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AS Definitions – Paper 2
1.1 Amount of substance: Relative molecular mass, Mr: Covalent molecules (non metal & non metal): The weighted mean mass of a molecule compared with 1/12th^ of the mass of carbon - 12 Relative formula mass, Mr: Ionic compounds (metal & non metal): The weighted mean mass of a formula unit compared with 1/ th of the mass of carbon - 12 The mole: Avogadro’s constant, NA: 6.02 X 10 23 No^ **particles = Moles x NA
- Moles and masses Number of moles = Mass of substance Mr n = m Mr** TIP: mass must be in g so make sure you can convert to this. k means 1000’s of, ie 1000 of grams: X 1000 / 1000 1kg à 1000g 1000g à 1kg X 1 x 10^6 / 1 x 10^6 1tonne à 1000000g 1000000g à 1tonne
2) Moles and Solutions, (aq) – mol dm
**- 3 Number of moles = Concentration x Volume (mol dm
- 3 ) (dm 3 ) n = C x V (dm**^3 ) TIP: Volume must be in dm^3 so make sure you can convert to this: 1dm 3 = 1000cm 3 = 1litre X 1000 / 1000 1dm^3 à 1000cm^3 1000cm^3 à 1dm^3 3) Moles and gases, (g) – M^3 The Ideal gas equation 2 assumptions: Ø The volume of the molecules is negligible Ø The molecules have no intermolecular forces of attraction TIP: Volume must be in m^3 so make sure you can convert to this: 1000000cm^3 = 1000dm^3 = 1m^3 x 1000 x 1000 x 1000000 1m^3 à 1000dm^3 1000dm^3 à 1000000cm^3 1m^3 à 1000000cm^3 / 1000 / 1000 / 1000000 1000000cm (^3) à 1000dm 3 1000dm (^3) à 1m 3 1000000cm (^3) à 1m 3 TIP: Temperature must be in kelvin, K so make sure you can convert to this: +273 +273 + 0 oC à 273K 100 oC à 373K 25 oC à 298K
- 273 - 273 - 273 273K à 0 oC 373K à 100 oC 298K à 25 oC
1.4 Energetics Enthalpy change Is the change in heat energy at constant pressure Exothermic reaction When heat energy is transferred from the system to the surroundings, negative values Endothermic reaction When heat energy is transferred from the surroundings to the system, positive values Activation energy Is the minimum energy required to start a reaction by the breaking of bonds Bond Enthalpy Is the energy required to break one mole of a given covalent bond in the molecule in the gaseous state Mean bond Enthalpy Is the average value for the bond enthalpy over the range of compounds it is found in Standard enthalpy change of formation, ΔfH^ θ The enthalpy change that occurs when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions. H2(g) + ½O2(g) à H 2 O(l) Standard enthalpy of combustion – ΔcH^ θ The enthalpy change that occurs when 1 mole of a compound reacts completely with oxygen under standard conditions where all reactants and products are in their standard states. CH4(g) + 2O2(g) à CO2(g) + 2H 2 O(l) Standard enthalpy change of reaction,^ ΔrH^ θ The enthalpy change when a reaction occurs in the molar quantities shown in the equation under standard conditions where all reactants and products are in their standard states. Fe 2 O3(s) + 2Al(s) à 2Fe(s) + Al 2 O3(s) Hess’s law The total enthalpy change for a reaction is independent of the route taken.
1.5 Kinetics Activation energy The minimum amount of energy that particles require to react when they collide by the breaking of bonds Rate The rate of a reaction is the change in concentration of a reactant or product in a given time 1.6 Equilibria Le Chatelier’s Principle When a reaction at equilibrium is subject to a change in concentration, pressure or temperature, the position of the equilibrium will move to counteract the change. 3.1 Introduction to organic chemistry Hydrocarbon: A compound that contains only hydrogen and carbon Saturated: A compound that contains single carbon – carbon bonds only Unsaturated: A compound that contains one or more carbon – carbon double bonds Molecular formula: The actual number of atoms of each element in a compound Empirical formula: Simplest whole number ratio of atoms of each element in a compound Displayed formula: Shows all the atoms and bonds in a molecule Structural formula: Shows how the atoms in a molecule are arranged
Elimination Where a molecule loses atoms or groups of atoms Hydrolysis Splitting a molecule apart by using water molecules 3.2 Alkanes 3.3 Halogenoalkanes 3.4 Alkenes Geometric Isomerism (E/Z isomerism) These have the same molecular formula but different spatial arrangement due to the restricted rotation around the carbon – carbon double bond 3.5 Alcohols Carbon neutral The amount of CO 2 taken in through photosynthesis and fermentation is the same as the amount of CO 2 released from combustion
