Wednesday, 8 April 2009

iGCSE Chemistry - Physical Chemistry

States of Matter

 

  • There are three states of matter: gas, liquid, and solid
  • In gases, particles are far apart from each other and expand to fill a space.
  • In liquids, particles are held together but have energy to move around, and thus have no definite shape
  • In solids, particles are held in a fixed position and thus solids have a definite shape.
  • In mixtures, individual substances can be separated through physical means. The chemical properties are the same as the components’.
  • In compounds, the components can only be separated by chemical means. The chemical properties different to the components’.
  • Distillation is used to separate mixtures of two or more liquids by relying on the fact that they have different boiling points.
  • Fractional distillation is used to refine oil and involves a fractionating column which separates the mixture into “fractions”.
  • Filtration separates a liquid from a solid using filter paper.
  • Crystallisation involves evaporating the liquid in a solution to leave crystals.
  • Paper chromatography separates mixtures of several soluble solids. The different solids have different solubilities and thus move at different speeds across the paper.

 

 

Acidity, Alkalinity and Neutralisation

 

Colour of litmus

Type of solution

Red

Acidic

Purple

Neutral

Blue

Alkaline

 

  • Phenolphthalein indicator is colourless in acid and pink in alkaline.
  • Methyl orange indicator is pink in acid and yellow in alkaline.
  • Universal indicator: Brick = Acid, Green = Neutral, Blue = Alkaline
  • pH scale is 1-14, 1 being acid and 14 being alkali. 7 is neutral.
  • Acids lose protons in reactions

 

Salt equations

Acid + Alkali -> Salt + water

Acid + Base -> Salt + water

Acid + Carbonate -> Salt + water + CO2

Acid + Metal -> Salt + hydrogen

 

 

Energetics

 

  • Reactions in which the temperature is increased are exothermic
  • Reactions in which the temperature is decreased are endothermic
  • Energy changes occur when bonds are made or broken
  • Enthalpy is the heat energy in chemical equations
  • Enthalpy change: Mass x heat capacity x rise in temperature
  • No energy can be created or destroyed, and thus the enthalpy change comes from the chemical reaction
  • In exothermic reactions, enthalpy change is negative, as energy is given out to the surroundings.
  • In endothermic reactions, enthalpy change is positive, as energy is taken in from the surroundings.
  • Breaking bonds is endothermic and creating bonds is exothermic.

 

Rates of Reaction

 

  • Increased surface area increases the rate of reaction.
  • Increased concentration increases the rate of reaction.
  • Increased temperature increases the rate of reaction.
  • Use of a catalyst increases the rate of reaction.

 

Equilibria

 

  • Equilibrium can only occur in reversible reactions.
  • Equilibrium is affected by concentration, temperature, and pressure.
  • Le Chatalier’s principle states that when a variable such as temperature is changed, the equilibrium will shift to counteract that change.

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