Concentration and equilibrium graph HSC question (1 Viewer)

[BlueGas]

I need help with this question, I know the answer for the marking guidelines but I want to know why/how this answer was chosen.

 

[rand_althor]

As CH3OH is a product, its initial concentration would be zero as the reactants haven't reacted to form it yet. This means the bottom dashed line represents CH3OH. Over time as the CH3OH is being made, the middle dashed line decreases so that it has a value half that of the solid line. This indicates that the middle dashed line is the H2, as in the reaction it has a molar ratio of 2:1 with CO. So that leaves the solid line at the top to be CO. From this, you can see that at T1 H2 is added, and at T2 CH3OH is removed. So the answer is A.

 

[BlueGas]

As CH3OH is a product, its initial concentration would be zero as the reactants haven't reacted to form it yet. This means the bottom dashed line represents CH3OH. Over time as the CH3OH is being made, the middle dashed line decreases so that it has a value half that of the solid line. This indicates that the middle dashed line is the H2, as in the reaction it has a molar ratio of 2:1 with CO. So that leaves the solid line at the top to be CO. From this, you can see that at T1 H2 is added, and at T2 CH3OH is removed. So the answer is A.

Oh okay, I understand that CH3OH's initial concentration is 0, but the H2 and CO part confuses me, is there a simpler way to know which curve is for which?

 

[rand_althor]

Oh okay, I understand that CH3OH's initial concentration is 0, but the H2 and CO part confuses me, is there a simpler way to know which curve is for which?

From the reaction, you can see that CO and H2 react in a 1:2 ratio. This means that for every 1 mole of CO, 2 moles of H2 is required to produce CH3OH. This also means that their molar concentrations are also in the ratio 1:2. Let's number the y-axis from 0M to 10M, with increments every 1M. Both CO and H2 start at an initial concentration of 10M. At time T1, the solid line has dropped to 7M, and the middle dashed line has dropped to 4M. The middle dashed line has dropped double the amount that the solid line has, i.e. the substance being represented by the middle dashed line has been used up twice as much as the substance being represented by the solid line. Since we know that CO and H2 react in a 1:2 ratio, this means that the solid line represents CO and the middle dashed line represents H2.

 

[Librah]

Oh okay, I understand that CH3OH's initial concentration is 0, but the H2 and CO part confuses me, is there a simpler way to know which curve is for which?

It doesn't get simpler than that.

 

[BlueGas]

I think I kind of get it now...