C8 - Rates and equilibrium

• Rate of reaction

  how quickly the reactants turn into the products
• mean rate of reaction = quantity of reactant used / time taken
• mean rate of reaction = quantity of product formed / time
• rate = volume of gas produced / time
• Measuring volume of gas


  • the reaction mixture is connected to a gas syringe or upside down measuring cylinder
  • as the reaction proceeds, the gas is collected
• Unit for rate


  cm^3/s
• Rate from graphs


  • steep gradient = high rate of reaction
  • the reaction took place quickly
  • shallow gradient = slow rate of reaction
  • the reaction took place slowly
• Collision theory


  • for a reaction to occur, particles need to collide
  • the amount of energy needed for particles to react is called activation energy
• Activation energy


  the minimum amount of energy needed for particles to react and start a chemical reaction
• Ways to increase the rate of reaction


  • increasing the frequency of collisions
  • increasing the energy of particles when they collide
• Factors affecting rate of reaction


  • temperature
  • concentration
  • gas pressure
  • surface area
• Increasing temperature


  • heat the container where the reaction takes place
  • particles move faster, so more frequent collisions
  • particles have more energy, so more collisions result in a reaction
• Increacing concentration of solutions


  • use a solution with more solute in the same volume of solvent
  • more reactant particles in the mixture, so collisions become more frequent
• Increase gas pressure


  • increase the number of gas particles or make the container smaller
  • less space between particles means more frequent collisions
• Increasing surface area of solids


  • Cut the solid into smaller pieces, or grind it into a powder
  • only reactant particles on the surface of a solid can collide
  • the greater the surface area, the more particles are exposed, leading to more frequent collisions
• Catalysts


  • Substances that can be added to increase the rate of reaction
  • They are not used up in the reaction
• Catalysts


  • provide a different reaction pathway that has a lower activation energy
  • this means more particles collide with enough energy to react
  • more collisions means a higher rate of reaction
• Reversible reactions


  • reactions where the products can react to produce the original products
  • represented by two arrows on top of each other
• If a forward reaction in a reversible reaction is exothermic, the backwards reaction will be endothermic
• The same amount of energy is transferred in each direction in a reversible reaction
• Equilibrium


  • in a closed system, no reactants or produts can escape
  • if a reversible reaction takes place in a closed system, it will eventually reach dynamic equilibrium
  • the point where both the forward and backwards reactions happen at the same rate
• Dynamic equilibrium

  • The point where the rate of the forwards and backwards reactions are the same
  • the reactants are still turning into the products
  • the products are still turning into the reactants
  • the rate of these two reactions are equal
  • The overall amount of reactants and products are constant
• Dynamic equilibrium


  • the amount of reactants and products in a reaction are constant, but not necessarily equal
  • the ratio is equal, not always the amount
• Reaction conditions


  • the external environments of the reaction
• Changing reaction conditions


  • changing concentration
  • changing temperature
  • changing pressure
• Le Chatalier's principle


  • at equilibrium, the amount of reactants and products is constant
  • to change these amounts, the conditions must be changed
  • the closed system will then counteract the change by favouring either the forward or backwards reaction