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STATES OF MATTER - properties of gases and liquids (fluids) and solids

8. A summary diagram of state changes

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.


Changes of State for gas <=> liquid <=> solid

You need to be able to predict the state of a substance at different temperatures given appropriate data.

Below its melting point a substance is a solid.

Between its melting point and boiling point, the substance is a liquid.

(however, note that there will always some vapour above a liquid with an exposed surface)

Above its boiling point, a substance is a gas/vapour (vapor).

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FREEZING

MELTING

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SUBLIMING - the opposite is deposition or 'reverse sublimation'

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BOILING or EVAPORATING

SUMMARY of the CHANGES of STATE between a gas, liquid and solid

All mass conserved in these PHYSICAL CHANGES

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CONDENSING

These are NOT chemical changes !

A change of state means an interconversion between two states of matter,

usually the interchange of states: gas <=> liquid <=> solid

A 'triangular' summary of important state changes is illustrated above.

e.g. solid ==> liquid is melting or fusing - thermal energy absorbing - endothermic

liquid ==> gas/vapour (vapor) is boiling, evaporation or vapourisation (vaporisation, vaporization, vapourization) - thermal energy absorbing - endothermic

and the reverse processes

gas/vapour (vapor) ==> liquid is condensation, liquefaction or liquefying (the latter often done under pressure) - thermal energy releasing - exothermic

liquid ==> solid is freezing, solidifying or crystallising - thermal energy releasing - exothermic

and there is also the 'special' case of sublimation, where the liquid state is 'bypassed'.

solid ==> gas is sublimation, with no intermediate liquid state (endothermic process).

The reverse process i.e.  gas ==> solid is sometimes referred to as deposition or reverse sublimation

We can use the state particle models and diagrams to explain changes of state and the energy changes involved. See sections 9 to 13 from the index

These are NOT chemical changes BUT PHYSICAL CHANGES

e.g. the water molecules H2O are just the same in ice, liquid water, steam or water vapour.

What is different, is how the water particles are arranged, and how strongly they are held together by intermolecular bonding forces in the solid, liquid and gaseous states.

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.

14. Comparison of latent heat changes in physical changes of state for different substances


Learning objectives from the summary of state changes defined and illustrated above.

Be able to predict the state of a substance at different temperatures given appropriate data i.e. below its melting point a substance is a solid, between its melting point and boiling point, the substance is a liquid and above its boiling point a substance is a gas or vapour.

Be able to define and know the physical state changes for melting, boiling, evaporation, condensing, freezing, liquefaction, crystallising (crystallizing) and subliming.

Know and be able to explain that state changes are physical changes and NOT chemical changes, no new substances are formed, the chemical composition of the material is unchanged BUT total mass is conserved i.e. no loss or gain of mass..

Know that the identical particles of a pure substance particles are arranged differently and their physical state depends on how strongly the particles are held together by chemical bonding or the weaker  intermolecular bonding forces in the solid, liquid and gaseous/vapour states.


All my UK GCSE level (~US grade 8-10) school chemistry revision notes

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 revision notes)

Detailed notes on the states of matter and their properties

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