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OCR Chemistry F322~ 4th June 2013~ AS Chemistry

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Original post by joe1545
Yea, it is just the attention to detail, i done paper today where it was 73 for an A, and in biology (also OCR) it was 65 :0


yea biology is always even lower than chemistry, because theres so many wordy answers its easy to not get the same answer as what's on the mark scheme, and I find theres quite a lot of applied/suggest questions compared to chemistry
Reply 1221
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Hello...
Original post by needtosucceed=)
if the forward reaction is exothermic, increasing the temperature shifts it to the left, in the endothermic direction
if the forward reaction is endothermic, increasing the temperate shifts it to the right, in the endothermic direction (to absorb heat and therefore decrease the temperature)
and vice versa for decreasing the temperate

increase gas moles = shifts to side with fewer moles of gas
decrease gas moles = shifts to side with more moles of gas

So in the case of the forward reaction being exothermic when increasing the temperature, what will form the most, molecules on the left hand side of the equation or molecules on the right hand side of the equation??
Original post by Jimmy20002012
Thanks soo much :biggrin: :biggrin:


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Does that make sense?
1370035727094.jpg28.5KB
Reply 1223
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wndms
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Can someone help me please?
How do you determine whether its endo or exo reaction just by looking at the chemical equation?

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Original post by wndms
Can someone help me please?
How do you determine whether its endo or exo reaction just by looking at the chemical equation?

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the enthalpy change is given next to it, and it always refers to the forward reaction. so say heres an equation
a + b = c + d deltaH = -500

the forward reaction is exothermic as its a negative enthalpy change.
Original post by Hello...
So in the case of the forward reaction being exothermic when increasing the temperature, what will form the most, molecules on the left hand side of the equation or molecules on the right hand side of the equation??


the position of equilibrium will shift to the left, in the endothermic direction, therefore more reactants and less products.
Reply 1226
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Original post by wndms
Can someone help me please?
How do you determine whether its endo or exo reaction just by looking at the chemical equation?

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If you need to know the question usually tells you, it'll be just to the right of the chemical equation usually
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Original post by needtosucceed=)
the position of equilibrium will shift to the left, in the endothermic direction, therefore more reactants and less products.

Thanks alot, that what i thought, just wanted to be sure as this is probably my worst part of the whole specification
Original post by Hello...
Thanks alot, that what i thought, just wanted to be sure as this is probably my worst part of the whole specification


thats fine :smile: I couldn't do it at all last year either. But it comes up again at a2, and now i've finally understood it lol
Original post by joe1545
Question for anyone to answer, thats prefferably not a genius although its fairly simple :wink:
In an experiment a student reacts methane (l) with HCl (l) to form Chloromethane (l) and Hydrogen Gas (g) he measures the rate of Hydrogen gas per minute... He then repeats the experiment and adds barium oxide salts (s) this time the rate of hydrogen produced in a minute increases, he observes that at the end of the reaction the barium oxide salts have sank to the bottom of the flask
Describe the affect that the barium oxide salts had on the reaction, including the type of catalyst, and how the catalyst works...

5 marks


I would probably say that The barium Oxide increases rate of reaction as you've said and that it is a heterogeneous catalyst. Basically that the catalyst is a solid and the reactants are liquids or gases. Then there are probably 3 marks for stating how a catalyst works, saying that reactants adsorb onto the surface of the catalyst, chemical reaction occurs and the products desorb from the surface.

This is probably wrong but hope it helps :smile:
Original post by wndms
Can someone help me please?
How do you determine whether its endo or exo reaction just by looking at the chemical equation?

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If energy is released e.g the temperature rises then it's exothermic, and the opposite for endothermic
Reply 1231
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Original post by needtosucceed=)
the enthalpy change is given next to it, and it always refers to the forward reaction. so say heres an equation
a + b = c + d deltaH = -500

the forward reaction is exothermic as its a negative enthalpy change.


What if it doesn't tell you? E.g. jan 2013 paper

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Reply 1232
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Original post by theo3335796
If energy is released e.g the temperature rises then it's exothermic, and the opposite for endothermic


Ohoh I get it now. Thank you.

Thanks everyone!

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Original post by wndms
What if it doesn't tell you? E.g. jan 2013 paper

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It did tell you. It said "RELEASED" - very easy to miss that word out.
Original post by wndms
What if it doesn't tell you? E.g. jan 2013 paper

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then you probably don't need to know it :smile:
Original post by Tom Winfield
I would probably say that The barium Oxide increases rate of reaction as you've said and that it is a heterogeneous catalyst. Basically that the catalyst is a solid and the reactants are liquids or gases. Then there are probably 3 marks for stating how a catalyst works, saying that reactants adsorb onto the surface of the catalyst, chemical reaction occurs and the products desorb from the surface.

This is probably wrong but hope it helps :smile:

Do you think this would get a mark: The catalyst lowers the activation energy for the reaction to proceed?
What this about heterogeneous and homogenous catalysts?

A beg somebody explain
Original post by niceguy95
What this about heterogeneous and homogenous catalysts?

A beg somebody explain


its in the textbook somewhere, under the catalyst section I think.
homogenous catalyst = reactants and catalyst are in the same state eg. yeast in the fermentation of glucose (both aqueous)
heterogeneous catalyst = reactants and catalyst are in different physical states eg. palladium/platinum catalyst in catalytic converters (reactants are gases, catalyst is a solid)

thats all you have to know.
Original post by myah_94
Do you think this would get a mark: The catalyst lowers the activation energy for the reaction to proceed?


You probably need to explain how a catalyst lowers the activation energy by adsorbing the products to its surface, weakening the bonds allowing the reaction to proceed and then desorbing the products from its surface. With a five mark question, i would want to get as much detail in to make sure i get the marks :smile:
Original post by Tom Winfield
I would probably say that The barium Oxide increases rate of reaction as you've said and that it is a heterogeneous catalyst. Basically that the catalyst is a solid and the reactants are liquids or gases. Then there are probably 3 marks for stating how a catalyst works, saying that reactants adsorb onto the surface of the catalyst, chemical reaction occurs and the products desm the surface.

This is probably wrong but hope it helps :smile:


Yea thats pretty much what i was looking for, just stating that the catalyst lowers the activation energy, and that a heterogeneous catalysis is where the catalyst is in a different phase to the reactants, ie what you said... Then the last bit is fine:smile:

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