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extra advanced notes on gas laws, ideal and non-ideal gasesSTATES OF MATTER - properties of gases and liquids (fluids) and solids

10. Condensation and distillation (state changes  gas/vapour <=> liquid)

Doc Brown's chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE  chemistry, O level and ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry and also helpful for UK advanced level chemistry students aged ~16-18 and US grades 11-12 K12 honors.


10a. Condensing (gas to liquid) – the process of condensation

Explained using the kinetic particle theory of gases and liquids

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  • On cooling, gas particles lose kinetic energy, they slow down and eventually become attracted together via intermolecular forces to form a liquid i.e. they haven't enough kinetic energy to remain free in the gaseous state.
  • There is an increase in order as the particles are much closer together and can form clumps of molecules.
    • The lowest kinetic energy molecules are most likely to condense first.
  • The process requires thermal energy (heat energy) to be lost to the surroundings i.e. heat given out, so condensation is exothermic (ΔH –ve in advanced level notation).
    • This is why steam has such a scalding effect, its not just hot, but you get extra heat transfer to your skin due to the exothermic condensation on your surface!
    • In your home you see condensation on cold windows and steam is invisible, and what you refer to as steam coming out of a kettle is actually a cloud of water droplets from the condensation of steam vapour in the cooler air.
  • Factors affecting the rate of condensation of a gas–vapour
    • The lower the temperature of the gas the faster it condenses because the particles on average have less kinetic energy to overcome the attractive intermolecular forces i.e. they gas particles are more likely to aggregate into drops of liquid.
    • The colder the surface the gas condenses on, the faster the heat transfer to reduce the kinetic energy of the gas particles, so the faster the gas/vapour can condense.
    • The higher the concentration of vapour in air, the faster condensation can take place. The particles are closer together and more chance of colliding and combining to form liquid droplets.


10b. Distillation – the process of distilling a liquid


Learning objectives for the state change of condensation

Know what we mean by condensation - the sate change from gas/vapour to liquid.

Be able to use the kinetic particle theory of matter to explain the state of matter change of condensation

Know that particles in a gas/vapor have a wide variety of speeds (velocities) and kinetic energies.

Know that lowest kinetic energy molecules condense first.

Know that thermal energy is released by the gas as it condenses - exothermic processes.

Know that distillation involves boiling followed by condensation and the state changes are liquid ==> gas/vapour ==> liquid


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INDEX of all my notes on the states of matter

(GCSE level and advanced pre-university level revision notes)

Detailed notes on the states of matter and their properties

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