unit 2 keywords

• Bond enthalpy

  The amount of energy required to break one mole of the stated bond in the gas phase
• Enthalpy change (ΔH)

  The heat energy change measured under a constant pressure
• Enthalpy change of reaction

  The enthalpy change when quantities of substances in standard states react completely
• Enthalpy of combustion

  The enthalpy which occurs when one mole of a compound is burned completely in oxygen under standard conditions, with everything in its standard state.
• Hess's law

  The enthalpy change of a reaction is independent of the route taken
• Mean bond enthalpy

  The enthalpy change when one mole of a specified covalent bond is broken averaged out across the range of compounds
• Standard enthalpy of formation (ΔfHθ)

  The enthalpy which occurs when one mole of a compound is formed from its elements under standard conditions, with everything in its standard state.
• Activation energy


  The minimum amount of energy for particles to collide with for a successful reaction to take place
• Catalyst


  A substance that increases the rate of a reaction without being changed in chemical composition or amount. They work by providing an alternative reaction pathway with a lower activation energy
• Collision theory


  Reactions can only occur when collisions take place between particles that have sufficient energy
• Colorimetry


  This method is used to calculate the concentration of a specific coloured compound in a solution by measuring the extent to which it absorbs certain wavelengths of light. This is measured with a colorimeter
• As the concentration of reactants increases


  The reacting particles get closer together meaning they will collide more often. As a result, there will be a higher rate of successful collisions and a faster rate of reaction
• As the pressure of gaseous reactants increases


  The reacting particles get closer together meaning they will collide more often. As a result, there will be a higher rate of successful collisions and a faster rate of reaction
• Increasing the temperature


  The particles will have more kinetic energy and so will move faster. If the molecules are moving faster they will collide more often and, since they've gained kinetic energy, a larger proportion of the particles will have at least the activation energy. For both these reasons the rate of reaction increases
• Energy profile


  A graph used to show the relative energy of reaction species (including reactants and products) as a reaction proceeds
• Maxwell-Boltzmann distribution


  Shows the distribution of the molecular energies in a gas at a constant temperature. The area under the curve indicates the total number of particles present
• Rate of reaction


  The measure of the amount of product formed or reactant used over time. The units of rate of reaction may be given as g/s, cm3/s or mol/s
• Biofuels


  Fuels made from once-living organic matter. These fuels are renewable and sustainable and are an alternative to fossil fuels
• Synthesis


  The process of combining different elements and compounds to build new molecules
• Sustainability


  The process of using resources at a rate that allows their supply to be maintained
• Green chemistry


  Chemistry that aims to be sustainable in terms of energy and resources and restricts pollution
• Alcohol


  An organic compound containing the functional group -OH
• Alkane


  A homologous series of saturated hydrocarbons with the general formula CnH2n+2
• Alkene


  An hydrocarbon containing at least one C=C double bond with the general formula CnH2n
• Boiling temperature


  The temperature at which a substance changes from a liquid state to a gaseous state
• Carboxylic acid


  An organic compound containing the -COOH functional group
• Displayed formula


  The relative positions of atoms and the bonds between them
• Electrophile


  A species that can accept electrons in a reaction, to form a chemical bond. Electrophiles are attracted to areas with a lot of electrons/high negative charge
• Functional group


  An atom/group of atoms responsible for the characteristic reactions of a compound
• Halogenoalkane


  A saturated molecule where one or more of the hydrogen atoms in an alkane have been substituted for a halogen
• Heterolytic (bond breaking)


  The type of bond breaking in which both the electrons from the bond move together to one of the bonding atoms
• Homolytic (bond breaking)


  The type of bond breaking in which the electrons from the bond move separately, one goes to each of the atoms of the bonding pair
• Melting temperature


  The melting point of a substance is the temperature at which it changes from solid state to liquid state
• Nucleophile


  An atom or molecule that donates an electron pair to form a covalent bond. Attracted to electron-deficient areas
• Organic compound


  A carbon-containing compound
• Radical


  A species with an unpaired electron. Represented in mechanisms by a single dot
• Skeletal formula


  The simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving the carbon skeleton and the functional groups
• Solubility


  The ability of a given substance to dissolve in a solvent
• Structural formula


  Shows the arrangement of atoms in a molecule
• Structural isomer


  Structural isomers are compounds that have the same molecular formula but a different structural formula. Structural isomers include chain isomers, functional group isomers and position isomers