chap 10 rate of reactions

• what are some ways to measure the appearance or disappearance of substances by measuring ?

  • volume of gas produced in the reaction
  • change in mass of a reactant or product
• describe how the rate of reaction changes over time

  1. at the start, the gradient of the graph is the steepest so the rate of reaction is the fastest
  2. this is due to there being the largest mass of reactants to react with each other
  3. as the reaction progresses, the gradient of the graph becomes gentler, telling us that the rate of reaction decreases with time
  4. this is due to there being lesser amounts of reactants to react with each other
  5. at _ min, the gradient approaches zero, telling us that the reaction has completed and the volume/ mass of product/ reactant has remained constant

  
• is the gradient of the graph positive or negative when measuring products ?

  positive
• is the gradient of the graph positive or negative when measuring reactants ?

  negative
• what is effective collision ?

  it is when a chemical reaction occurs between particles that collide
• what are the factors affecting the rate of reaction ?

  • concentration
  • pressure
  • particle size
  • temperature
  • catalyst
• how does concentration have an effect on rate of reaction ?

  • the higher the concentration of reactants, the higher the number of particles in a given volume
  • this causes the number of collisions per unit time to increase, and hence the frequency of effective collisions increase
  • this increases the rate of reaction
• what is the relationship between concentration and rate of reaction ?

  an increase in concentration of reactants increases the rate of reaction
• how does the change in concentration of the limiting reagent affect the amount of products formed ?

  the higher concentration of the limiting reagent, the more products are formed
• how does the change in concentration of the excess reagent affect the amount of products formed ?

  it does not affect the amount of products formed
• when is a collision effective ?

  it is when reactant particles have sufficient energy to overcome the activation energy of the reaction and collide in the proper orientation to bring about a reaction
• what is the relationship between pressure and the rate of reaction ?

  an increase in the pressure of gaseous reactants results in an increase in the rate of reaction
• what state does pressure only work on ?

  reaction of gases
• how does pressure affect the rate of reaction ?

  • when pressure is high, reacting particles are closer to each other
  • this increases the number of collisions per unit time, increasing frequency of effective collision
  • this increases the rate of reaction
• how can pressure be increased ?

  by reducing the volume that the reacting particles occupy
• what is the relationship between the particle size and rate of reaction ?

  an increase in the particle size of solid reactants result in an decrease in the rate of reaction
• how does the particle size have an effect on the rate of reaction ?

  • as the particle size of a reactant increases, its surface area to volume ratio decreases
  • this decreases the number of collisions per unit time and hence frequency of effective collisions decrease
  • this decreases the speed of reaction
• what is the relationship between temperature and rate of reaction ?

  an increase in the temperature of reactants results in an increase in the rate of reaction
• how does temperature have an effect on the rate of reaction ?

  • when the temperature increases, kinetic energy of reacting particles increases, causing particles to move faster and more vigorous
  • this increases the number of collisions per unit time and hence the frequency of effective collisions is higher
  • this increases the speed of reaction
• what are catalysts ?

  they increase the rate of chemical reactions without being chemically changed at the end of the reaction
• what are some characteristics of catalysts ?


  • increase reaction rates but not the yield
  • not used up in the reaction
  • they are selective in the reactions that they catalyse
  • impurities can poison them
  • physical appearance may change but they remain chemically the same
  • provide an alternative pathway with a lower activation energy for the reaction
• what is the relationship between presence of catalyst and rate of reactions ?

  with the presence of catalyst, the rate of reaction increases
• how does the presence of catalyst affect the rate of reaction ?

  • catalyst provide an alternative pathway of lower activation energy for the reaction to occur
  • this causes more reactant particles to have energy greater than or equal to activation energy
  • this increases frequency of effective collisions, hence increasing the rate of reaction
• what are enzymes ?

  biological catalysts
• what characteristics do enzymes have ?

  • made of protein
  • temperature- sensitive
  • pH- sensitive
  • specific catalytic action