MOD 5: EQUILIBRIUM AND ACID REACTIONS

• Removing water from hydrated cobalt (II) sulfate

  Heating
• Collecting and condensing water vapour


  In a second test tube sitting in a beaker of water
• Rehydrating anhydrous cobalt (II) sulfate


  Resulting in the return of the blue colour
• The solution contains spectator ions K+ and NO3(-)
• In the slightly acidic solutions

  Fe+3 is light yellow, SCN- is colourless and FeSCN+2 is red
• Burning magnesium goes to completion (until magnesium strips are fully converted into magnesium oxide)
• It is an irreversible reaction because magnesium oxide is very stable at standard conditions
• The activation energy of the reverse reaction (endothermic) is also much larger
• The product of the burn is bits of rust, or iron oxide, just as the product of burning wood is black ash (or carbon)
• Because of the high amount of energy required to break the Fe-O bond and difficulty to reverse such reaction under normal circumstances, the burning of steel wool is irreversible
• Open system


  Substances that can be added or lost
• Closed system


  Chemicals in the reaction are all contained within a certain space
• For a reaction to be reversible, it must occur in a closed system as reactants and products cannot be lost
• Isolated system


  No exchange of energy or matter
• Static equilibrium


  Forward and reverse reaction are not occurring at all. It is the equilibrium of a system at rest
• Most irreversible reactions once completed reach a state of static equilibrium
• Most irreversible reactions involve combustion (burning)
• In static equilibrium, the system does not change as there is no reaction occurring (no change at all)
• Dynamic equilibrium


  Both the forward and reverse reactions are occurring at the same rate. It can only be achieved in a closed system
• At dynamic equilibrium, the macroscopic properties of the reaction vessel (temperature, concentration and pressure) will remain constant
• Physical change


  Products do not include any new substances → physical properties of the reactant change (e.g. change of state)
• Chemical change


  Reactants produce new substances with different physical and chemical properties. Atoms rearrange to form products that are different from the reactants (e.g. CO + NO2 ⇌ CO2 + NO)
• Non equilibrium systems


  A reaction goes fully to completion —> occurs when the forward reaction is favoured
• The free energy of a system at equilibrium is 0. → ΔG = 0
• If a system has a large ΔG, it will not react without some energy input so a non-equilibrium system will be established
• Non-equilibrium systems include combustion and photosynthesis which occur in open systems
• Dynamic equilibrium occurs in reactions that are spontaneous/reversible
• If a reaction occurs but the reverse reaction is not possible, a non equilibrium system will be established
• Combustion


  Occurs in an open system, and thus is irreversible. Exothermic → drives the reaction to completion and the activation energy of the reverse reaction is very high, therefore irreversible. Combustion is spontaneous
• Photosynthesis


  ΔS < 0, Endothermic (ΔH > 0) and involves a decrease in entropy (ΔS < 0) which would mean that ΔG is always > 0. Photosynthesis is non-spontaneous → irreversible
• Spontaneity


  Reaction that occurs is spontaneous → exergonic (release energy). Reaction that occurs is non-spontaneous → endergonic (absorbs energy). If ΔG is negative, the reaction favours the forward reaction. If ΔG is positive, the reaction favours the reverse reaction
• Collision theory


  Reacting particles need to have sufficient energy to break current bonds → must collide with enough force to overcome activation energy. Collide with correct orientation
• Reaction rate


  Speed at which a reaction occurs. Reaction rate is directly proportional to the collision rate of reacting molecules. Fast rate: how quickly the reactant particles interact and form new substances. Slow rate: analysing reaction rates and determining the position, the reactants, the intermediates, or the products of the reaction
• Factors that affect rate of reaction

  • Concentration of reactants
  • Temperature of surroundings
  • Pressure (if gases are involved)
  • Catalyst
• Le Chateliers principle


  If an equilibrium system is disturbed (temperature, concentration, volume/pressure), the system will adjust itself to minimise/balance/counteract the change
• The relative concentrations of reactants and products, will determine if the forward or reverse reaction is favoured
• Equilibrium position is to the left = higher concentration of reactants. Equilibrium position is to the right = higher concentration of products
• The equilibrium position is based on changes to the forward or reverse reaction rate
• If the concentration of CO is increased, the frequency of successful collisions of that reactant would increase as well, allowing for an increase in the forward reaction, and thus the generation of the product
• Complex ion


  An ion that has a metal ion in its centre and a number of other molecules or ions surrounding it