[peterpan1372]

the initial volume was 100, it decreased by 80ml, or?

[Borek]

Answer my questions one by one.

And no, initial volume was not 100 mL.

[peterpan1372]

2moles of x reacting with 1mole of y = 2moles of z

reacting: 20ml x reacting with 10ml of y = 20ml of z, right?

Yes, that's exactly what is happening.

Now, how many mL reacted and how many mL were produced? By how many mL did the volume change? What was the initial volume? What is the final volume?

well, 20ml of x reacted, producing 20ml, too. I don't know to what you're referring to with  the rest of your questions...

[Borek]

well, 20ml of x reacted, producing 20ml, too.

No. How many mL of X reacted? How many mL of Y reacted? What was the total volume of these two reacting gases before the reaction?

(For now we are ignoring non-reacting excess of X, as it doesn't change).

[peterpan1372]

ok, hold on... we have 20ml of x reacting with 10ml of y giving 20ml of z, right?

[Borek]

ok, hold on... we have 20ml of x reacting with 10ml of y giving 20ml of z, right?

Yes. So, what was the initial volume of X and Y that reacted, and what was the final volume of produced Z? What was the volume change?

[peterpan1372]

of x we had 100, of these 20ml reacted. And 10ml of y was used up...

[Borek]

of x we had 100, of these 20ml reacted. And 10ml of y was used up...

All true so far. But I am not going to repeat other questions for the umpth time, up to you to proceed.

[peterpan1372]

my question now is: of what the volume change?? 20ml of z is the initial volume...

[Vidya]

Can someone help me out with this one?

I have 105cm^3(2*100+10)/2)

So you know that equal volume of gases have equal volume at the same temperature and pressure.
It means 2V  of X combines with 1 V of Y to give 2V of Z
One of the gases is the limiting reactant .Find out  the limiting reactant and calculate volume of Z formed from limiting reactant and volume of gas left as excess reagent.
1V of Y combines with 2V of X
so.... 10mL of Y will combine with how much volume of X?
10mL of Y will give how much volume of Z?
How much volume of X left unreacted ?

[peterpan1372]

y=limiting reactant
x-> there are 80ml left...

[Borek]

my question now is: of what the volume change?? 20ml of z is the initial volume...

Initial volume consist of 100 mL of X and 10 mL of Y. Z is not in the initial volume, as at the start of the reaction, or before reaction, it doesn't exist at all.

Final volume consists of produced Z and unreacted X that was left after the reaction went to completion.

Unreacted X doesn't change - it just sits there.

[peterpan1372]

However, this isn't still 100ml...

[Borek]

However, this isn't still 100ml...

And how am I going to guess what 100 mL you mean?

[peterpan1372]

from the solution... it says that z must be 100ml...