Particle model and pressure
Particle motion in gases
The molecules of a gas are in a constant random motion.
When the molecules collide with the wall of their container, they exert a force on the wall.
The total force exerted by all of the molecules inside the container on a unit area of the walls is the gas pressure.
2 factors affecting gas pressure:
Temperature-If the temperature is increased, particles have higher kinetic energy. This means there are more collisions per second.
Volume-Reducing the space particles have to move in increases the number of collisions and therefore the gas pressure.
Pressure=force/area
Force=Newtons
Area-Metres
Pressure in gases
The pressure of a gas is due to the particles colliding with the walls of the container that the gas is held in.
The particle collisions cause a force which acts at right angles to the walls of the gas container.
The force, acting over the area of the container, causes the gas pressure.
The pressure of a gas is inversely proportional to the volume. If the volume increases, then the pressure decreases.
pV=constant
Increasing the pressure of gas
Work is the transfer of energy by a force. When you compress a gas the internal energy increases which leads to the increase of temperature of the gas(kinetic energy is increased).
Adding more particles to a fixed volume
o Doing work on a gas means compressing or expanding the gas, so changing the volume
o Pumping more gas into the same volume means more particles are present, so more collisions occur per unit time with the walls, so pressure increases.
o Energy is transferred to the particles when more gas is added into the fixed volume, so this heats the gas
- A fixed number of particles for a smaller volume
o The particles collide with the wall which is moving inward
o So the particles gain momentum, as the rebound velocity is greater than the approaching velocity
o So as the particle has a greater velocity, the pressure increases as the particles collide with the walls more frequently (time between collisions decreases)
oAnd the temperature also increases, as the kinetic energy of each particle increases.
Bicycle pumps tend to get warm when we use them to inflate a tyre. That is because we are doing work on the gas, increasing its internal energy.