Gas volume, temperature and particle collisions

Gas volume, temperature and particle collisions

Gas pressure comes from particle collisions with container walls. At constant amount of gas, increasing temperature increases the average kinetic energy of particles; at constant volume this makes collisions more frequent and forceful, increasing pressure. At constant pressure, a hotter gas expands. Chemical gas calculations require an absolute temperature scale, so convert degrees Celsius to kelvin by adding 273. For Grade 11 work, keep conditions explicit: gas volume depends on temperature and pressure, and the molar volume at room temperature and pressure is commonly taken as 24 dm³ mol⁻¹. An ideal-gas model is useful, but real gases deviate most at high pressure and low temperature.

Work it through

A sample at 27 °C must be recorded as 300 K before using a temperature ratio. If 0.50 mol of a gas is measured at RTP, use V = n × 24 dm³ mol⁻¹: V = 0.50 × 24 = 12 dm³. Write the condition beside the value so an examiner can see why 24 dm³ mol⁻¹ was used.

Mastery target

Convert temperature correctly, relate a collision model to pressure or volume, and calculate a gas volume at stated conditions.