Kinetic Particle Theory Notes

States of Matter

• Matter: A substance that has mass and occupies space.
• Three states of matter:
  • Solid (e.g., ice)
  • Liquid (e.g., water)
  • Gas (e.g., water vapor)
• Properties of each state:
  • Solid:
    • Fixed shape
    • Fixed volume
    • Cannot be compressed
  • Liquid:
    • Not fixed shape
    • Fixed volume
    • Cannot be compressed
  • Gas:
    • Not fixed shape
    • Not fixed volume
    • Can be compressed

Kinetic Particle Theory

• Kinetic Particle Theory:
  • All matter is made up of tiny particles (atoms, molecules, or ions).
  • Particles are in constant and random motion.
  • Constant = non-stop, continuous.
  • Random = unpredictable.
  • The speed of particles depends on the amount of kinetic energy.
• Properties to consider in three states of matter:
  • Kinetic energy of particles.
  • Forces of attraction between particles.
  • Movement of particles.
  • Arrangement of particles.

Solid

• Arrangement of particles: Closely packed in an orderly manner.
• Movement of particles: Vibrate about fixed positions.
• Forces of attraction between particles: Very strong.
• Kinetic energy of particles: Low.
• Why solids have fixed shape and volume:
  • Particles are held together by very strong forces of attraction.
  • Particles vibrate about fixed positions and cannot move freely.
  • Particles are already very close together, so they cannot be compressed.

Liquid

• Arrangement of particles: Closely packed in a disorderly, random manner; slightly further apart than those of a solid.
• Movement of particles: Slide over each other.
• Forces of attraction between particles: Strong, but weaker than in a solid.
• Kinetic energy of particles: More kinetic energy than in a solid.
• Why liquids do not have a fixed shape but have a fixed volume:
  • Particles are arranged in a disorderly manner.
  • They have weaker forces of attraction compared to solids.
  • Particles are not held in fixed positions and can move freely throughout the liquid.
  • Particles are packed closely together.

Gas

• Arrangement of particles: Very far apart.
• Movement of particles: Randomly at high speeds in all directions.
• Forces of attraction between particles: Very weak.
• Kinetic energy of particles: A lot of kinetic energy.
• Why gases do not have a fixed shape or volume:
  • Particles are spread far apart from one another.
  • They have the weakest forces of attraction.
  • Particles have a lot of kinetic energy and are not held in fixed positions.
  • Particles can move about rapidly in any direction.
  • Gases can be compressed because there is space between the particles.

Summary Table

Changes in State of Matter and the Kinetic Particle Theory

• Matter can change from one state to another:
  • Melting: solid \rightarrow liquid
  • Freezing: liquid \rightarrow solid
  • Boiling: liquid \rightarrow gas (at boiling point)
  • Evaporation: liquid \rightarrow gas (at any temperature)
  • Condensation: gas \rightarrow liquid
  • Sublimation: solid \rightarrow gas
• Changes of state are reversible.

Melting

• Melting: The process by which a substance changes from a solid to a liquid.
• Process of melting:
  1. Particles gain kinetic energy and vibrate faster.
  2. Particles overcome attractive forces between them and break away from fixed positions.
  3. Particles now slide over one another. Solid has melted to liquid.
• Melting point: The temperature at which a solid melts.
• Temperature Changes in the Melting Process (Heating Curve):
  • A-B: As the solid is heated, particles in solid gain K.E., the temperature of the solid increases until it reaches point B, its melting point.
  • B-C: Melting occurs at a fixed temperature. Energy from heating is used to overcome forces of attraction between the particles. A mixture of solid and liquid exists. Particles do not gain K.E.
  • C-D: At point C, all the solid has melted. The temperature of the liquid rises as heating continues. Liquid particles gain K.E.

Freezing

• Freezing: The change from a liquid to a solid.
• When a liquid is cooled:
  1. Particles lose kinetic energy and move more slowly.
  2. Some particles start to settle into fixed positions.
  3. All the particles settle into fixed positions. Liquid has frozen into solid.
• Freezing point: The temperature at which a liquid freezes.
• Temperature Changes in the Freezing Process (Cooling Curve):
  • P-Q: Particles in liquid lose K.E. The temperature of the liquid drops to the freezing point, Q. At Q, the liquid starts to freeze.
  • Q-R: Liquid freezes. A mixture of liquid and solid exists. The temperature remains constant even though cooling continues.
  • R-S: Particles in solid lose K.E. At R, all the liquid has frozen. The temperature of the solid drops with further cooling.

Boiling

• Boiling: The change from a liquid to a gas at the boiling temperature.
• Boiling point: The temperature at which a liquid boils.
• Temperature Changes in the Boiling Process (Heating Curve):
  • W-X: Particles in liquid gain K.E., temperature of liquid increases until its boiling point, X, is reached.
  • X-Y: Liquid boils. A mixture of liquid and gas exists. The temperature of the liquid remains constant until all the liquid is boiled off.

Evaporation

• Evaporation: The change from a liquid to a gas below the boiling point.
• Particles have enough energy to escape as a gas from the surface of the liquid.
• Volatile liquids evaporate quickly at room temperature (e.g., perfume, petrol).

Differences Between Boiling and Evaporation

Condensation

• Condensation: The change from a gas to a liquid.
• Process:
  • Gas particles lose kinetic energy.
  • They move closer together.
  • An increase in attractive forces occurs.
  • Gas becomes liquid when temperature drops.

Sublimation

• Sublimation: The change from a solid to a gas without melting.
• The forces of attraction between particles in the liquid state are too weak to remain in this state.

Diffusion

• Diffusion: The process by which particles move freely to fill up any available space.
• Examples:
  • The scent of perfume spreads throughout a room.
  • The smell of spices from cooking spreads in a house.
  • An evidence of the kinetic particle theory.

Demonstrating Diffusion

• Place a gas jar of air over a gas jar containing bromine vapor. After removing the cover, the gas in both jars eventually looks the same.
• Explanation:
  • Both air and bromine consist of tiny particles moving randomly.
  • The bromine particles diffuse (spread out) into the spaces between the air particles, and vice versa.
  • A homogeneous mixture of air and bromine is formed.
  • When the gas looks the same in both gas jars, it means that the particles of both gases are evenly spread.
• Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

Rate of Diffusion

• Relative molecular mass (Mr): The mass of a gas particle.
• Gases with lower molecular masses diffuse faster than those with higher molecular masses.
• Smaller relative molecular mass = lighter gas = faster movement.
• Demonstration using ammonia and hydrochloric acid:
  • Set-up: Cotton wool soaked in concentrated ammonia solution at one end of a tube, and cotton wool soaked in concentrated hydrochloric acid at the other end.
  • Observation: White fumes of ammonium chloride form closer to the hydrochloric acid.
  • Explanation: The molecular mass of ammonia (Mr = 17) is lower than the molecular mass of hydrochloric acid (Mr = 36.5). Ammonia travels faster, so ammonium chloride is formed further from the ammonia solution.

Diffusion in Liquids

• A crystal of potassium manganate(VII) is introduced into a beaker of distilled water to show diffusion in liquids.
• A deep purple solution forms at the bottom of the beaker, and slowly diffuses until the solution becomes uniformly purple.

Effect of Temperature on the Rate of Diffusion

• When temperature increases, the rate of diffusion increases.
• If the diffusion of potassium manganate(VII) experiment were repeated using boiling water, the solution would become uniformly purple within a much shorter time.