STATES OF MATTER -
properties of gases and liquids (fluids) and solids
Condensation and distillation (state changes gas/vapour <=>
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
- 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 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
- The lowest kinetic energy molecules are most likely to condense first.
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
- 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!
- 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.
– the process of distilling a liquid
The process of distillation involves boiling (liquid ==>
gas/vapor) and the reverse process of condensation (gas/vapour ==> liquid)
Energy changes for these physical changes of state
for a range of substances are dealt with in a section of
the Energetics Notes
and also here in section 14.
of latent heat changes in physical changes of state for different substances
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
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
UK GCSE level (~US grade 8-10) school chemistry revision
All my UK advanced level (~US grades 11-12)
pre-university chemistry revision notes
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INDEX of all my notes on the states of matter
(GCSE level and advanced pre-university level
notes on the states of matter and their properties