add more water and you shift equilibrium to the right.

Soooo liquids don't affect equilibrium?

edit:nvm just saw your edit

 

[bangladesh]

re: HSC Chemistry Marathon Archive

Looking back, it's dodgy to say that water affects equilibrium in this case because it's separated into a different phase - the ester isn't soluble in water and vice versa. But yes, H2SO4 is hydrophilic and will help pull water out of the ester.

However, water can affect equilibrium - liquid only don't affect equilibrium when them main equilibrium is established in a gas phase (Haber process). If the NH3 condensed out of the reaction vessel, it wouldn't affect equilibrium. In fact, only solids don't affect equilibrium.

Using NaCl and CH3COOH as examples:

NaCl_(s)⇌Na⁺_(aq)+Cl^-_(aq)
In a saturated solution, there is equilibrium between aqueous sodium chloride and solid sodium chloride. Adding more solid sodium chloride will not affect equilibrium.

CH3COOH+H2O⇌H3O⁺+CH3COO^-
Add more water and you shift equilibrium to the right.

Clearly, liquids CAN affect equilibrium, so can gases.

In general, it just depends on where the equilibrium is established - if the equilibrium is established in the gas phase, liquids and solids won't affect it. If the equilibrium is established in the liquid phase, gases and solids won't affect it.

+1