what do the random collisions of gas particles in a container add up to produce
- a net force
- at right angles to the wall of the container
what rule always applies unless a gas container is in a vacuum
- the gas container will be under pressure from whatever is around it
- such as atmospheric pressure from the air
why can containers without a fixed volume such as balloons remain a constant volume
- because the pressure of the gas pushing outwards from inside the balloon
- is equal to the pressure of the air pushing inwards
how can you change the volume of a gas in a container that doesnt have a fixed volume
- by changing the internal (outward)
- or external (inward) pressure on the container
what does the heating or cooling of a balloon with gas in it simply do
changes the pressure of gas inside a container
what happens to the gas particles in a balloon as it gets heated
- they gain more kinetic energy and move around quicker
- which increases the pressure of the gas inside the balloon
why does heating a balloon cause it to expand
- the increase in kinetic energy results in the increase in pressure on the balloon
- this means that the outward pressure of the gas inside the balloon is larger than the inward pressure outside it
- this causes the balloon, and so the volume of gas, to expand until the pressure is equal once more
what happens when you cool a balloon
- the gas particles lose their kinetic energy
- so the outward pressure in the balloon is smaller than the inward pressure from the surroundings pushing into the balloon
- so the gas inside the balloon, and therefore the balloon itself, is compressed
what are the two examples of ways the external pressure on a gas can change
- pushing hard on the plunger of an air-tight gas syringe
- or investigating the relationships between atmospheric pressure and altitude
what is the effect of pushing hard on the plunger of an air-tight gas syringe
- it increases the inward pressure of the gas
- so that it is larger than the outward pressure
- this causes the gas inside the syringe to be compressed
what is the relationship between atmospheric pressure and altitude
- atmospheric pressure decreases as altitude increases
- so as the container of gas rises
- the inward pressure decreases
- this causes the gas to expand as the altitude increases
what does doing work on a gas do
increase its internal energy which increases its temperature
what are two examples of the ways that you can do work on gas
- mechanically, such as using a bike pump
- or by heating the gas
why is work done when someone uses a bike or gas pump
- the gas exerts pressure of the plunger of the pump
- so it therefore exerts a force on it
- work has to be done against this force to push down the plunger and add more gas into the container
what is the effect of mechanically doing work with a bike pump against the gas in a container
- energy is mechanically transferred to the kinetic energy stores of the gas particles
- so it increases the internal energy ans therefore the temperature
we know that decreasing the volume of a container with the same number of gas particles increases the gas pressure due to the increase in the frequency of the collisions (ans that heating it up gives does the same thing with more force exerted on the container per particle.) But why does decreasing the volume increase the kinetic energy and temperature of the gas in itself?
- when you decrease the volume of the container, you are doing work on the gas, specifically, against the pressure of the gas
- this leads to the mechanical transfer of the chemical energy in your arms (eg) to the kinetic energy of your arms, which is then transferred to the kinetic energy stores of the gas particles
- this increase in kinetic energy is directly proportional to the temperature of the gas, so the temperature of the gas increases with this energy transfer
