OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012

Original post by volvicstar

yes how did you get there?

1) Write out the equation: N2+ 3H2 -> 2NH3
2) Write Kc expression: [NH3]2/[N2]

3

then sub in the values you know e.g. kc and concentration of N2 and H2, then rearrange to give sqroot(8.00X10^-2X9.6) = 0.8763...
therefore 0.88 moldm3

Hope that helps.

Reply 1783

Original post by Bright

1) Write out the equation: N2+ 3H2 -> 2NH3
2) Write Kc expression: [NH3]2/[N2]

3

then sub in the values you know e.g. kc and concentration of N2 and H2, then rearrange to give sqroot(8.00X10^-2X9.6) = 0.8763...
therefore 0.88 moldm3

Hope that helps.

salam khobi bright chi khabar? you know the specimen paper why is c2h4 1st order should be 2nd order cause the rate doubles/

Reply 1784

heythereimannie

Original post by pete clark

No, you need to compare the experiments, AND the rate of reaction.. So experiment 1+2, the concentration of Ozone goes up by 4.. and so does the rate of reaction.. So you know the Ozone is directly proportional to the rate of reaction. Then compare experiment 2+3, the conc of Ozone doubles, however the rate goes up by 4, too. So that shows you that Ethene is first order as well..

So the rate equation is..
rate=k[O3][C2H4]

help? :smile:

Ohhhh right, I can't believe I didn't get it, that makes so much sense!

Thank you :smile:

Reply 1785

pete clark

Original post by heythereimannie

Ohhhh right, I can't believe I didn't get it, that makes so much sense!

Thank you :smile:

No problem, good luck for Wednesday. :smile:

Reply 1786

Original post by pete clark

No problem, good luck for Wednesday. :smile:

hi pete clark how are u :wink:

why was is it 1st order not second not getting it cause usally you need to have the concentrations the same to be able to compare the experiment?

Reply 1787

ChrisJ

Original post by Killjoy-

Thank you.
Our teacher gave us a mix of questions so I didn't know where they came from.

Do you think I should just do unifying concepts or should I look at these as well?
How far, how fast?
Trends and patterns
Transition elements

I haven't looked at any of those other ones, but from a quick look at some of the papers I would say unifying concepts looks more relevant to our spec.

Reply 1788

pete clark

Original post by otrivine

hi pete clark how are u :wink:

why was is it 1st order not second not getting it cause usally you need to have the concentrations the same to be able to compare the experiment?

Compare Exp 1+2, Conc of ethene stays the same. Conc of Ozone increases by a factor of 4, as does the rate of reaction.. so you know Ozone is first order..

Then compare exp 2+3. Ozone concentration doubles in exp 3 compared to exp 2, and if the conc of ethene was the same in both experiment, the rate would also double, however the concentration of Ethene doubles as well. so the rate increases by 4. :smile:

Reply 1789

Original post by pete clark

Compare Exp 1+2, Conc of ethene stays the same. Conc of Ozone increases by a factor of 4, as does the rate of reaction.. so you know Ozone is first order..

Then compare exp 2+3. Ozone concentration doubles in exp 3 compared to exp 2, and if the conc of ethene was the same in both experiment, the rate would also double, however the concentration of Ethene doubles as well. so the rate increases by 4. :smile:

ok right so when we have two same like 1 and 1 we compare experiments 1 and 2 if the concentration of o3 is not the same in any experiments correct?

Reply 1790

Dollyandra

8

Hey guys does anyone know of any websites for ionic equations right from the ground up? I just can't get my head around them! I seem to have developed a mental block...I can do cells and redox equations, but every now and again I get really caught out because I don't fully understand the principle behind it :frown:

Reply 1791

Killjoy-

8

Original post by Dollyandra

Hey guys does anyone know of any websites for ionic equations right from the ground up? I just can't get my head around them! I seem to have developed a mental block...I can do cells and redox equations, but every now and again I get really caught out because I don't fully understand the principle behind it :frown:

Google knockhardy or chemguide.
(Chemguide will probably be better for this topic.)

Reply 1792

Original post by otrivine

salam khobi bright chi khabar? you know the specimen paper why is c2h4 1st order should be 2nd order cause the rate doubles/

Salam I'm good shoma?

Did you understand why or do you want me to explain?

Reply 1793

Original post by Bright

Salam I'm good shoma?

Did you understand why or do you want me to explain?

merci

na i did not get it is it because if the concentration of o3 has no same conc but for o3 if 1.0 and 1.0 is same we use experiments 1 and 2?

Reply 1794

Issy123

can someone ask a few chemistry questions please :colondollar:

Reply 1795

niaghez

Original post by Bright

1) Write out the equation: N2+ 3H2 -> 2NH3
2) Write Kc expression: [NH3]2/[N2]

3

then sub in the values you know e.g. kc and concentration of N2 and H2, then rearrange to give sqroot(8.00X10^-2X9.6) = 0.8763...
therefore 0.88 moldm3

Hope that helps.

what! are you iranian too??

Reply 1796

lukas1051

18

How does a fuel cell produce a current? I still don't understand...

Reply 1797

Original post by otrivine

merci

na i did not get it is it because if the concentration of o3 has no same conc but for o3 if 1.0 and 1.0 is same we use experiments 1 and 2?

For O3 use exp 1 and 2
[O3] X4
Rate X4
->first order

For C2H4 use exp 2 and 3
[C2H4]X2
Rate, we know that O2 is 1st order, conc has increased by X2, so multiply rate as well by 2 giving you 8, then see the connection between the new rate (8) and given rate (16) which is X2.

So that shows C2H4 is also first order.

Dorost shod?

Reply 1798

username510760

1

Does anyone have the January 12 past paper for this exam?
I did have a page bookmared with it on but the thread seems to have disappeared.

Reply 1799