Gas pressure and volume
In a A reaction vessel where no reactants or products can escape or are lost to the surroundings. where the A measure of the average kinetic energy of particles in a substance. stays the same the Force exerted over an area. The greater the pressure, the greater the force exerted over the same area. of a gas increases as the The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. decreases
Remember that the A push or a pull. The unit of force is the newton (N). of the collisions do not change unless the temperature changes. If the temperature of a gas stays the same, the pressure of the gas increases as the volume of its container decreases. This is because the same number of A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. collides with the walls of the container more frequently as there is less space. However, the particles still collide with the same amount of force.
Boyle's law
The Irish scientist Robert Boyle investigated the relationship between pressure and volume in the 17th century. He trapped a bubble of air at the sealed end of a J-shaped tube using liquid mercury. He then added more mercury and observed what happened to the volume of the air bubble.
Boyle found that the higher the column of mercury in the left hand side of the tube:
- the greater the force exerted on the trapped air, the smaller the bubble became as its pressure increased
- volume is A relationship between two variables where as one variable increases, the other variable decreases, eg as the volume doubled, the pressure decreased by half. to pressure
For example, if the volume of a container is halved, the pressure is doubled. This can also be observed in a balloon of air. If the balloon is squeezed, it gets smaller.
Using Boyle's law
For a given The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of gas at a constant temperature:
pressure 脳 volume = constant
This is when:
- pressure is measured in Unit of pressure. Pascal (Pa), eg normal atmospheric pressure is 1.01x105 Pa. (Pa)
- volume is measured in metres cubed (m3)
Example
The pressure in a syringe of air is 3.00 脳 105 Pa. The volume of the gas is 5.00 脳 10-6 m3. Calculate the pressure when the volume increases to 8.00 脳 10-6 m3 at a constant temperature.
pressure 脳 volume = constant
pressure 脳 volume = 3.00 脳 105 脳 5.00 脳 10-6
= 1.50
Rearrange the equation:
\(pressure = \frac{constant}{volume}\)
\(pressure = 1.50/(8.00 \times 10^{-6})\)
\(187,500~Pa~(1.88 \times 10^5~Pa~to~3~significant~figures)\)