the rate of reaction and extent of chemical change

• what is a closed system?

  No reactants are added and no products are removed
• how is equilibrium achieved in a closed system?

  when the rate of the forward reaction is equal to the rate of the backward reaction
• what is Chatelier's Principle?

  States that if a system in equilibrium is subjected to a change in conditions then the system shifts to resist the change
• what happens to the equilibrium in an exothermic reaction?

  -If the temperature is raised the yield decreases

  -if the temperature is lowered the yield increases
• what happens to equilibrium in an endothermic reaction?

  -If the temperature is raised the yield increases

  -If the temperature is lowered the yield decreases
• what happens to the equilibrium in reactions involving gases?

  -an increased pressure favours the reaction that produces the least number of gas molecules

  -a decrease in pressure favours the reaction that produces the greater number of gas molecules
• what happens to the equilibrium if the concentration is changed?

  -the system is no longer in equilibrium

  -the system adjusts until it can reach equilibrium again
• what is a catalyst?

  A substance that increases the rate of a chemical reaction without being used up in the process
• what does a catalyst do?

  -reduces the activation energy needed

  -makes more successful collusions

  -speeds up the reaction

  -provides a surface for the molecules to attach to which increases their chances of bumping into each other
• why are catalysts important in industry?

  they reduce the amount of energy needed so they decrease costs
• what is a reversible reaction?

  a reaction that can go backwards and forwards, the products can react to produce the reactants
• how do you find the rate of reaction at a particular time on a graph?

  -draw a tangent at the time

  -find the gradient

  -the gradient is equal to the rate of reaction at that time
• what 4 factors affect the rate of reaction?

  -concentration

  -temperature

  -surface area

  -catalysts
• how does temperature affect the rate of reaction?

  An increased temperature means particles move more quickly so they collide more often with greater energy so more collusions are successful, speeding up the rate of reaction
• how does concentration affect the rate of reaction?

  An increased concentration means particles are crowded closer together and more often so there are more successful collusions, speeding up the rate of reaction. Increasing the pressure of reacting gases also increases the frequency of collusions.
• how does surface area affect the rate of reaction?

  The smaller the piece is the higher surface area to volume ratio is has so more particles are exposed and available for collusions so there are more collusions at a faster rate
• how can the rate of reaction be found?

  -measuring the amount of reactant used

  -measuring the amount of product formed

  -measuring the time it takes for a reaction mixture to change colour
• how can the rate of reaction be found by measuring the amount of reactant used?

  -if one of the products is a gas, measure the mass in grams of the reaction mixture before and after the reaction takes place and time it takes to react

  -the mass of the mixture will decrease
• how can the rate of reaction be found by measuring the amount of product formed?

  If one of the products is a gas measure the total volume of gas produced in cubic centimetres with a gas syringe and the time taken for the reaction to happen
• how can the rate of reaction be found by measuring the time taken for a colour change?

  -time how long it takes for the mixture to change colour

  -the rate of reaction = 1 divided by the time taken for a colour change
• The slope of the line gives us an idea of the rate of reaction, the steeper the slope the faster the reaction. the reaction has stopped when the line is straight
• If the product is a gas, it is measured in cm3
• le chatelliers principle states that if a reactions is at equilibrium and a change is made to the conditions then the reaction responds to counteract the change
• if you increase the pressure, the position of equilibrium will shift to the side with the smaller amount of molecules. if you decrease the pressure, the equilibrium will shift to the side with larger amount of molecules
• An exothermic reaction increases the temperature as energy is released. An endothermic reaction decreases the temperature as energy is taken in.
• If the forward reaction is exothermic and the temperature is increases, equilibrium will shift to the right as energy will need to be taken in via endothermic reaction to counteract the change.
• If the backward reaction is endothermic and the temperature decreases, equilibrium will shift to the left as energy will need to be released via exothermic reactions.
• the rate of reaction is determined by the number of successful collusions
• Catalysts increase the rate of chemical reactions but are not used up in the reaction
• catalysts allows us to carry out reactions quickly without needing to increase the temperature which saves money
• catalysts can also be resued
• catalysts increase the rate by providing an alternative pathway fort he reaction that has a lower activation energy
• The reason why we dont include catalysts in the chemical equation is because they are not used up in the reaction
• different reactions need different catalysts
• enzymes act as catalysts in living organisms
• particles in solutions can only react with the particles on the surface
• Solids with a larger surface to area volume ratio means they have more particles on the surface so there is more collusions per seconds which increases the rate of reaction