# 1 volume of hydrogen = how many hydrogen molecules there?

• Indranil
In summary, @Indranil is on vacation for 10 days. When they return, they will need to post this question in the Homework Help forums and fill out the Template. Thanks for understanding!
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?

Indranil said:
''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?
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 said:
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

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

## 1. What is the definition of "1 volume of hydrogen"?

1 volume of hydrogen refers to the amount of hydrogen gas that occupies a volume of 22.4 liters at standard temperature and pressure (STP). This is also known as the molar volume of a gas.

## 2. How many molecules are in 1 volume of hydrogen?

There are approximately 6.02 x 10^23 molecules in 1 volume of hydrogen. This is known as Avogadro's number and is a constant value for all gases at STP.

## 3. Is 1 volume of hydrogen equal to 1 mole of hydrogen molecules?

Yes, 1 volume of hydrogen is equal to 1 mole of hydrogen molecules. This is because 1 mole of any gas contains Avogadro's number of molecules, and at STP, 1 volume of any gas occupies a volume of 22.4 liters, which is the same as 1 mole.

## 4. How does temperature and pressure affect the number of hydrogen molecules in 1 volume?

The number of hydrogen molecules in 1 volume is directly proportional to temperature and inversely proportional to pressure. This means that as temperature increases, the number of molecules also increases, but as pressure increases, the number of molecules decreases.

## 5. Can the number of molecules in 1 volume of hydrogen vary?

The number of molecules in 1 volume of hydrogen can vary depending on the conditions of temperature and pressure. However, at STP, the number of molecules is a constant value of 6.02 x 10^23, regardless of the gas being measured.

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