Paper 2 Chemical Change Section

Energy and Chemical Change
Energy changes in reactions to bond energy changes

• Explain the concept enthalpy and its relationship to heat of reaction
• Define exothermic and endothermic reactions
• Identify that bond breaking requires energy (endothermic) and that bond formation releases ernergy (exothermic)

Exothermic and endothermic reactions

• State that ΔH > 0 for endothermic reactions, including graph
• State that ΔH < 0 for exothermic reactions, including graph

Activation energy

• Define activation energy
• Explain a reaction process in terms of energy change and relate this change to bond breaking anf formation, and to the "activated complex"

Rate and Extent of Reaction
Rates of reaction and factors affecting rate
· nature of reacting substances
· concentration
· pressure (gases)
· temperature
· catalyst
· state of division

• Explain what is meant by reaction rate
• List the factors which affect the rate of chemical reactions
  · concentration (solutions)
  · pressure (gases)
  · temperature
  · catalyst
  · surface area (solids)
• Explain in terms of the collision theory how the various factors affect the rate of chemical reactions

Measuring Rates of Reactions

• Suggest suitable experimental techniques for measuring the rate of a given reaction including the measuring of:
  · gas volumes
  · turbidy (precipitate formation)
  · change of colour
  · and the change of mass of the reaction vessel
  

Mechanism of Reaction and of Catalysis

• Define activation energy
  the minimum energy required for a reaction to take place.
  Colliding molecules must have, apart from the correct orientation, a kinetic energy equal to or bigger than the activation energy of a reaction before the reaction can take place
• Use a graph showing the distribution of molecular energies (number of particles against their kinetic energy) to explain why only some molecules have enough energy to react and hence how adding a catalyst and heating the reactants affects the rate
• Explain (in somple terms) how some catalysts function by reacting with the reactants in such a way that the reaction follows an alternative path of lower activation energy

Chemical Equilibrium and Factors affecting equilibrium

• Explain what is meant by:
  · Open and Closed systems
  · a Reversible reaction
  · a Dynamic equilibrium
• List the factors which influence the position on an equilibrium

Equilibrium Constant

• List the factors which influence the value of the equilibrium constant
• Write down an expression for the equilibrium constant having been given the equation for the reaction
• Perform calculations based on K_c values
• Explain the significance of high and low values of the equilibrium constant

Application of Equilibrium Principles

• State Le Chateliers Principle.
  · Use Le Chateliers Principle to identify and explain the effects of changes of pressure, temperature, and concentration on the concentrations and amounts of each substance in an equilibrium mixture.
  · Explain the use of a catalyst and its influence on an equilibrium mixture
• Interpret graphs of equilibrium
• Apply the rate and equilibrium principles to important industrial applications

Electrochemical Cells
Electrolytic and Galvanic cells

• Define the galvanic cell in terms of:
  · Self sustaining electrode reactions
  · Conversion of chemical energy to elelctrical energy
• Define the electrolytic cell in terms of:
  · Electrode reactions that are sustained by a supply of electrical energy
  · Conversion of electrical energy into chemical supply
• Define oxidation and reduction in terms of electron transfer / oxidation numbers
• Define anode and cathode in terms of oxidation and reduction
• Define oxidising and reducing agents in terms of electron transfer / oxidation numbers

Relation of current and potential to rate and equilibrium

• Give and explain the relationship between the current in an electrochemical cell and the rate of the reaction
• State that the pd of the cell (V_cell) is related to the extent to which the spontaneous cell reaction has reached equilibrium
• State and use the qualitative relationship between V_cell and the concentration of product ions and reactant ions for the spontaneous reactions
  · viz V_cell decreases as the concentration of product ions increase and the concentration of reactant ions decreases, until equilibrium is reached
  · at which the V_cell = 0 (the cell is "flat")
  · (qualitative only-exclude Nernst equation)

Understanding of the processes and redox reactions taking place in cells

• Describe:
  · movement of ions through the solutions
  · electron flow in the external circuit of the cell
  · the half reactions at the electrodes
  · function of the salt bridge in galvanic cell
• Use cell notation or diagrams to represent a galvanic cell

Standard Electrode Potentials

• Give the standard conditions under which standard electrode potentials are determined
• Describe"
  · the standard hydrogen electrode
  · explain its role as the reference electrode
• Explain how the standard electrode potentials can be determined using the reference electrode and state the conversion regarding positive and negative values
• Use the Table of Standard Reducation Potentials to calculate the emf of a standard galvanic cell.
• Use a positive value of the standard emf as an indication that the reaction is spontaneous under standard conditions

Writing of equations representing oxidation and reduction half reactions and redox reactions

• Predict the half-cell in which oxidation will take place when connected to another half-cell
• Predict the half-cell in which reduction will take place when connected to another half-cell
• Write equations for reactions taking place at the anode and cathode
• Deduce the overall cell cell reaction by combining two half-reactions
• Describe, using half equations and the equation for the overall cell reaction, the layout of the particulr cell using a schematic diagram and potential risks to the environment of the following processes used industrially:
  · the production of chlorine (the chloroalkali industry)
  · the recovery of aluminium metal from bauxite (South Africa uses bauxite from Australia