Chemistry Notes Form 3

Chemistry Notes Form 3

Chemistry Notes Form 3

Gas Laws

Kinetic Particle Theory

 

  • Matter is made up of particles that are in constant motion
  • The higher the temperature, the faster the particles move (more energy)
  • Increase in temperature increase weakens interparticle forces, causing particles to spread apart and increase in volume/size (i.e. Expansion)
  • Gases have greatest average energy while solids have smallest average energyAccording to the kinetic theory, matter is made up of particles (atoms, molecules or ions) which are in constant motion because they have energy at all temperatures above zero Kelvin (absolute zero, 0K) or -2730C.This energy is in the form of kinetic energy.

    Consider heating a solid;

    When a solid is heated, the particles vibrate more strongly as they gain kinetic energy and the particle attractive forces are weakened.

    Eventually, at the melting point, the attractive forces are too weak to hold the particles in the structure together in an ordered way and so the solid melts.

    The particles become free to move around and lose their ordered arrangement.

    Energy is needed to overcome the attractive forces and give the particles increased kinetic energy of vibration.

    On heating further, the particles gain more kinetic energy and move faster.

    In evaporation and boiling the particles with the highest kinetic energy can ‘escape’ from the attractive forces of the other liquid particles.

    The particles lose any order and become completely free to form a gas or vapour.

    Boiling is rapid evaporation anywhere in the bulk liquid and at a fixed temperature called the boiling point and requires continuous addition of heat.

    Diffusion and Kinetic Energy

    The natural rapid and random movement of the particles means that gases readily ‘spread’ or diffuse

    Diffusion is the movement of gas or solid particles from a region of high concentration to a region of low concentration

     

    Diffusion is fastest in gases where there is more space for them to move

    The rate of diffusion increases with increase in temperature as the particles gain kinetic energy and move faster

    Diffusion of Ammonia and Hydrogen Chloride

    The following experiment is set up

    One filter soaked in a solution of ammonia solution and the other soaked in a solution of concentrated hydrochloric acid are placed on the end of along glass tubing as shown

     

    When colourless NH3 and HCl fumes meet, dense white smoke (fumes) of ammonium chloride are observedNH3 (ag) + HCl (ag) -> NH4 Cl(s)

    Ammonia is diffused more rapidly than the hydrogen chloride because the gas traveled a longer distance in the same amount of time

    Gases with greater R.M.M have higher densities than gases which have small molecules eg. hydrogen chloride are heavier than ammonia molecules

    If the concentration of hydrochloric acid and that of ammonia were increased in a separate experiment, the rate of diffusion would be faster

    Gas Mr

    NH3 17

    HCl 35

    5 Large heavy molecules move more slowly than small, light molecules

    Therefore, dense gases diffuse more slowly than gases of low density

    The rate of diffusion depends on the molecular mass/density of gas

    Rate of diffusion is inversely proportional to mass of a gas

    Rate of Diffusion;

     

  • Increases with temperature
  • Decreases with increasing R.M.M or R.A.M
  • Increases with concentrationGraham’s Law of DiffusionGraham’s law of diffusion relates the rate of diffusion of a gas to its density

    It states that the rate of diffusion of a gas at constant temperature and pressure is inversely proportional to the square root of its density

     

    Evaporation, boiling and kinetic theoryOn heating particles gain kinetic energy and move faster

    In evaporation and boiling the highest kinetic energy molecules can ‘escape’ from the attractive forces of the other liquid particles

    The particles lose any order and become completely free to form a gas or vapour

    Energy is needed to overcome the attractive forces in the liquid and is taken in from the surroundings

    This means heat is taken in, so evaporation or boiling are endothermic (require energy input) processes

    If the temperature is high enough boiling takes place

    Boiling is rapid evaporation anywhere in the bulk liquid and at a fixed temperature called the boiling point and requires continuous addition of heat

    The rate of boiling is limited by the rate of heat transfer into the liquid

    Evaporation takes place more slowly at any temperature between the melting point and boiling point, and only from the surface, and results in the liquid becoming cooler due to loss of higher kinetic energy particles

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