C6: Chemical reactions

  1. Physical and chemical changes

  • Physical:

    • Substances present remain chemically the same

    • Easy to reverse → mixtures are easy to separate

    • Involve heat energy → taken in/given out

  • Chemical:

    • Result of chemical reactions

    • New substances are made

    • Many (not all) are difficult to reverse

    • An exothermic/endothermic can occur

  1. Rate of reaction

  • Factors that influence reaction rate:

    • Surface area: more surface area = more places for particles to collide

    • Concentration: more particles = higher chance of collision

    • Pressure of gases: more pressure = less volume for particles to move in → higher chance of collsion

    • Temperature: more kinetic energy = particles move faster

    • Catalyst: speeds up the reaction while remaining unchanged by reducing the amount of energy needed to break bonds

  1. Redox reactions

  • Combustion, oxidation and reduction

    • Combustion: substance being combusted it oxidized

    • Oxidation: substance gains oxygen

    • Reduction: substance loses oxygen

    • oxidation and reduction are simultaneous→ redox

  • Oxidation numbers: shown by roman numerals in transition metals

    • Oxidation number increases → oxidized

    • Oxidation number decreases → reduced

  • Electron loss and gain in redox reactions

    • Oxidation: loss of electrons

    • Reduction: gain of electrons