Changing of state: Chemistry

Changing of state

Solid    ---Melting-->    Liquid     --Boiling/Evaporation-->     Gas
Solid    <--Freezing--    Liquid     <------Condensation------    Gas 
Solid    <-----------------Sublimation---------------------------------    Gas

Below melting point ----> Solid
Above melting point ---> Liquid
Below boiling point ----> Liquid
Above boiling point ----> Gas

--------Solid------->Melting Point<----------Liquid--------->Boiling Point<---------Gas---------

Matter
→Matter is anything that occupies space and mass.
→The Kinetic Partical Theory(KPT) states that all matter is made up of tiny particles and are always in constant,random motion.
→Matter can exist in three forms:
  -Solid
     ~Solid particles are arranged closely together in a fixed position.
     ~Solid particles can only vibrate gently about their fixed positions.
  -Liquid
     ~Liquid particles are closely packed together, although not as close as solid particles.

     ~Liquid particles can move a short distance, as they can slide past one another.

  -Gas

     ~Gas particles are far apart from each other.

     ~Gas particles can move about randomly.

→Matter's change in state is reversible.

I - Melting

→Melting is a process in which a solid changes into a liquid.

→Heat is absorbed during melting.

Q: What is melting point?

A: Melting point is the fixed temperature at which a substance melts.

→Different substances have different melting points.

Example:

Substance              Oxygen       Ice       Iron

Melting Point/°C    -219°C       0°C    1535°C

Interpretation of the graph

→On heating a solid, the particles absorb heat energy.

→Heat energy is converted into kinetic energy.

→The kinetic energy of particles increases and the particles vibrates faster and faster.

→At melting point,the particles have gained enough energy to overcome the attractive forces between the particles.

→Particles are able to move away from the fixed position and form a liquid.

→At the melting point, temperature remains constand because heat energy is being used to overcome the attractive forces between particles and seperate the particles(changing the solid to liquid).

II - Boiling

→Boiling is a process in which a liquid changes into a gas.

→This change in state occurs inside the liquid.

→Heat is absorbed during boiling.

Q:What is boiling point?

A:Boiling point is the fixed tempertature at which a substance boils.

→Different substances have different boiling points

Example:

Substance              Oxygen      Water       Iron

Boiling Point/°C    -183°C       100°C     3000°C

Interpretation of the graph

→On further heating, the kinetic energy of the particles increases further.

→The particles move faster and faster.

→At boiling point, particles have gained enough energy to completely overcome the attractive forces between particles and break free from one another.

→The particles escape the liquid and form a gas.

→At the boiling point, temperature remains constant because heat energy is needed to overcome the attractive forces between particles and seperate the particles(from liquid to gas)

III - Evaporation

→Evaporation is a process in which a liquid changes into gas.

→This change in state takes place at the surface of the liquid.

→Evaporation takes place at all temepratures below the boiling point of the liquid(when the substance is still in the liquid state)

Q:Can evaporation take place at the temperature below the melting point?

A:No.Below the melting point, the substance is a solid, hence it cannot evaporate as evaporation is a process where liquid changes to gas.(Solid to gas --> Sublimation)

→Liquids which evaporate quickly at low temperatures are called volatile liquids.

Example: Ethanol(alcohol),Perfumes

Note: Boiling and evaporation are not the same

Differences between boiling and evaporation:

                Boiling                                                  Evaporation

~Occurs only at boiling point                ~Occurs at temperatures below boiling point

~Takes place throughout the liquid       ~Takes place at the surface of the liquid

~Very fast process                              ~Very slow process

IV - Sublimation

→Sublimation is a process in which a solid changes into a gas without passing through the liquid phase.

→Heat is absorbed during sublimation.

Q: Does sublimation take place at a fixed temperature?

A: Yes. Examples: Dry ice(Solid CO²), iodine, ammonium chloride, mothballs

V - Condensation

→Condensation is a process in which a gas changes into liquid.

→This change in state occurs when a gas is cooled to its boiling point.

→Heat is evolved(released) during condensation.

→Condenstaion takes place at a fixed temperature numerically equal to its boiling point.