Chemistry IGCSE

• Diffusion is when a substance moves from an area of high concentration to an area of lower concentration.
• The proton (atomic) number is the total number of protons in an atoms nucleus. (Smaller number)
• The nucleon (mass) number is the total number of protons and neutrons in an atoms nucleus. (Bigger number)
• Isotopes are atoms of the same element with the same number of protons but different number of neutrons.
• The molecular formula of a compound shows the number of different types of atoms in one molecule.
• The relative atomic mass of an element is the average mass of all the isotopes of an element compared to one twelfth of a 12C atom.
• The relative molecular mass of a compound is the relative atomic masses of all the atoms in the formula added together.
• One molecule of a substance contains 6.02 x 10^23 particles
• The number 6.02 x 10^23 is known as Avogadros constant.
• Number of moles = mass in g / Mr of substance
• Percentage yield= actual yield (g) / theoretical yield (g) x 100
• percentage purity = pure yield (g) / total impure yield (g) x 100
• percentage composition by mass = relative mass of each element in the compound / Mr of the compound x 100
• The empirical formula is the smallest whole number ratio of atoms in a compound
• Concentration (in mol/dm3) = number of moles / volume of solution (in dm3)
• One mole of any gas always occupies 24dm^3 at room temperature and pressure
• Volume (dm3) = Moles of gas x 24
• Electrolysis is the breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity.
• An exothermic reaction is one which gives out energy to the surroundings, usually in the form of thermal energy and usually shown by the rise in temperature of the surroundings.
• An endothermic reaction is one which takes in energy from the surroundings, usually in the form of thermal energy and usually shown by a fall in temperature of the surroundings
• The activation energy is the minimum amount of energy that colliding particles must have for bonds to break and the particles to react.
• Enthalpy change = energy required to break bonds - energy released by forming bonds
• The rate of reaction is how fast the reactants are changed into products.
• A catalyst speeds up reactions without being used up itself.
• Rate of reaction = amount of reactant used or amount of product formed / time
• Oxidation is the gain of oxygen
• Reduction is the loss of oxygen
• A redox reaction is a reaction where oxidation and reduction occur at the same time
• A loss of electrons is called oxidation
• A gain of electrons is called reduction
• An oxidation agent oxidises another substance during a redox reaction and becomes reduced itself
• A reducing agent reduced another substance during a redox reaction, and becomes oxidised itself
• An acid is a source of hydrogen ions (H+). They are proton donors.
• A base is a substance that can neutralise an acid. They are proton acceptors.
• A strong acid ionises almost completely in water, releasing a large proportion of H+ ions
• A weak acid does not fully ionise in water, only releasing a small proportion of H+ ions
• Acidic oxides will react with a base to form a salt and water.
• Basic oxides will react with an acid to form a salt and water.
• Amphoteric oxides will react with both acids and bases to form a salt and water.
• Water of crystallisation is water that exists as part of hydrated crystals