STPM Chemistry Form 6 Notes – Terminology and Concepts: Liquid and Solid States (Part 1)

by BerryBerryTeacher

in Berry Reference (Notes)

Continuing from the previous post about Gas, Berry Berry Easy will be releasing a series of notes about “Liquid and Solid State“. This topic will be longer but should be slightly easier than gas. Most of this topic would seemed as very common and just reinforces what you have already known from daily life. This could be due to the fact that you can ‘feel’ liquid and solid state matter with your fingers and see it more easily than gases. So let us begin the journey to this relatively easy topic. (Note however that, some students still make silly mistakes which meant that they concede easy marks away)

STPM Form 6 – Terminology and Concepts: Liquid and Solid States (Part 1)

Changes in the States of Matter

  1. Freezing / Solidification – liquid –> solid
  2. Melting – solid –> liquid
  3. Evaporation – liquid –> gas / vapour
  4. Condensation – gas / vapour –> liquid
  5. Sublimation – gas / vapour –> solid
  6. Sublimation – solid –> gas / vapour

(Sublimation – iodine, ammonium chloride and solid carbon dioxide)

Kinetics Theory of Liquid

The kinetics energy content of the particles in a liquid is closer to the kinetic energy content of the particles in a solid than to that of a gas.

Important points:

i) Liquid is made up of tiny particles.
ii) Particles in liquid are continually moving in a zigzag.
iii) The motion for particles in liquid are vibration, rotation and translation.
iv) Particles in liquid are not in an orderly arrangement. There are loose clusters of particles which are packed closely.
v) Particles in liquid have strong forces of attraction between the particles.
vi) Particles in liquid have more kinetic energy than the particles in solid but less kinetic energy than particles in gases.

Enthalpy of Fusion – The amount of heat required to change one mole of a pure solid into a liquid.

Enthalpy of Vaporisation – The amount of heat required to change one mole of pure liquid into a gas.

The Structure of a Liquid

i) Melting process:

  • Particles move faster when solid is heated.
  • The vibrations of the particles increase when temperature of the hot solid increases.
  • The particles in the solid acquired sufficient kinetic energy to overcome the attraction forces between particles.
  • The particles break away from one another.
  • Solid has become liquid.

ii) Freezing process:

  • The motion of particles in liquid slows down when liquid is cooled.
  • The particles have low kinetic energy.
  • The particles in liquid have strong attraction forces between particles to overcome the motion of the particles.
  • Particles held in fixed positions in the lattice structure.
  • Liquid has become solid.

iii) Vaporisation process (open container that exposed to the atmosphere):

  • The particles escape from the surface of the liquid and become gas.
  • The rate of vaporisation increases with a rise in temperature, a decrease in external pressure and an increase in the surface area of the liquid.
  • A rise in temperature
  • - room temperature: small percentage of particles have high kinetics and sufficient to overcome the attraction forces between particles and then escape from the surface of the liquid.

    A decrease in external pressure (increase in internal pressure)
    - particles that have enough kinetics energy to vaporise.
    - vapour pressure of liquid increases.
    - the particles in liquid collided with one another.
    - particles have enough kinetics energy to vaporise.
    - a distribution of kinetic energy has formed.

    An increase in the surface area of the liquid
    - the particles in liquid are collided with one another.
    - liquid exposed to the air will evaporate (on top of the liquid).
    - particles with higher kinetics energies than the average kinetic energy will escape as gas particles first.

iv) Boiling process:

  • Particles move faster when liquid is heated.
  • The vibrations of the particles increase when temperature of the hot liquid increases.
  • The particles in the solid acquired sufficient kinetic energy to overcome the attraction forces between particles.
  • The particles break away from one another.
  • Solid has become liquid.

Velocity of the particle ­ increase when

  • Temperature ­increase
  • Kinetic energy ­increase

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