Rates and extents

• Rate of reaction: How quickly the reactants turn into the products
• 2 ways to calculate mean rate of reaction

  Quantity of reactant used / time taken

  Quantity of product formed / time taken
• Volume of gas produced experiment + rate of reaction

  Mixture of reactants is connected to a gas syringe OR an upside down measuring cylinder, as the reaction happens, gas is collected

  Rate = volume of gas produced (cm^3) / time taken (s)

  Rate = cm^3/s
• Change in mass experiment + rate of reaction


  Mixture of reactants is placed onto balance, as the reaction happens the gas produced goes out and mass decreases

  Rate = Change in mass (g) / time taken (s)

  Rate = g/s
• Change in colour experiment

  Place reactants over a white piece of paper with a cross on, time how long it takes for the cross not to be visible

  Quicker its not visible, quicker the reaction
• Steep gradient on a graph means: reaction happened quickly
• Shallow gradient on a graph means: reaction happened slowly
• Calculating mean rate of reaction from a graph

  Change in mass / Change in time (Mean rate only applies between the points measured)
• What has to happen for a reaction to occur?

  Particles have to collide
• 2 ways to increase rate of reaction

  Increase frequency of collisions

  Increase energy of the particles when they collide
• Why do particles need to have energy to react?

  If they do not collide with enough force they will just bounce apart
• Increasing rate of reaction - increase the temperature

  Heat the container that the reactants are in

  • Particles move quicker and collide more
  • Particles have more energy so react more when they collide
• Increasing rate of reaction - increase concentration

  Use a solution with more solute but same amount of solvent

  • More reactant particles, collisions more frequent
• Increasing rate of reaction - Increase pressure of gas

  Use more gas or smaller container

  • Less space between particles = more frequent collisions
• Increasing rate of reaction - Increase surface area of solids

  Cut solid into smaller pieces or grind into powder

  • larger surface are of reactant particles to collide and react
• Catalyst: Specific substrate that can increase the rate of reaction
• Equilibrium: When a reversable reaction has an unchanging ratio of products to reactants
• Reversable reaction

  The products can produce the original reactants

  Same amount of energy is produced in either direction
• The same amount of energy is produced in either direction of the reversable reaction
• What happens if a reversable reaction is carried out in a closed system?

  It will eventually reach dynamic equilibrium
• Dynamic equilibrium - A point in time where the forward and reverse reactions have the same rate
• What happens at dynamic equilibrium?

  Reactants are still turning into products

  Products are still turning back into reactants

  The rates of these 2 processes are equal
• At dynamic equilibrium the amount of reactant and products are constant but not necessarily equal
• How to change the conditions of a reaction in a closed system? (3)

  Changing the concentration of one of the substances

  Changing the temperature of the vessel its in

  Changing the pressure inside the vessel
• Le Chatelier's principle

  In order to change the amounts of reactant and product at equilibrium, the conditions must be changes, the closed system counteract the change by favoring either the forward or reverse reaction
• Changing conditions - Decreasing concentration of product

  Effect - Favours the forward reaction

  Why - Opposes the change by making less reactant and more product
• Changing conditions - Increase concentration of product

  Effect - Favours the reverse reaction

  Why - opposes the change by making more reactant and less product
• Changing concentrations - Decrease concentration of reactant

  Effect - Favour the reverse reaction

  Why - Opposes the change by making more reactant and less product
• Changing conditions - Increase concentration of reactant

  Effect - Favours the forward reaction

  Why - Opposes the change by making more product and less reactant
• The effect of changing temperature depends on which direction is exothermic and which direction is endothermic
• Changing conditions - Increase temp of surroundings

  Effect - Favours the endothermic reaction

  Why - Opposes the change by decreasing temp of surroundings
• Changing conditions - Decrease temp of surroundings

  Effect - Favours the exothermic reaction

  Why - Opposes the change by increasing the temp of the surroundings
• The effect of changing the pressure depends on which side of the reaction has more molecules of gas
• Changing conditions - increase the pressure

  Effect - Favours the reaction that results in fewer molecules

  Why - opposes the change by decreasing the number of molecules within the vessel, decreasing the pressure
• Changing conditions - Decreasing the pressure

  Effect - Favours the side which results in more molecules

  Why - Opposes the change by increasing the number of molecules within the vessel, increasing the pressure