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*[[Evaporating]] is when a liquid turns into a gas.
*[[Condensing]] is when a gas turns into a liquid.
==Key Stage 3==
===Meaning===
[[File:ParticleModelStateChanges.png|right|300px|thumb|This diagram shows the '''changes of state''' between the three [[State of Matter|states of matter]].]]
A '''state change''' is when a [[substance]] changes from one [[State of Matter|state of matter]] to another.
===About State Changes===
: A [[State of Matter|state of matter]] can change if the [[temperature]] changes.
*[[Melting]] is when [[solid]] turns into a [[liquid]].
*[[Freezing]] is when a [[liquid]] turns into a [[solid]].
*[[Evaporating]] is when a [[liquid]] turns into a [[gas]].
*[[Condensing]] is when a [[gas]] turns into a [[liquid]].
*[[Subliming]] is when a [[solid]] turns into a [[gas]].
*[[Depositing]] is when a [[gas]] turns into a [[solid]].
===Energy and State Changes===
: '''Changing state''' either needs [[energy]] to happen or releases stored [[energy]] when it happens.
{| class="wikitable"
|-
|[[File:EnergyStateChanges.png|center|500px]]
|-
| style="height:20px; width:200px; text-align:center;" |When [[energy]] is added by [[heat]]ing a [[solid]] will turn into a [[liquid]] and then a [[liquid]] will turn into a [[gas]]. When [[energy]] is taken away by cooling a [[gas]] will turn into a [[liquid]] and a [[liquid]] will turn into a [[solid]].
|}
*[[Melting]], [[Evaporating]] and [[Subliming]] are [[endothermic]] changes because they need [[energy]] to happen. The [[material]] has more [[energy]] at the end than it did the beginning.
: When a [[solid]] [[melting|melts]] [[energy]] is needed to break the [[bond]]s holding the [[particle]]s in fixed positions.
: When a [[liquid]] [[evaporating|evaporates]] [[energy]] is needed to break the [[bond]]s that keep the [[particle]]s together.
: When a [[solid]] [[subliming|sublimates]] [[energy]] is needed to break the [[bond]]s holding the [[particle]]s in fixed positions and keeping the [[particle]]s together.
*[[Freezing]], [[Condensing]] and [[Depositing]] are [[exothermic]] changes because it releases [[energy]] when it happens. The [[material]] has less after it has happened.
: When a [[gas]] [[condensing|condenses]] [[energy]] is released as [[bond]]s form between adjacent [[molecule]]s to hold them together.
: When a [[liquid]] [[freezing|freezes]] [[energy]] is released as [[bond]]s form between adjacent [[molecule]]s to keep them in fixed positions.
: When a [[gas]] [[depositing|deposits]] [[energy]] is released as [[bond]]s form between adjacent [[molecule]]s to hold them together and keep them in fixed positions.
: When [[human]]s [[sweat]] the [[water]] [[evaporation|evaporates]] from the [[skin]] helping them cool down. This works because [[evaporation]] is an [[endothermic]] process so the [[sweat]] takes [[energy]] away from the [[skin]] when it [[evaporation|evaporates]].
==Key Stage 4==
===Meaning===
A '''state change''' is a [[Physical Change|physical change]] in which a [[substance]] turns from one [[State of Matter|state of matter]] into to another.
===About State Changes===
: '''State changes''' are [[reversible]] because after a '''state change''' the [[material]] can be returned to its original form with the same [[property|properties]] as it started with.
: '''State changes''' happen when a [[substance]] gains enough [[energy]] to break the [[bond]]s holding [[particle]]s together or loses enough [[energy]] for [[bond]]s to form between [[particle]]s.
: When the [[bond]]s between [[particle]]s in a [[solid]] or a [[liquid]] are broken the [[particle]]s gain [[Potential Energy|potential energy]]. This is an [[endothermic]] process because it needs [[energy]].
: When [[bond]]s are formed between [[particle]]s in a [[gas]] or a [[liquid]] the [[particle]]s lose [[Potential Energy|potential energy]]. This is an [[exothermic]] process because [[energy]] is given off.
====Edexcel====
:[https://www.amazon.co.uk/gp/product/1292120215/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1292120215&linkCode=as2&tag=nrjc-21&linkId=8f96ddb76196848bafdb124354e4cf77 ''State changes, page 3, GCSE Chemistry, Pearson, Edexcel '']