Chemistry Alevel Aqa

• What’s stereoisomerism?

  molecules with the same structural formula but a different arrangement of atoms in space.
• For E/Z isomerism to happen what has to be the case?

  Both carbons on the double bond must be bonded to 2 different atoms or groups of atoms.
• Z isomer vs E isomer

  Z isomers have the larger mr on the same side, whereas E isomers have it on opposite sides. (Zame)
• Why are alkenes reactive?

  There’s a high electron density in the double carbon bond. The double carbon bond is much stronger than the single carbon bond.
• Which carbocation intermediate the most stable?

  The tertiary carbocation is the most stable followed by the secondary carbocation and finally the primary carbocation.
• Why is the secondary carbocation more stable than the primary carbocation?

  The greater number of methyl groups present on the secondary carbocation are more electron releasing, hence, they have a greater positive inductive effect.
• Addition reaction=

  Increases the number of substituents attached as a double bond’s converted to a single band.
• Elimination reaction=

  A reaction in which an atom or group of atoms is removed from a reactant.
• What’s an acid?

  A proton donor
• What’s a base?

  A proton acceptor
• addition polymerisation summary

  addition polymers tend to have induced dipole dipole forces between the polymer chains and strong carbon to carbon bonds within the polymer chains. The bonds in the polymer chain and not polar this makes the bonds not very susceptible to attack from nucleophiles. This makes the polymers unreactive and non-biodegradable. They are used as insulators, packaging and making containers. The polymers have relatively high melting and boiling points.
• Define enthalpy change

  An enthalpy change is the heat energy change at a constant pressure
• Define bond enthalpy

  Bond enthalpy is the energy required to break one mole of a given covalent bond in the gaseous state into gaseous atoms
• Define the standard enthalpy formation

  This is the enthalpy change that occurs when one mole of a compound is formed from its constituent elements with all reactants and products in their standard states under standard conditions
• When an element is in its standard state, what is its value in kilojoules per mole?

  Zero
• Define standard enthalpy of combustion

  The enthalpy change that occurs when one mole of a compound is burned completely in oxygen with all reactants and products in their standard states under under standard conditions
• State Hess’s law

  Hess’s law states that the enthalpy change at a constant pressure in a reaction is independent of the route taken
• Define specific heat capacity

  The amount of energy needed to make 1 g of a substance 1 degree Celsius hotter
• q=

  mcΔT
• ΔH=

  q/n
• We can calculate the standard enthalpy of combustion of methanol using mean bond values and by using calorimetry. The two values for standard enthalpy of combustion will not be the same this is due to….

  .Heat lost to the surroundings

  .Incomplete combustion of the fuel .Mean bond enthalpies are calculated over range of molecules, so not specific to the reaction that’s being studied
• What’s oxidation?

  loss of electrons
• Whats reduction

  Gain of electrons
• What is a strong acid?

  One that fully dissociates into its ions in aqueous solution
• What does a decrease in oxidation states mean?

  It has been reduced and is the oxidising agent
• What is a disproportionation reaction?

  A reaction in which the same species is simultaneously oxidized and reduced.
• What’s activation energy

  The minimum amount of energy needed for a reaction to occur
• What’s necessary for a successful collision to occur?

  The collisions must have energy equal to or greater than the activation energy
• Rate of reaction definition

  The change in concentration of a reactant/product per unit time
• how does an increase in concentration or increase in pressure affect the reaction rate?

  increase the reaction rate because the number of reactant molecules per unit volume are increased. This increases the number of successful collisions per unit time.
• How does a decrease in particle size affect the reaction rate?

  As you decrease the particle size you increase the surface area, this reveals more surface of the reagent to react with. This increases the number of successful collisions per unit time.
• How does an increase in temperature affect the reaction rate?

  It increases the reaction rates as it increases the kinetic energy of the molecules. At a higher temperature, many more molecules have the kinetic energy greater than or equal to the activation energy. This results in there being more successful collisions per unit time.
• What’s a catalyst 


  A substance that increases the rates of a chemical reaction and can be recovered chemically unchanged at the end
• How does a catalyst work?

  It provides an alternate reaction pathway that has a lower activation energy
• As temp increases on a maxwell boltzmann distribution curve, what happens to the curve

  It lowers and moves to the right
• When adding a catalyst to a Maxwell Boltzman distribution curve, what happens?

  The activation energy shifts to the left meaning there are more products with energy greater than the activation energy
• Why are halogenoalkanes much more reactive than alkanes?

  There’s is a polar bond present. The halogens more electronegative than the carbon.
• Uses of halogenoalkane

  Refrigerants, aerosol, solvents and pharmaceuticals
• Structural isomers

  Molecules with the same molecular formula but different structural formula
• Chain isomers

  molecules that have the same molecular formula, but their structures have their carbon chain arranged differently