GCSE Chemistry Triple (Paper 2) AQA

• Closed system


  Reactants or products cannot enter or leave the system
• Reversible reaction


  Anhydrous copper sulfate (white) + water <=> Hydrated copper sulfate (blue)
• Collision theory


  Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
• Factors that affect the rate of a reaction


  • Concentration
  • Temperature
  • Pressure
  • Catalyst
  • Surface area
• Explaining the rate of reaction in terms of particles

  1. The higher the temperature, particles move faster

  2. The higher the concentration/pressure, more particles in a given volume

  3. The higher the surface area, more area for the reactants to collide

  
  

  ... the faster the rate of reaction due to a higher frequency of successful collisions.
• 
  

  • Loss of mass of the reactants (use balance)
  • Volume of gas produced (use a gas syringe or upturned measuring cylinder)
  • Time taken for the solution to become cloudy (place conical flask on cross and watch it disappear)
• Equipment needed to measure the Rate of Reaction:

  • Stop clock
  • Balance or measuring cylinder/gas syringe
• Activation Energy


  The minimum amount of energy that particles must have to react energy.
• What does it mean by equilibrium?

  The rate of the forward and reverse reaction is the same. The concentrations of reactants and products are constant. It is a closed system
• Equilibrium and temperature

  • Increase in temperature – reaction moves in the endothermic direction.
  • Decrease in temperature – reaction moves in the exothermic direction.
• Equilibrium and pressure

  • Increase in pressure – reaction moves to the side of the fewer moles.
  • Decrease in pressure – reaction moves to the side of the most moles.
• Equilibrium and concentration

  • Increase in concentration of a chemical– reaction moves to the opposite side to use up excess chemical.
  • Decrease in concentration of a chemical– moves to this side to create more of this chemical.
• Equilibrium and a catalyst

  • No effect on the position of equilibrium. A catalyst allows the reaction to reach equilibrium faster.
  • Increases the rate of the forward and the reverse reaction by the same amount.
• Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.
• Catalysts reduce energy costs.
• Catalysts are not included in the chemical equation for the reaction.
• A example of a catalyst is a biological catalyst such as enzymes.
• Rate of Reaction Graphs


  The steeper the curve, the faster the rate of reaction.

  Horizontal line on graph means reaction is finished (reactants used up).
• Rate = Change in mass/ change in time
• Calculating the rate at a specific time

  1. Draw a tangent at that point approximately 10 cm long.
  2. Draw a triangle
  3. Calculate change in y
  4. Calculate change in x
  5. Gradient = change in y/ change in x
• Method for Rate of Reaction by collecting a gas [Required Practical]

  1. Set up a conical flask and a gas syringe.
  2. Add 5 cm magnesium strip and 30 cm3 of a highly concentrated acid into the conical flask.
  3. Collect gas for 1 minute.
  4. Repeat steps 1-3 with different concentrations of acid.
• Rate of Reaction by collecting a gas- Independent Variable


  Concentration of acid
• Rate of Reaction by collecting a gas- Dependent Variable


  Volume of gas collected in 1 minute
• Rate of reaction by collecting gas - Dependent Variable


  Volume and type of acid, length of magnesium strip, time period of gas collection
• Method for measuring rate of reaction by the formation of a precipitate [Required Practical]

  1. Place conical flask on a black cross
  2. Add sodium thiosulfate and hydrochloric acid to the flask.
  3. Time how long it take for the cross to disappear.
  4. Repeat steps 1-3 with different concentrations of sodium thiosulfate
• Measuring rate of reaction by the formation of a precipitate- Independent Variable


  Concentration of acid
• Measuring rate of reaction by the formation of a precipitate- Dependent Variable


  Time taken for cross to disappear
• Measuring rate of reaction by the formation of a precipitate- Controlled Variable


  Volume and type of acid
• Why is there mass loss during the Rate of Reaction [Required Practical]?

  Sulfur dioxide gas is made, which escapes into the air.
• The solution in the conical flask turns cloudy because solid sulfur is made.
• The rate of reaction is greater when the surface area is increased.