ย 

Pressure for AQA A-level Physics

Pressure

This page covers the following topics:

1. Pressure in gases

The ideal gas equation relates pressure, volume, temperature and amount of gas. It is important to use the SI units of all the variables in the equation, the gas constant is 8.31 J Kโปยน molโปยน, one mole is Avogadro constant = 6.02 ร— 10ยฒยณ, the temperature needs to be given in kelvin (K). The absolute temperature in K can be found by adding 273.15 to the temperature in ยฐC.

There are three specific cases for the ideal gas equation. When only pressure and volume are changing, it is called Boyleโ€™s law and yields pโ‚Vโ‚ = pโ‚‚Vโ‚‚. When only pressure and temperature are changing, it is called Gay-Lussacโ€™s law and yields pโ‚/Tโ‚ = pโ‚‚/Tโ‚‚. When only volume and temperature are changing, it is called Charlesโ€™ law and yields Vโ‚/Tโ‚ = Vโ‚‚/Tโ‚‚.

Pressure in gases

1

16 moles of hydrogen occupy a volume of 5.2 dmยณ at a pressure of 112 kPa. Using the ideal gas equation, calculate the temperature in kelvins.

5.2 dmยณ = 0.0052 mยณ
112 kPa = 112000 Pa
pV = nRT
T = pV/nR
T = (112000 ร— 0.0052)/(16 ร— 8.31) = 4.38 K (3 s. f.)

4.38 K

16 moles of hydrogen occupy a volume of 5.2 dmยณ at a pressure of 112 kPa. Using the ideal gas equation, calculate the temperature in kelvins.

2

How many moles does a sample of gas with a volume of 0.57 mยณ at 101000 Pa and 300 K contain?

pV = nRT
n = pV/RT
n = (101000 ร— 0.57)/(8.31 ร— 300) = 23 mol (2 s. f.)

23 mol

How many moles does a sample of gas with a volume of 0.57 mยณ at 101000 Pa and 300 K contain?

3

Use the ideal gas equation and the information provided in the image to calculate how many molecules of the gas there are in the flask.

pV = nRT
n = pV/RT
n = (90000 ร— 0.045)/(8.31 ร— 312) = 1.56 mol (3 s. f.)

1.56 mol

Use the ideal gas equation and the information provided in the image to calculate how many molecules of the gas there are in the flask.

4

Provide and equation for Charlesโ€™ law that relates initial volume Vโ‚, initial temperature Tโ‚, final volume Vโ‚‚ and final temperature Tโ‚‚.

Charlesโ€™ law can be derived from the ideal gas law and yields Vโ‚/Tโ‚ = Vโ‚‚/Tโ‚‚.

Vโ‚/Tโ‚ = Vโ‚‚/Tโ‚‚

Provide and equation for Charlesโ€™ law that relates initial volume Vโ‚, initial temperature Tโ‚, final volume Vโ‚‚ and final temperature Tโ‚‚.

5

Using the ideal gas equation, calculate the volume of 2 moles of a gas at a temperature of 290 K and a pressure of 103000 Pa.

pV = nRT
V = nRT/p
V = (2 ร— 8.31 ร— 290)/103000 = 0.047 mยณ (2 s. f.)

0.047 mยณ

Using the ideal gas equation, calculate the volume of 2 moles of a gas at a temperature of 290 K and a pressure of 103000 Pa.

End of page

ย