Chemical Reactions

• Physical and chemical changes


  Identify and describe the differences between them
• Rate of reaction


  1. Describe the effect on the rate of reaction of:

  2. Changing the concentration of solutions

  3. Changing the pressure of gases

  4. Changing the surface area of solids

  5. Changing the temperature

  6. Adding or removing a catalyst, including enzymes
• A catalyst increases the rate of a reaction and is unchanged at the end of a reaction
• Practical methods for investigating the rate of a reaction

  1. Change in mass of a reactant or a product

  2. Formation of a gas
• Interpret data, including graphs, from rate of reaction experiments
• Collision theory


  • Number of particles per unit volume
  • Frequency of collisions between particles
  • Kinetic energy of particles
  • Activation energy, Ea
• Describe and explain the effect on the rate of reaction of:

  1. Changing the concentration of solutions

  2. Changing the pressure of gases

  3. Changing the surface area of solids

  4. Changing the temperature

  5. Adding or removing a catalyst, including enzymes
• A catalyst decreases the activation energy, Ea, of a reaction
• Evaluate practical methods for investigating the rate of a reaction

  1. Change in mass of a reactant or a product

  2. Formation of a gas
• Rate of reaction


  Change in concentration of reactants divided by change in time
• Reactions occur as the result of two particles colliding with enough energy (activation energy)
• Factors that increase the rate of reaction

  • Increase the number of collisions
  • Increase the energy of those collisions
• Factors affecting rate of reaction

  • Concentration (pressure in gases)
  • Temperature
  • Particle size
  • Catalyst
• Reaction rates increase if you increase the number of collisions, the energy of those collisions, temperature, concentration and surface area
• Using a catalyst decreases the energy needed for a reaction
• Design an investigation


  1. Sodium thiosulphate + hydrochloric acid

  2. Calcium carbonate + hydrochloric acid

  3. Magnesium + hydrochloric acid

  
• Some chemical reactions are reversible
• Reversible reaction at equilibrium

  • Rate of forward reaction is equal to rate of reverse reaction
  • Concentrations of reactants and products are no longer changing
• Predict and explain how the position of equilibrium is affected by:

  1. Changing temperature

  2. Changing pressure

  3. Changing concentration

  4. Using a catalyst
• At dynamic equilibrium, the concentration of reactants and products are constant but not equal
• The rate of the forward reaction is equal to the rate of the back reaction at equilibrium
• Dynamic equilibrium


  The reaction hasn't stopped, it is still going, but the rate of the forward and back reactions are equal, so there is no overall change
• Le Chatelier's Principle: A system at equilibrium responds to disturbances in such a way as to minimise that disturbance
• How equilibrium shifts in response to changes in:

  1. Concentration

  2. Pressure

  3. Temperature
• Adding a catalyst does not affect the equilibrium position
• The Haber process produces ammonia from nitrogen and hydrogen gases
• The Contact process converts sulfur dioxide to sulfur trioxide
• Typical conditions in the Haber process

  • 450°C
  • 20000kPa/200atm
  • Iron catalyst
• Typical conditions in the Contact process

  • 450°C
  • 200kPa/2atm
  • Vanadium(V) oxide catalyst
• Explain why the typical conditions are used in the Haber process and Contact process

  1. In terms of rate of reaction and position of equilibrium

  2. Including safety considerations and economics