Terms & Definitions in Advanced Subsidiary Chemistry 0.0 / 5HideShow resource informationChemistryTerms & DefinitionsASCIECreated by: K.T.1998Created on: 07-10-16 11:25 Relative Atomic Mass The weighted average mass of naturally occurring atoms of an element on a scale where an atom of carbon-12 has a mass of exactly twelve units. 1 of 21 Relative Isotopic Mass The mass of a particular isotope of an element on a scale where an atom of carbon-12 has a mass of exactly twelve units. 2 of 21 Formula Mass The mass of one formula unit of a compound measured on a scale on which an atom of the carbon-12 isotope has a mass of exactly twelve units. 3 of 21 Empirical Formula The formula that tells us the simplest ratio of the different atoms present in a molecule. 4 of 21 Molecular Formula The formula that tells us the actual numbers of each type of atom in a molecule. 5 of 21 Mole The amount of a substance that has the same number of specific particles as there are atoms in exactly twelve grams of the carbon-12 isotope. 6 of 21 Bond Energy The energy needed to break one mole of a particular bond in one mole of gaseous molecules. 7 of 21 Bond Length Average distance between the nuclei of two bonded atoms in a molecule. 8 of 21 Enthalpy Change of Reaction The standard enthalpy change when the amounts of reactants shown in the equation react to give products under standard conditions. 9 of 21 Enthalpy Change of Formation The standard enthalpy change when one mole of a compound is formed from its elements under standard conditions. 10 of 21 Enthalpy Change of Combustion The standard enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions. 11 of 21 Enthalpy Change of Hydration of an Anhydrous Salt The standard enthalpy change when one mole of a hydrated salt is formed from one mole of the anhydrous salt under standard conditions. 12 of 21 Enthalpy Change of Solution The standard enthalpy change when one mole of solute is dissolved in a solvent to form an infinitely dilute solution under standard conditions. 13 of 21 Enthalpy Change of Neutralisation The standard enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard conditions. 14 of 21 Enthalpy Change of Atomisation The standard enthalpy change when one mole of gaseous atoms is formed from its element in their standard state under standard conditions. 15 of 21 Reversible Reaction A reaction in which products can be changed back to reactants by reversing the conditions. 16 of 21 Dynamic Equilibrium In an equilibrium mixture, molecules of reactants are being converted to products at the same rate as products are being converted to reactants. 17 of 21 Le Chatelier's Principle When any of the conditions affecting the position of equilibrium are changed, the position of that equilibrium shifts to minimise the change. 18 of 21 Rate of Reaction The measure of a rate at which reactants are used up or the rate at which products are formed. 19 of 21 Activation Energy The minimum energy required in order for a reaction to take place. 20 of 21 Catalyst Substance that increases the rate of a reaction but remains chemically unchanged itself at the end of a reaction. 21 of 21
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