Datalogging in Science

Pressure v Temperature

How does the pressure of a gas affect its temperature?
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Overview

In this demonstration, a fixed mass of gas is heated. While its tendency is to expand, the pressure on the gas is increased as the temperature increases so that the volume occupied by the gas remains constant. The pressure and temperature are recorded in Real time as the gas is heated. Thus the relationship between pressure and temperature becomes apparent from viewing the graph as it develops.


Theory

The Gas laws (of Boyle and Charles) relate the quantities of pressure temperature and volume of a gas.
This demonstration looks at the third permutation where the volume of gas is kept constant.

Apparatus

1. Heat Source,
2. Beaker,
3. Test Tube with rubber bung,
4. Retort stand & clamp,
5. Datalogger,
6. Pressure Sensor,
7. Temperature Sensor.

(N.B. A constant Volume gas thermometer is ideal for this demonstration, but the following apparatus will also serve.)

Procedure

1. Set up the apparatus in a similar way to that shown.


2. Connect the Pressure Sensor and Temperature sensor to the
datalogger.

3. Connect the datalogger to the computer.

4. Launch the Graph software and set it to record in Real time and to plot Pressure against Temperature.

5. Begin heating the water and begin recording.

6. Continue heating and recording until the water nearly boils.

7. Switch off the heat and stop recording.

Results

A graph develops on the computer screen according as the heating proceeds.

Remember to save your work to the recommended folder. Print a copy of the graph for review purposes.


Questions

From analysis of the graph what is the nature of the relationship between pressure and temperature for a fixed volume of gas?

Extensions

1. Investigate how pressure and temperature are related while the water cools down to room temperature.
What conclusions can be drawn from the outcome?


2. Convert the pressure sensor readings to gas pressures by adding the atmospheric pressure to each of the readings taken. Convert the temperature sensor readings to absolute temperatures by adding 273 K to each of the readings taken. Now plot gas pressure versus absolute temperature. Analyse the graph to see where it crosses the axis.


3. What conclusion can you draw?


4. What might be the outcome if a gas other than air was used?

Footnote


Pressure is defined as force per unit area. It is measured in Pascals (where one pascal is the pressure resulting from a force of one Newton per meter squared.
Pressure is a scalar quantity. Although the relationship established here can be derived from the ideal gas equation, it is an experimentally verifiable relationship (first shown by Gay Lussac in 1802)

Data Harvest users

1. Connect the sensor to the datalogger and the logger to the computer
2. Then click the Set Up icon to the right of this message.
3. When the software opens, click the Play button.