rate of reaction

• rate of reaction


  the speed of different chemical reactions varies hugely

  some reactions are very fast and other are very slow

  fast = exposive

  slow = rust
• rate = quantity of reactions used up / time taken

  rate = quantity of products formed/time taken
• units for reactions


  g/s or g/min -> if product is weighed

  $cm^3\$/ s or cm$^3$/min -> gas

  mol/dm$^3$
• reactions particles and collisions


  reactions between particles take place when particles collide (with enough energy) so that bonds are broken and new bonds can be formed

  reactions stop when one of the reaction is used up - the reactant runs out is called the limiting factor - the other reactants is in excess
• rate and graphs


  the faster the rate the steeper the graph

  as the reaction takes place of the reactants get used up and rates slow down

  when the graph is horizontal (plateaus) the reaction has stopped - no more product is being made

  A) faster reactions

  B) slow reactions

  C) time

  D) total mass of products

  
• reactions do not proceed at a steady rate - start off fast and then get slower until the stop

  as the reaction continues, the concentration of reactants decreases - this reduces the frequency of successful collisions between particles and makes the rate slow down
• rate of reactions

  for a specific point on the curve - draw a tangent then $\frac{\Delta y}{\Delta x}$

  A) Y/X

  
• how to measure rate


  1. volume of gas produced - syringe
  2. measure the loss of mass using a balance
  3. time how long it tales for colourless solutions to become opaque
• volume of gas produced syringe


  magnesium and hydrochloric acid react - the gas produced goes up the tube and is collected in the syringe

  A) gas syringe

  B) magnesium

  C) hydrochloric acid

  D) glass tube

  E) bung

  
• time how long it takes for a colourless solution to turn opaque


  place a flask on a piece of paper with an X drawn on it

  time how long it takes for the solution to turn opaque (can't see the cross)

  A) sodium thiosulphate and hydrochloric acid

  B) cross on white tile

  
• how does temperature effect rate of reaction


  increasing the temperature increases the rate of reactions

  by increasing the temperature, there is an increase in kinetic energy

  this increases the frequency of successful collisions
• how does concentration effect rate of reactions


  By increasing the concentration of sodium thiosulphate, less time is needed for the reaction to take place

  this is because there are more reacting particles in the same volume

  this increases the frequency of successful collisions
• factors that effect the rate of reaction


  1. concentration - more reacting particles in the same volume
  2. pressure - same volume of particles in less space
  3. temperature - particles have more energy
  4. surface area - more particles on the surface area
  5. catalysts - surface for particles to stick too - provide a different pathway

  all increase the frequency of successful collisions
• catalysts


  increases the rate of reaction

  they are not used up - can be used again

  only small amount is needed

  specific to a particular reaction

  produce the same volume product quicker
• catalyst reaction profiles


  catalysts increases the rate of reaction by providing a different pathway for the reaction that has lower activation energy

  they also provide a surface for the particles to stick to

  A) low Eact - with catalysts

  B) Eact

  C) Reactants

  D) Products

  
• reversable reactions


  a reversable reactions is a reaction that can go either way as the products of one reaction acts as the reactants in the opposite reaction

  A) symbol

  B) <- products

  C) reactants <-

  D) reactants ->

  E) products ->

  
• reversible reaction - heating copper sulphate


  the change of blue hydrated copper sulphate to white anhydrous copper sulphate is one of the most commonly know reversible reaction

  $hydrated\ copper\ sulphate\ \leftarrow heat\rightarrow\ anhydrous\ copper\ sulphate\ +$$\ steam$

  $CuSO_45H_2O\ \leftrightarrow\ CuSO_4+$$5H_2O$
• energy 


  if a reversable reaction is exothermic in one direction, it is endothermic in the opposite

  the same amount of energy is transferred in each case
• equilibrium


  a closed system is needed - reactions and products can't escape

  reached when the reactants are making products at the same rate the products are making reactants

  overall there is no change in the amount of products and reactants

  in a reversible reaction the forward and backward reaction are continuously taking place (unnoticed) a state of dynamic equilibrium has been reached
• factors that effecting equilibrium 


  temperature

  concentration

  pressure (gas)
• equilibrium


  is a system is at equilibrium and changed is made to any of the conditions then the system responds to counteract the change

  the effects changing conditions on a system at equilibrium can be predicted using Le Chatelier Principle
• Le Chatelier Principle - temperature


  increasing the temperature shifts the equilibrium in the endothermic reactions (system cools down)
• Le Chatelier Principle - concentration


  increasing the concentration of a substance shifts the equilibrium in the direction that produces less of that substance
• Le Chatelier Principle

  increasing the pressure shifts the equilibrium in the direction that produces less moles of gas