definations

• Activated complex


  An unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction
• Activation energy


  The minimum energy required by colliding molecules to form an activated complex
• Addition reaction


  Adding of hydrogen, a halogen or water across a carbon to carbon double bond (two molecules join to make a single molecule)
• Antioxidant


  Molecules that can act as free radical scavengers which prevent oxidation by acting as reducing agents
• Atom economy


  A measure of the proportion of reactants that have been converted into products
• Catalyst


  A catalyst provides an alternative reaction pathway with a lower activation energy
• Chromatography


  A technique used to separate the components present within a mixture by making use of differences in their polarity or molecular size
• Collision theory


  Explains how atoms can take part in a chemical reaction if they collide with sufficient energy (greater than the activation energy) and with the correct geometry
• Condensation reaction


  A reaction where two or more small molecules join to produce a larger molecule by eliminating of a small molecule usually (but not always!) water
• Covalent bond


  Bond formed between two atoms (usually non-metal) by sharing a pair of electrons. The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons
• Covalent network structure


  A very strong and stable structure formed by certain elements (C, Si and B) and certain compounds (SiO2 and SiC). All of the atoms are held together by strong covalent bonds and so have very high melting and boiling points
• Dehydration


  The removal of water from a single compound
• Dipole


  A pair of opposite charges created when two atoms in a bond have different electronegativities
• Electronegativity


  An atom's attraction for electrons within a covalent bond
• Electrolysis


  The process of breaking up a molten ionic compound using electricity
• Emulsifier


  Can be used to prevent non-polar and polar liquids separating into layers. An emulsion contains small droplets of one liquid dispersed in another liquid. Emulsifiers for use in food can be made by reacting edible oils with glycerol
• Essential amino acids


  Must be acquired from the diet. The body cannot make them
• Essential oils


  The concentrated extracts of the volatile, non-water-soluble aroma compounds from plants
• Exothermic reaction


  A reaction where heat energy is released and the temperature increases. Negative enthalpy change
• Endothermic reaction


  A reaction where heat energy is absorbed and the temperature decreases. Positive enthalpy change
• Enthalpy change


  The difference in energy between the reactants and the products. ΔH = EH products - EH reactants
• Enthalpy of combustion


  The enthalpy change when one mole of a substance burns completely in oxygen
• Enthalpy of solution


  The enthalpy change when one mole of a substance is dissolved in water to form a dilute solution
• Equilibrium


  Reversible reactions attain a state of dynamic equilibrium when the rates of forward and reverse reactions are equal. At equilibrium, the concentrations of reactants and products remain constant, but are rarely equal
• Fats/oils


  Made by esterification. Glycerol + 3 long chain carboxylic acids (fatty acids). Fats = unsaturated = higher m.pt.
• Free radical


  A highly reactive atoms or molecule with unpaired electrons
• Free radical scavenger


  A compound that terminates free radical reactions by reacting with free radicals (donating an electron to them) to produce a stable molecule
• Hard Water


  Water containing high levels of dissolved metal ions. When soap is used in hard water, scum, an insoluble precipitate, is formed
• Hess's Law


  Hess's law states that the enthalpy change for a chemical reaction is independent of the route taken
• Hydrogen bonds


  The strongest intermolecular force of attraction caused by highly polar bonds due to a large difference in electronegativity. Only present between molecules when in the molecule is O-H, or N-H or F-H bonds
• Hydrogenation


  Addition of a hydrogen molecule to an unsaturated compound e.g. converting alkenes into alkanes (and hardening of oils into fats)
• Hydrolysis


  The breaking down of a larger molecule, into smaller molecules, using water
• Hydration


  Addition of a water molecule to an unsaturated compound e.g. hydrating C2H4 to form C2H5OH
• Hydrophilic


  Describes molecules (parts of molecules) which repel fats and oils and are soluble in water e.g. the –OH group in alcohols
• Hydrophobic


  Describes molecules (parts of molecules) which repel water and are soluble in fats and oils e.g. a long hydrocarbon chain
• Hess's Law


  States that the enthalpy change of a chemical reaction is independent of the route taken
• Hydrogen bonding


  Hydrogen bonds are electrostatic forces of attraction between molecules that contain highly polar bonds due to the presence of Hydrogen bonded to Nitrogen, Oxygen or Fluorine in a molecule
• Ionic lattice


  Tightly packed group of ions formed from the attraction between positive and negative charges
• Ionisation energy


  The energy required to remove one mole of electrons from one mole of gaseous atoms
• Intramolecular bond


  Bonds within a molecules, such as covalent and polar covalent bonds