Gas Temperature and Pressure Quiz

What is temperature and what are the units?

Temperature is a measure of the average kinetic energy of particles and it is measured in one of two units; degrees Celsius (˚C) and degrees Kelvin (˚K).

Degrees Celsius (˚C) and degrees Kelvin (˚K) are on the same scale, just shifted by 273˚C. This means that 1˚C and 1˚K are the same size interval.

To change between these units either subtract or add 273.

From Kelvin to Celsius: subtract 273.

From Celsius to Kelvin: add 273.

Since temperature measures particle motion, there is a minimum possible temperature at which all particles stop moving. This is called absolute zero and is 0˚K and -273˚C.

What is pressure and how do we measure it?
Pressure is caused by moving particles colliding with the walls of the container; the more collisions, the higher the pressure.
Pressure is measured in units called Pascals (Pa) and 1 Pa = 1 N/m². 

Since all forces are measured in Newtons (N) and particles colliding cause a surface to experience a force, we combine the units for force (N) and pressure (m²) to get N/m² and 1 N/m² = 1 Pa.

Atmospheric pressure –

At sea level on Earth, the air in the atmosphere above and around you exerts a pressure of 101,235 Pa.

This pressure can affect the state of matter. At very low pressures, such as in space, solids can turn directly into gases through a process called sublimation. Similarly, at extremely high pressures, gases can turn directly into solids, a process called deposition.

Pressure example 1 – a flexible container:

A balloon expands as it is filled with air because collisions of air particles with the walls of the balloon are more frequent inside than outside. When the forces become balanced, the balloon stops inflating.

In this case, the forces involved are; pressure from air particles inside the balloon, the pressure from air particles outside the balloon, and the elastic force of the balloon material, which counteracts the pressure inside.

Pressure example 2 – an inflexible container:

Adding CO² to a fire extinguisher will not affect the size of the container because it is inflexible. Pressure will increase inside the container.

For Separate Science (Physics) you also need to understand the following points:

• Gases can be compressed or expanded by pressure changes.
• The pressure of a gas produces a net force at right angles to any surface.
• Changing the volume of a gas affects the rate of particle collisions with the container walls, and thus the pressure, for a fixed mass of gas at constant temperature.
• Use the equation to calculate pressure or volume for gases of fixed mass at constant temperature:

$$ P_1 \times V_1 = P_2 \times V_2 $$