1 volume of hydrogen = how many hydrogen molecules there?

[Indranil]

''1 volume of hydrogen + 1 volume of hydrogen + 1 volume of oxygen = 2 volumes of water vapor''
Now my questions are as follows:
1. How many hydrogen molecules in 1 volume of hydrogen?
2. How many oxygen molecules in 1 volume of oxygen?
3. how many water vapor molecules in 2 volumes of water vapor?
How to calculate? please explain.

 

[tnich]

''1 volume of hydrogen + 1 volume of hydrogen + 1 volume of oxygen = 2 volumes of water vapor''
Now my questions are as follows:
1. How many hydrogen molecules in 1 volume of hydrogen?
2. How many oxygen molecules in 1 volume of oxygen?
3. how many water vapor molecules in 2 volumes of water vapor?
How to calculate? please explain.

I think what you are looking for is the ideal gas law, which would allow you to calculate the number of molecules of gas in a given volume if you know the temperature and pressure. This is expressed as
$$PV=nRT$$
where
P is pressure
V is volume
n is the number of moles of gas
R is the universal gas constant
T is the absolute temperature
All of these variables should be expressed in SI units.
The number of molecules in a mole is Avogadro's number. You can do a search on the ideal gas law for more details.
The statement of your problem implicitly assumes that the temperature and pressure are the same before and after the chemical reaction. This is not true in general.

 

[tnich]

I think what you are looking for is the ideal gas law, which would allow you to calculate the number of molecules of gas in a given volume if you know the temperature and pressure. This is expressed as
$$PV=nRT$$
where
P is pressure
V is volume
n is the number of moles of gas
R is the universal gas constant
T is the absolute temperature
All of these variables should be expressed in SI units.
The number of molecules in a mole is Avogadro's number. You can do a search on the ideal gas law for more details.
The statement of your problem implicitly assumes that the temperature and pressure are the same before and after the chemical reaction. This is not true in general.

A more precise way to state the chemical equation for combining hydrogen with oxygen would be:

2 moles of hydrogen molecules + 1 mole of oxygen molecules results in 2 moles of water vapor

or equivalently

2 H₂ + 1 O₂ → 2 H₂O

 

[berkeman]

Looks like @Indranil has started a 10-day vacation from the PF. When s/he returns, they need to post this question in the Homework Help forums, and fill out the Template. This thread will stay closed but visible to help with great hints from @tnich