Edexcel IGCSE Chemistry 18th May/June 2017 Thread

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Reply 80

gpit6903

Original post by archibald300

Yh I swear that's how you're supposed to work it out right?

Yeah think so it was the only way I could work its empircal formula out, man im so tired.....

Reply 81

Darwinion

I'm not great on reversible reactions. One question was about a change in pressure and the effect on the rate... I think. And one was an increase in temp and the effect on yield?

It was slightly exothermic... wasn't the enthalpy change -9 kJ?

A pressure difference would alter the rate of reaction.... but not affect any yield if 2 moles were produced either way. But I cannnot remember what way round the questions were. :tongue:

(edited 6 years ago)

Reply 82

not_XIX_forever

Don't worry - a lot of my friends got the same too :smile:

Me too! I have officially completed 6 out of 28 exams!
Just take a short break, then get back to revising otherwise you feel really guilty for not doing stuff which is the worst. :smile:

Have you got an exam tmoz?

Original post by gpit6903

Yeah think so it was the only way I could work its empircal formula out, man im so tired.....

Reply 83

gpit6903

Original post by Darwinion

I'm not great on reversible reactions. One question was about a change in pressure and the effect on the rate... I think. And one was an increase in temp and the effect on yield?

Is anyone going to upload a unofficial marking scheme,

we need to try and remember the questions....

Increase in temp and pressure = increase in rate of reaction

increase in pressure = no change in yield

increase in temp = less yield (i think it asked that or equivalent other way round)

Reply 84

not_XIX_forever

For both the rate decreased
For the temp one the yield increased ( i think - forward react was exo?)
For pressure i put no change because 2 moles either side

Original post by Emm22

What answers did you guys get for the equilibrium questions?

Reply 85

Emm22

Original post by gpit6903

The question was for equilibrium:
Originally at 500 degrees then they asked how a lower temp of 400 would effect rate and yield

Lowered pressure from 4atm to 2atm and asked in effect on the rate and yield

Reply 86

Queenie123

i thought pressure didn't have an effect on rate of reaction??

Reply 87

gpit6903

Original post by Emm22

Either way I think i got it the right way round, or answered the question completely wrong.... oh well

I hate forgetting the questions after

Reply 88

Emm22

Original post by Queenie123

i thought pressure didn't have an effect on rate of reaction??

I don't know, does a lower pressure affect the rate of reaction

Reply 89

JMR2021_

Debate & Current Affairs Helper

For the one where you had to find the x of h2o, I did not really understand it and I wrote 8 as an answer.
Next to the equation I wrote the mass, molar mass and moles for each, but do you think I would get any marks for this?

Reply 90

gpit6903

Original post by Emm22

I don't know, does a lower pressure affect the rate of reaction

increasing the pressure on a reaction involving reacting gases increases the rate of reaction...

(
http://www.chemguide.co.uk/physical/basicrates/pressure.html)

so i guess a lower pressure equals a lower rate of reaction

(edited 6 years ago)

Reply 91

ITSJDOG

How did you guys find the paper in general? Because I'm having bad feeling about how I've done in mine!😬

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Reply 92

georgetbarber

How did people include all those symbols for the galvanisation one?

Reply 93

sportygal517

Original post by Queenie123

i thought pressure didn't have an effect on rate of reaction??

No it does, pressure and temperature have an effect on the yield, its the catalyst that doesn't have any effect on the yield

Reply 94

Darwinion

Ahhh yes! The temperature in the question was lowered to 400 not raised. So the forward yield increased as the reaction was exothermic. The equilibrium moves in the direction to counteract any change.

Increase in pressure always increases rate as there is less space for the particles to move around in so they collide more frequently. But it won't increase yield if the same number of moles are produced both ways (as was the case in our question).

(edited 6 years ago)

Reply 95

Revision1011

I found it okish although I messed up the % of oxygen question. You'll be fine don't worry 😊

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Reply 96

Glazmann

Original post by ITSJDOG

How did you guys find the paper in general? Because I'm having bad feeling about how I've done in mine!😬

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same- I was completely not confident in my answers, unlike biology. My friend said she found the chemistry easier than the biology, but for me, it was the other way around!