weirdfacts
Year 11 / Intermolecular forces and gases

Pressure comes from collisions.

The ideal-gas model assumes negligible particle volume and intermolecular attractions, with elastic collisions. Pressure results from particles colliding with container walls. Raising absolute temperature increases mean kinetic energy, affecting collision frequency and momentum transfer.

At fixed amount and temperature, pressure varies inversely with volume. At fixed amount and volume, pressure is proportional to kelvin temperature. Choose units consistent with R: kPa and litres can be used with 8.314 kPa L mol⁻¹ K−1K^{-1}. Real gases depart most strongly from ideal behaviour at high pressure or low temperature.

INTERACTIVE MODEL

Compress an ideal gas

Pressure / kPa: 499 · schematic
READ THE GRAPH

Explore the relationship

1.00 mol ideal gas; R = 8.314 kPa L mol⁻¹ K⁻¹. Use absolute temperature.

Pressure / kPa0130.9261.9392.8523.8511.2517.523.7530Volume / L
Pressure / kPa

Tap or focus a plotted point to read its values.

View plotted data as a table
Explore the relationship
SeriesVolume / LPressure / kPa
Pressure / kPa5498.84
Pressure / kPa5.41667460.468
Pressure / kPa5.83333427.577
Pressure / kPa6.25399.072
Pressure / kPa6.66667374.13
Pressure / kPa7.08333352.122
Pressure / kPa7.5332.56
Pressure / kPa7.91667315.057
Pressure / kPa8.33333299.304
Pressure / kPa8.75285.051
Pressure / kPa9.16667272.095
Pressure / kPa9.58333260.264
Pressure / kPa10249.42
Pressure / kPa10.4167239.443
Pressure / kPa10.8333230.234
Pressure / kPa11.25221.707
Pressure / kPa11.6667213.789
Pressure / kPa12.0833206.417
Pressure / kPa12.5199.536
Pressure / kPa12.9167193.099
Pressure / kPa13.3333187.065
Pressure / kPa13.75181.396
Pressure / kPa14.1667176.061
Pressure / kPa14.5833171.031
Pressure / kPa15166.28
Pressure / kPa15.4167161.786
Pressure / kPa15.8333157.528
Pressure / kPa16.25153.489
Pressure / kPa16.6667149.652
Pressure / kPa17.0833146.002
Pressure / kPa17.5142.526
Pressure / kPa17.9167139.211
Pressure / kPa18.3333136.047
Pressure / kPa18.75133.024
Pressure / kPa19.1667130.132
Pressure / kPa19.5833127.363
Pressure / kPa20124.71
Pressure / kPa20.4167122.165
Pressure / kPa20.8333119.722
Pressure / kPa21.25117.374
Pressure / kPa21.6667115.117
Pressure / kPa22.0833112.945
Pressure / kPa22.5110.853
Pressure / kPa22.9167108.838
Pressure / kPa23.3333106.894
Pressure / kPa23.75105.019
Pressure / kPa24.1667103.208
Pressure / kPa24.5833101.459
Pressure / kPa2599.768
Pressure / kPa25.416798.1325
Pressure / kPa25.833396.5497
Pressure / kPa26.2595.0171
Pressure / kPa26.666793.5325
Pressure / kPa27.083392.0935
Pressure / kPa27.590.6982
Pressure / kPa27.916789.3445
Pressure / kPa28.333388.0306
Pressure / kPa28.7586.7548
Pressure / kPa29.166785.5154
Pressure / kPa29.583384.311
Pressure / kPa3083.14
Pressure / kPa: 498.84

Explore: Halve volume at fixed temperature, then raise the kelvin temperature.

PV=nRTPV=nRT
WORKED EXAMPLE

Find pressure of 1.00 mol ideal gas in 24.0 L at 300 K; R = 8.314 kPa L mol⁻¹ K−1K^{-1}.

  1. P = nRT/V.
  2. P = 1.00 × 8.314 × 30024.0\frac{300}{24.0} = 104 kPa.
Assumed knowledge

Moles and temperature conversion.

Learning checkpoints & sourceYOUR LEARNING CHECKPOINT
  • Explain gas behaviour using kinetic theory.
  • Use PV = nRT with consistent units.
QCAA Chemistry · Unit 2 · Intermolecular forces and gases ↗
READY TO TRY IT?

Put the idea to work.

Back to syllabusNext: Concentration counts amount per volume.
Loading progress…