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The Relationship Between Volume and Pressure (Boyle’s Law)
Concept sheet | Chemistry
Secondary
5
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Boyle’s Law is a simple gas law.
Boyle's Law
Boyle’s law describes the relationship between the pressure |(P)| and the volume |(V)| of a gas.
Consider a constant amount of gas at a given temperature. The gas occupies a certain volume and its particles exert a certain pressure due to their collisions with the walls of the container.
If the gas is compressed so that it takes up a smaller volume, the particles are more squeezed together, resulting in more collisions. The result is greater pressure on the walls of the container.
The height of the piston has an effect on the pressure exerted by the gas on the walls of the container, and its volume. Move the slider up and down to change the height of the piston.
In sum, if the number of moles |(n)| and the temperature |(T)| are constant, decreasing the volume of a gas |(V)| increases the pressure |(P)| it exerts. The other way round, when the volume increases, the pressure decreases.
Pressure is said to be inversely proportional to volume. This relationship can be expressed using the following formula.
When |T| and |n| are constant:
|P\propto\frac{1}{V}| or |PV=\text{constant}|
where
|P :| pressure often in kilopascals |(\text{kPa})|
|V :| volume often in litres |(\text{L})|
We can also compare an initial situation with a final situation in which the volume and pressure of a gas have changed. The following formula can then be used.
When |T| and |n| are constant:
|P_1V_1 = P_2V_2|
where
|P_1 :| initial pressure often in kilopascals |(\text{kPa})|
|V_1 :| initial volume often in litres |(\text{L})|
|P_2 :| final pressure often in kilopascals |(\text{kPa})|
|V_2 :| final volume often in litres |(\text{L})|
Simple gas laws apply only for ideal gases.
In other words, the values calculated using simple gas laws give us an approximation of the values that would be measured in reality. As long as the temperature is not too low and the pressure is not too high, these approximate values are very useful for predicting all kinds of situations.
At the surface of the water, a diver has a volume of |5{.}1\ \text{L}| of air in his lungs at a pressure of |101{.}3\ \text{kPa}.|
He then dives to a certain depth. Assuming that the temperature |(T)| and the amount of air |(n)| in his lungs remain the same, what would be the volume of gas in the diver's lungs?
Boyle’s Law - Example
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Exercise
Exercises coming soon.
See Also
- 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 Number of Moles (Avogadro’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)