Higher Chemistry

• Activated Complex


  An unstable arrangement of atoms formed at maximum potential energy

  
• Activation Energy


  The minimum energy required for particles to successfully react.(Ea)

  
• Addition Reaction


  A reaction which two or more molecules combine to produce a larger molecule and nothing else.

  
• Alcohols


  Carbon compounds which contain the hydroxyl (-OH) functional group.

  
• Aldehydes


  Carbon compounds which contain the functional (-CHO) group -on the end carbon-. They are formed by oxidation of primary alcohols and can be further oxidised to form carboxylic acids.

  
• Alkanes


  A homologous series of saturated (single bonded) carbons with the general formula CnH2n+2.

  
• Alkenes


  A homologous series of unsaturated (contains double bonds) hydrocarbons with the general formula CnH2n.

  
• Amide Link


  The amide link is CONH and is formed in a condensation reaction which joins together amino acids. It can also be known as a peptide link.

  
• Amine


  A compound with the amine functional group (-NH(2))

  
• Amino Acids


  Acids with the general formula-C2NCHRCOOH- which link by a condensation reaction to form proteins.

  
• Antioxidants


  Compounds which slow oxidation reactions. Commonly added to food to prevent oxidation(the food going rancid).
• Atom Economy


  A measure of the amount of reactants that have been made into products. Formula- Atom economy= Mass of desired product/mass of reactants * 100. The answer is given as a percentage. The higher the atom economy the better as it means a higher yield and therefore less waste.

  
• Average Rate


  Rate=Change in x/change in y

  X will normally be something like mass or concentration and Y will be some unit of some. The unit of rate always contains some unit of time ^-1.
• Carbonyl Group


  The C=O functional group present in ketones and aldehydes.

  
• Carboxyl Group


  The functional group present in carboxylic acids-COOH.

  
• Carboxylic Acids


  Carbon compounds which contain the carboxyl functional group (-COOH) which can be formed from the oxidation of aldehydes.

  
• Catalyst


  A substance that speeds up a reaction but does not take part in it preventing it from being used up. A catalyst lowers the activation energy of a reaction, providing a different pathway for the particles. IT DOES NOT GIVE THE PARTICLES ENERGY.

  
• Chromatography


  Chromatography is a technique for separating substances by size or polarity. This technique uses a mobile phase of gas or liquid passing over a stationary phase of a solid or liquid-impregnated solid. It can be use to identify the substances in a solution.

  
• Closed System


  In a closed system the reaction vessel is designed so that reactants and products can not escape. Reversible reactions will only reach dynamic equilibrium if the reaction is designed as a closed system.
• Concentration


  The amount of solute dissolved in a given volume of solution. A common unit of concentration is moles per litre(mol l^-1)
• Condensation Reaction


  A reaction in which two or more molecules join together by the elimination of a small molecule, E.G- water. An example of a condensation reaction is the making of esters, where an alcohol and a carboxylic acid join together by the elimination of water to form and ester.

  
• Covalent bonding


  The bonding between two atoms through the sharing of electrons which occurs between two non metals.

  
• Covalent Molecular


  A type of covalent bonding which occurs between small non metal molecules. Covalent molecular molecules have low melting/boiling points as they are only held together by London Dispersion Forces and can not conduct electricity as they do not have free moving electrons or ions.

  
• Covalent Network


  A type of Covalent bonding where all atoms are held together by strong covalent bonds. This only occurs in Boron, Silicon and Carbon (as carbon and also in the form Graphite(Diamond)). Covalent Networks have high melting/boiling points as it takes a lot of energy to break the strong covalent bond and in general do not conduct electricity apart from Graphite which can conduct as due to its hexagonal structure it has a free moving electron which is able to moves between its layers.

  
• Covalent Radius


  A measure of an atomic size, taken as half the distance between two covalently bonded atoms of an element. It decreases across a period as the nuclear charge increases holding the electrons tighter. It DECREASES down the group as the number of electron shells increases shielding the outer electrons from the nuclear charge and preventing them from being held as tight.

  
• Dehydration


  The removal of water from a single compound. An example of this is the dehydration of Ethanol to form Ethene.

  
• Delocalised Electrons


  Electrons which are not confined to a single orbital between pairs of atoms and are free to move in any way from the atom they came from. Delocalised electrons allow metals to conduct electricity.

  
• Denaturing


  The changing of shape of a protein caused by increase in temperature or reduction in PH. If a protein such as an enzyme( a biological catalyst) is denatured it will not longer be functional.
• Detergent


  A soap like molecule which can dissolve fats and oils. Detergents are better then soap as they do not cause the formation of scum. Detergents do not contain a carboxylate head(COO^-) unlike soaps.
• Displacement


  A redox reaction where a metal high in the electrochemical series reacts with a metal compound which is lower in the electrochemical series to become a metal compound( High metal) and a metal (Low compound).

  
• Distillation


  A method used to separate liquid mixtures based on their boiling points. A liquid is boiled and the vapour is then condensed to collect a pure sample of one of the substances present in the liquid mixture. Distillation can be used to increase the concentration of ethanol in a substance which has undergone fermentation.

  
• Electronegativity


  The attraction an atom has for its bonding electrons. It is measured on the Pauling scale which has no units. As you go along the period the electronegativity increases as the nuclear charge increases causing the atom to be more attracted to it's outer electrons. Down the group it decreases as the amount of shells increases and therefore the outer electrons are more shielded from the nuclear charge of the atom. The differences in electronegativity between two elements also indicates the polarity. If two atoms have a difference in electronegativity of less the 0.3 then the molecule is likely to be non polar where as between 0.3 and 2 it is likely to be Polar. If the electronegativity is bigger then 2 it will be ionic.

  
• Emulsifier


  A compound which allows oil and water to mix. Often present in salad dressings.
• Emulsion


  A mixture of liquids where small droplets of one liquid are dispersed in another liquid. Emulsions of oil and water are commonly found in food.
• Endothermic Reaction


  A reaction that takes in heat energy from the surroundings. An exothermic reaction has a positive enthalpy change and on a potential energy diagram the products energy will be higher then the reactants energy.

  
• Enthalpy Change


  The difference in heat energy between reactants and products in a reaction.

  
• Enthalpy of Combustion


  The enthalpy change when one mole of a substance is completely burned in oxygen.
• Enzyme


  A globular protein which is able to catalyse a specific reaction.

  
• Equilibrium


  State attained in a reversible reaction when the forward and backward reaction rates and equal and their concentrations are constant.
• Essential Amino Acids


  Amino acids which can not be produced by the body and must be obtained through diet.