The Relationship Between Volume and Number of Moles (Avogadro’s Law)
Avogadro’s law is a simple gas law.
Avogadro’s Law
Avogadro’s law describes the relationship between the volume |(V)| and the quantity of gas expressed in moles |(n)|.
At constant pressure and temperature, when the quantity of gas increases, the volume it occupies increases.
Conversely, when the quantity of gas decreases, the volume decreases.
Move the slider up and down to change the number of moles in the syringe.
At constant pressure and temperature, particles maintain the same degree of agitation and the same average distance between them. Under these conditions, a larger number of particles necessarily takes up more space than a smaller number of particles.
The volume of a gas is directly proportional to its number of moles. This relationship can be expressed using the following formula.
When |P| and |T| are constant:
|V\propto n| or |\dfrac{V}{n}=\text{constante}|
where
|V :| volume often in litres |(\text{L})|
|n :| quantity of gas in moles |(\text{mol})|
We can also compare an initial situation with a final situation in which the volume and number of moles of a gas have changed by using the following formula.
When |P| and |T| are constant:
|\dfrac{V_1}{n_1} = \dfrac{V_2}{n_2}|
where
|V_1:| initial volume often in litres |(\text{L})|
|n_1:| initial quantity of gas in moles |(\text{mol})|
|V_2:| final volume often in litres |(\text{L})|
|n_2:| final quantity of gas in moles |(\text{mol})|
Find out more!
This mathematical relationship is linked to Avogadro's hypothesis, which makes it possible to determine the molar volume of a gas |(V_m),| i.e. the volume occupied by one mole of any gas under specific temperature and pressure conditions.
Be careful!
Simple gas laws only apply to ideal gases.
In other words, the values calculated using simple gas laws correspond approximately to the real values, as long as the gas temperature is not too low and its pressure not too high.
A rubber balloon with a volume of |6{.}00\ \text{L}| contains |3{.}50\ \text{mol}| of helium. The maximum volume of the balloon is |14{.}9 \ \text{L}.| How many moles of helium can be added to the balloon? Assume that the pressure and temperature remain constant.
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See Also
- The Kinetic Theory of Gases
- Simple Gas Laws
- The Relationship Between Volume and Temperature (Charles’s Law)
- The Relationship Between Pressure and Temperature (Gay-Lussac’s Law)
- The Relationship Between Volume and Pressure (Boyle’s Law)
- The Relationship Between Pressure and Number of Moles
- The General Gas Law
- The Ideal Gas Law
- The Law of Partial Pressures (Dalton’s Law)