rate and extent of chemical change

• what is rate of reaction?

  The speed at which a chemical reaction takes place.
• factors that effect rates of reaction :

  • temperature
  • concentration of solution or the pressure of gas
  • surface area
  • presence of a catalyst
• increasing temp:

  • particles move faster
  • collisions are more frequent
  • faster they move the more energy they have so more collisions will ahve enough energy to create a reaction
• increasing concentration/ pressure:

  • more particles in the same volume
  • collisions are more frequent
• increasing surface area:

  • increased surface area to volume ratio
  • for the same volume the particles around it will have more area to work on
  • collisions are more frequent
• rates of reaction from a graph:

  • product formed or amount of reactant used on y-axis
  • time on x-axis
  • mean rate of reaction = change in y/ change in x
  • use a tangent to work out rate of reaction at a specific point
• reversible reactions:

  • as reactants react their concentrations fall so forward reaction slows down
  • as more products are made and concentrations rise the backwards reaction will speed up
  • after a while the forward reaction will be going the same rate as the backward one (system is at equilibrium)
• in reversible reactions if the reaction is endothermic in one direction it will be exothermic in the other
• equilibrium:

  • when a reaction is at equilibrium it doesnt mean the amounts of reactants and products are equal
  • if equilibrium lies to the right the concentration of products is greater than the reactants
  • if equilibrium lies to the left the concentration of ractants is greater than the products
• what is the position of equilibrium effected by ?

  temperature, pressure (gasses) and concentration of reactants and products
• what is Le Chatelier's principle?


  if you change the conditions of a reversible reaction at equilibrium the system will try to counteract that change
• if we increase pressure on a reversible reaction at equilibrium the position of equilibrium shifts to the side with the smaller number of particles