Rates of reaction

• How to measure rate of chemical reactions?

  • how fast the reactions are being used
  • how fast the products are being formed
• Rates of reaction formulas

  • quantity of products formed/time taken
  • quantity of reactants used/time taken

  measurement of quantity: grams or cm3

  measurement of time: seconds
• collision theory

  For particles to react, they have to collide with each other with sufficient energy (activation energy)
• Rates of collision dependant on

  • amount of energy particles have

  They can transfer more energy during collision

  • frequency of collisions

  The more often they collide the more successful collisions
• Temperature affecting rates of reaction

  • an increase of temp = gain more energy
  • means they move faster = collide more frequently = more successful collisions
  • collide with more energy = more likely to reach activation energy
• Concentration/pressure affecting rate of reaction

  • how many particles there are per unit of volume
  • if increase = more particles
  • collisions become more frequent
• surface area affecting rates of reaction

  • the reactant with highest surface area : volume ratio will have more area for reactions with the other reactants to take place
  • means frequency of collisions would be higher
• catalyst affecting rates of reaction

  • catalyst will lower the activation energy and give an alternative reaction pathway
  • means theres a higher proportion of successful collisions
• what does the double arrow mean in equations?

  it's a reversible reaction
• what rates do forward and backward reactions work at?

  different rates un till have equal products and reactants on each side
• What happens when a reaction is at equilibrium?

  • both reactions still happen
  • cancel each other out
  • reactants and products are not the same amount
• why does the positioning of the equilibrium change?

  • changes depending on the conditions
  • for example - adding heat encourages forward reaction as we'll have more products and equilibrium pushed to the right
  • opposite if cooled
• what system can equilibrium be reached in?

  a closed system
• why can equilibrium only be reached in a closed system?

  so no reactants or products can escape
• what way is an exothermic reaction?

  right
• what way is an endothermic reaction?

  left
• what is an endothermic reaction?

  a reaction requiring heat and absorbing it from its surroundings
• what is an endothermic reaction?

  A reaction which releases energy
• what is le chateliers principle?

  if you change the conditions of a reversible reaction then the equilibrium will shift to counteract that change
• what happens if the pressure changes in a reverse reaction?

  • if increases the equilibrium will move to the side with the least particle
  • if decreases the equilibrium will shift to the side with more particles
• what happens if the concentration changes in a reverse reaction?

  if increases the equilibrium will switch to the side with a smaller concentration and will form more of those particles.
• what happens if the temperature changes in a reverse reaction?

  • if the temp decreases the equilibrium will move to the right
  • if the temp decreases the equilibrium will move to the left