Pressure and Temperature
Introduction
In this title we are going to explore how temperature affects the pressure exerted by a gas.
We are going to do this by looking at a scenario of a volume of gas in a container above a Bunsen burner.
Finally, we will look at a GCSE exam question where we can apply what we have learned.
In the centre you will see the container of gas on a tripod above a Bunsen burner.
Three dials allow you to monitor properties of the gas.
At the top is the pressure in kilo Pascals. On the right is a thermometer giving the temperature in degrees Kelvin. The gas starts at room temperature of 20.0oC, this is 293⁰K.
On the left is an indication of the number of collisions made by the molecules of the gas.
This is only counting the collisions of the molecules seen here in yellow. In reality, there is a huge number of molecules in such a volume, but this number will be sufficient for us to see how the molecules behave in reality.
You should be seeing the molecules moving around at a moderate speed, they hit each other and the sides of the container. It is this striking of the sides of the container that is the cause of the pressure.
Applying heat
Without applying any heat, the pressure is at normal atmospheric value of 293 kPa and the temperature is room temperature, indicated on the wall thermometer to the left of the scene.
You should notice that the collision rate varies considerably. This is due to the low number of molecules represented here. However, the pressure reading is what we would get from the actual gas with its huge number of molecules which averages out the variation completely.
Light the Bunsen burner by clicking on the gas tap and watch the dials.
As the temperature rises, the pressure will rise, and the rate of the collisions will also rise.
You should be able to observe the molecules moving at a greater velocity, this means they have more momentum and when they strike the sides of the container they create more pressure, hence the increased reading on the top dial.
Pressure and Temperature
For a range of temperatures, say from 300 to 600 ⁰K in steps of 30 ⁰K :
•Record the pressure;
Create a graph of temperature on the x-axis and pressure on the y-axis.
You should find a straight-line or linear relationship between the temperature and the pressure.
Pressure and Collision Rate
For the same range of temperatures:
•Record the number of collisions;
Create a graph of the temperature on the x-axis and square of the collision rate on the y-axis.
You should find a linear relationship between the temperature and the square of the collision rate. However, it unlikely to be a very good fit due to the random nature of the collisions. To get a better fit take 3-5 readings of the collision rate at each temperature and take the average.
Exam Questions
AQA May 25 Foundation Paper 1
If you have difficulty answering this, try the e-scenario again taking note of how the particles move when you heat the volume of gas.
Remember that kinetic energy is related to the speed of the particles by:
KE = 0.5mV²
So that if V increases then so does the kinetic energy.
If you have difficulty answering this, try the e-scenario again taking note of the rate of the collisions when you heat the gas.
Consider the effect on the wall of a particle hitting at a low speed and one hitting at a high speed.