Question

This is a multiple choice question but i don't want a direct answer :) I just need an explanation on how to interpret the graph because i've never come across a question like this :) please help!
http://prntscr.com/5zcwvc

Answer 1

I'm thinking that it's C ?

Answer 2

whats your reasoning?

Answer 3

Well both lines level out and remain constant after 2 hours... and i'm guessing that when they've established equilibrium ?

Answer 4

yep thats how i see it too

Answer 5

B and D are nonsense
A and C left

Answer 6

C does seem to be right to me as after from 0 to 2 the reactant was just changing to product but at 2 they crossed which means rate at which reactant was converted to product is same as rate at which product was converted to reactant = equilibrium point

Answer 7

what do you think about A?

Answer 8

Originally i was deciphering between A and C. I still think it's C though...?
I'm not too sure about A but i don't think that their equilibrium concentrations were 0.2 mol L^-1 because the curve were still increasing / decreasing at that point? So it couldn't be an equilibrium point.

Answer 9

equilibrium concentration is the concentration of product or reactant at which equilibrium is reached
isnt it?

Answer 10

hmmmmm its kind of confusing but now i think its A because at 2mole L we see equilibrium but when its less or more than that - there is no equilibrium
so equilibrium is reached at 2nd hour but it does not continue

Answer 11

while option C says that equilibrium is reached AFTER 2 hours - so we'd expect the rest of the graph to show equilibrium after 2nd hour
while the graph shows at exactly 2nd hour when concentration is 2moleL

Answer 12

@aaronq @Kainui can you check if i am understanding right? or wrong?

Answer 13

we'll cross check with the other guys just in case to makes sure we are getting whats going one
okay? :)

Answer 14

xD okay! :)
I'm kinda confused between A and C now xD

Answer 15

Wait the way I was looking at it was that almost everything was right except A, I just woke up so I could probably use a slap if I'm wrong, so I'll say it anyways in case I'm right.

See, it isn't until around 4 hours that the system reaches equilibrium. The reaction hasn't stabilized until then, so it seems fair to say that C reached equilibrium after 2 hours but it would have been better if the question said they reached equilibrium by 4 hours I guess.

The reaction started out with .4M of reactants and 0M of products right? So if we follow the lines we see that the .4M of starting material went down to .1M of material but never fully went away. I might be off on my terminology on what it means for a reaction to go to completion means, but since there is still .1M left of starting material it seems like the reaction didn't go to completion. So D is also correct. Unless of course "going to completion" means "reaching equilibrium".

B seems right but I'm not sure what they mean exactly. In a sense the forward reaction did stop after 4 hours so it seems right, but since this is chemistry, this isn't a static stop of reactions. This is dynamic equilibrium, so that means after 4 hours the rate of the reaction in the forward direction matches exactly that of the reaction rate in the opposite direction. So it's kind up to interpretation, I feel like in some sense I'm either over analyzing it or this is the concept of dynamic equilibrium they're trying to trick you on.

A is completely wrong, it is at .2M concentration when they both are of equal concentrations but that's it since shortly after that the concentrations change, definitely not an equilibrium.

I hope that helps!

Answer 16

@Kainui thaaaaaaaaaanks! i was pretty sure i was wrong lol

Answer 17

lol oh well, there's too much in chemistry honestly

Answer 18

@Kainui yep & you do know i hate/dont get equilibrium lol

Answer 19

If I ever have a girl, I'm going to name her first and middle names Kate Ronstant

Answer 20

oh dear xD I just woke up and read your explanation @Kainui . Can i just say... i am more confused than ever before hahaha xD I think.. i'll just stick with C or something..
This is way too confusing for a multiple choice question to be honest LOL

Answer 21

@eric_d

Answer 22

i would argue that the right answer is actually D, since A is clearly not correct, B is nonsense, and as @kainui has already mentioned, C is out

Answer 23

the phrase "going to completion" usually means that 100% of the reactants form products, with no reactants left over, and so there is no "reverse" reaction for equilibrium taking place

Answer 24

oohhhhhhhh. That kinda makes more sense! So D it is.
Thanks for your all the help and contribution @Somy , @Kainui and @JFraser !! :)

Answer 25

no problem tho i made you more confused & was wrong T_T sowwyy :)

Answer 26

hahaha it's okay! :)

Answer 27

I agree with D