the rate and extent of chemical change

• rate of a chemical reaction

  how fast the reactants are changed into products
• rate of reaction graphs

  steeper line - faster the rate of reaction
• collision theory

  the collision frequency of reacting particles; the more collisions the faster the reaction is
• activation energy

  the minimum amount of energy that particles need in order to react
• rate of reaction depend on 4 things

  temperature; concentration; surface area; presence of a catalyst
• catalyst

  a substance that speeds up a reaction
• mean rate of reaction

  rate of reaction = amount of reactant used or amount of product formed / time
• measure rate of reaction: precipitation and colour change


  the product is precipitate which clouds the solution. You can observe a mark through the solution and measure how long it takes for it disappear
• measure rate of reaction: change in mass


  measuring the speed of a reaction that produces a gas can be carried out using a mass balance; as gas is released, the mass disappearing is measured on the balance. the quicker the reading drops, the faster the reaction
• measure rate of reaction: volume of gas given off

  involves the use of a gas syringe; the more gas given off during a given time interval, the faster the reaction
• Magnesium and HCl react to produce H2 gas


  start by adding a set volume of dilute hydrochloric acid to a conical flask and carefully place on a mass balance; add magnesium ribbon to the acid and plug the flask with cotton wool; start the stopwatch and record the mass on the balance; take reading of the mass at regular intervals; plot it on a graph and repeat with different concentrated solutions
• sodium thiosulfate and HCl produce a cloudy precipitate


  start by adding a set volume of dilute thiosulfate to a conical flask; place the flask on paper with a black cross drawn on it; add some dilute HCl to the flask and start the stopwatch; the cross will disappear through the cloudy sulphur; plot the timing and repeat with either reactant at different concentrations
• mean rate from a graph

  change in y/ change in x
• reversible reactions will reach equilibrium

  at equilibrium both reactions are still happening but there's no overall effect. Equilibrium is only reached if the reversible reaction takes place in a closed system. A closed system means that none of the reactants and products can escape and nothing can get in
• position of equilibrium

  if the equilibrium lies to the right, the concentration of products is greater than the reactant's. if the equilibrium lies to the left, the concentration of reactants is greater than the product's
• position of equilibrium depend on:

  temperature; pressure (only affects equilibria involving gases); concentration of reactants and products
• Le Chatelier's principle

  the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change