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• The key features of a chemical reaction are:

  • Compounds are broken up or formed
  • At least 1 new substance is created
• The key features of a chemical reaction are:

  • Compounds are broken up or formed
  • At least 1 new substance is created
• The key features of a chemical reaction are:

  • Compounds are broken up or formed
  • At least 1 new substance is created
  • Measurable energy change
  • No atoms are created or destroyed
• • State symbols
  • (s)
  • Solid
  • (l)
  • Pure liquid
  • (aq)
  • Aqueous solution
  • (g)
  • Gas
• The Law of Conservation of Mass

  Total mass of reactants = Total mass of products
• Changing Mass

  Burning of wood

  • When wood is burnt, it releases carbon dioxide and water (and often other gases).
  • These gases can escape into the atmosphere. These gases can't be weighed easily at the end of a reaction.
• Changing Mass

  Corrosion of metals

  • The mass of the oxide produced will be larger than the mass of the starting metals because oxygen atoms from the atmosphere have been added
  • The change in mass will equal the mass of the oxygen atoms which have been added
• Substances can seem to lose or gain mass when they react. This is usually because a reactant or product is a gas.
• Moles

  Individual atoms

  • Because atoms and molecules are so small, it is inconvenient to talk about individual atoms.
  • Instead, chemical amounts can be measured in moles.
• Moles

  • 1 mole of any substance is 6.02x1023 atoms of that substance.
  • This number is called the Avogadro constant.
• Limiting Reactant

  The reactant that is completely used up is called the limiting reactant because the reaction stops when it is used up.
• A reactant that is completely used up in a reaction is called the limiting reactant.
• Endothermic Reactions

  • Energy from the surroundings is transferred to the reacting chemicals, causing the temperature of the surroundings to decrease. Examples include:
  • Thermal decomposition.
• Exothermic reactions

  • Energy from the reacting chemicals is transferred to the surroundings, which often increase in temperature as a result. Examples include:
  • Combustion.
  • Neutralisation.
  • Oxidation.
• In chemical reactions, energy can't be created or destroyed. We say that energy is conserved.
• Bond making = exothermic

  Bond breaking = endothermic
• Calculate the energy change in a reaction by subtracting the total bond energies of products from the total bond energies of reactants.
• There are 2 main requirements for a successful reaction to take place:

  Collisions

  • Particles of the reactants have to collide.

  Activation energy

  • The collisions that happen between particles of the reactants must take place with enough energy.
  • This threshold amount of energy is called the activation energy.
• Exothermic

  
• Endothermic

  
• Catalysts can increase reaction rates by lowering the activation energy, which increases the likelihood of successful collisions.
• Catalysts decrease activation energy
• Activation energy is the minimum amount of energy required for a reaction to occur.
• Oxidation

  Is

  Loss of electrons (more positive)

  Reduction

  Is

  Gain of electrons (more negative)
• Oxidation reaction is when metals react with oxygen to form metal oxides.
• Redox reactions involve a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons).
• Acids are substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions).
• Alkalis are substances that form hydroxide (OH-) ions when they dissolve in water (aqueous solutions). An alkali is a type of base.
• Litmus Paper

  Acidic - Red

  Neutral - Green

  Alkaline - Blue
• pH of exactly 7 = neutral
• pH less than 7 = acid

  • Strong acids have a pH close to 0.
  • Acids form hydrogen (H+) ions when they dissolve in water.
• pH more than 7 = alkali

  • Strong alkalis have a pH close to 14.
  • Alkalis form hydroxide (OH-) ions when they dissolve in water.
• Acid + hydroxide → salt + water
• Acid + carbonate → salt + water + carbon dioxide.
• Acid + oxide → salt + water.
• A neutralisation reaction happens when an acid reacts with an alkali
• A more reactive metal (one that forms positive ions more easily) can remove a less reactive metal from a compound. This is called a displacement reaction.
• A metal can only displace another metal from a compound if it is located above it in the reactivity series.
• A spectator ion is an ion that doesn't change during a chemical reaction
• When an ion touches an electrode, electrons can be transferred, producing elements.