[Borek]

equal volumes of gases at the same temperature and pressure contain equal numbers of molecules...

And what is the relationship between moles and number molecules?

If you have identical numbers of molecules of two substances, does it mean there are identical numbers of moles?

[Borek]

we CANT know the number of moles since they are unknown...

I never asked you whether we know number of moles. I asked:

And what is the relationship between moles and number molecules?

If you have identical numbers of molecules of two substances, does it mean there are identical numbers of moles?

Your problems stem from the fact you don't know basic definitions and you don't know how to apply them. Even if we give you answers you will be still not able to solve problems, because you will not understand what you are doing. I am trying to guide through the correct line of thinking, but - sorry to say that - you are not even trying to understand questions I am asking.

[peterpan1372]

I think that I got I now!

correct me if I am wrong: since any gas has (under sam temp. and pres.) the same amount of molecules, and x and z have both 2 molecules, z must be 100, too, since x is 100 as well, or?

[Borek]

correct me if I am wrong: since any gas has (under sam temp. and pres.) the same amount of molecules

Same number of molecules in SAME volume. Please - be precise in what you write, you are leaving out details as if they were not important and in effect your statements become incorrect or ambiguous. That in turn means they need to be corrected as we have no way of knowing whether you just left them by mistake or you still have no idea what you are writing about - that's one of the reasons why we don't move forward.

and x and z have both 2 molecules, z must be 100, too, since x is 100 as well, or?

You are confusing things.

X and Z don't have "two molecules". As you said somewhere earlier, quite correctly, we don't know number of molecules of x nor z. What we do know is that:

a. one molecule of Y reacts with 2 molecules of X and produce 2 molecules of Z (that in turn means n Y molecules reacts with 2n X molecules producing 2n Z molecules)

b. per Avogadro's hypothesis under same conditions identical volumes of gas contain identical numbers of molecules.

What conclusion about volumes of reacting gases can you draw from these two facts? Can you calculate what volume of X will react with 10 mL of Y, and what volume of Z will be produced?

[peterpan1372]

yes, since 10 ml of y reacts with 100ml of 2* x, one x would equal 10 ml, too... is that right?

[peterpan1372]

but why wouldn't my initial argument be right, too?

Avogrado states:  equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

One can also say (because it is the same effect):same number of molecules, at the same temperature and pressure, have the equal number of volumes...

Since the type of gas doesnt matter => x=z

since we have also 2x and 2z, we also have the same volumes: 2x=100ml and 2z=100ml..

[Borek]

yes, since 10 ml of y reacts with 100ml of 2* x, one x would equal 10 ml, too... is that right?

10 mL of Y doesn't react with 100 mL of X, 10 mL of Y is mixed with 100 mL of X. Most of X won't react - do you understand why? There is a grain of truth in what you said about "one X". However, try to answer question I asked: what volume of X reacts and what volume of Z is produced.

One can also say (because it is the same effect):same number of molecules, at the same temperature and pressure, have the equal number of volumes...

No such thing as "equal number of volumes". I suppose you mean "same volumes".

since we have also 2x and 2z, we also have the same volumes: 2x=100ml and 2z=100ml.

If I understand correctly what you mean, you are confusing gas present with gas reacting. So no, we don't have 100 mL of X and 100 mL of Z.

Final volume is a sum of Z produced and whatever gas is left.

[peterpan1372]

ok, so we have 2 molecules of x reacting with one molecule of y,
then 20ml of x react with 10ml of y, right?

[Borek]

ok, so we have 2 molecules of x reacting with one molecule of y,
then 20ml of x react with 10ml of y, right?

Exactly.

And what volume of Z is produced?

Knowing what volume of X reacted with what volume of Y (that is: they were consumed) and what volume of Z was produced, can you calculate by how much has the volume changed?

[peterpan1372]

There are 30ml of z produced... but normally we must have 110ml of z, or?

[Borek]

There are 30ml of z produced...

No. Look at the stoichiometry, as given by the balanced reaction equation. Recheck what you read at the page I linked to earlier in the other thread (page about reading reaction equations).

but normally we must have 110ml of z, or?

No. It is not about adding volumes. You won't be able to solve the problem as long as you will not follow the stoichiometry given by the stoichiometric coefficients.

[peterpan1372]

since we have two molecules of z, we must have 60ml of z then right?

[Borek]

since we have two molecules of z, we must have 60ml of z then right?

No. Stop guessing. Where did you got 30 from? Sum of volumes of X and Y? That's not how it works, you are again and again ignoring the reaction stoichiometry.

Look at the reaction equation. Write it as "... moles of X reacting with ... mole of Y producing ... moles of Z" (fill the numbers and show them here!).

Then, knowing that ratio of volumes will be identical with the ratio of numbers of moles, write the same thing but with volumes: "... mL of X reacting with 10 mL of Y producing ... mL of Z".

[peterpan1372]

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

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

[Borek]

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?