The rate and extent of chemical change

• Name 3 ways of measuring rate of reaction:


  Loss in mass of reactants

  Volume of gas produced

  Time for a solution to become opaque
• Describe measuring the rate by monitoring mass loss:

  Place the reaction flask on a balance

  In these reactions a gas is given off so record the decrease in mass in time intervals

  Plot a graph of mass vs time
• Describe measuring the rate by monitoring the volume of a gas:

  Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals

  Plot a graph of volume vs time
• Describe measuring the rate by monitoring the disappearance of a cross:

  Take a peice of paper and mark a cross on it

  Put the reaction flask on this cross

  Mix the reagents, and measure how long it takes for a cloudy mixture to conceal a cross
• State 5 factors affecting the rate of a chemical reaction:

  Concentration of reactants

  Pressure of gases (volume)

  Surface area

  Temperature

  Catalysts
• What is the collision theory?

  Chemical reactions can only occur when reacting particles collide with each other with sufficient energy (activation energy)
• Describe the effect of increasing temp on the rate of reaction:

  A temp increases, kinetic energy of particles increases-> they move faster so collide more frequently
• Describe the effect of increasing concentration on the rate of reaction:

  Concentration increases-> faster reaction

  More reactants-> more frequent collisions
• Describe the effect of increasing pressure of a gas on the rate of reaction:

  Increasing the pressures of gases is the same as increasing concentration

  -> It increases the number of gas molecules in the same volume and so increases the frequency of collisions and therefore increases the rate of reaction

  Note that volume and pressure are inversely proportional to eachother
• Describe the effect of increasing surface area:

  If solid reactants are in smaller pieces, they have a greater surface area

  Increasing the surface area of solid reactants increases the frequency of collisions and so increases rate of reaction
• How do catalysts affect the reaction profile?

  A catalyst changes the rate of reaction but is not used

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

  The reaction profile for a catalysed reaction will have a lower maximum of the curve
• When is dynamic equilibrium reached?

  In a closed system, when the forward and reverse reactions occur at the same rate and the concentration of reactants and products remain constant
• Describe Le Chatelier’s Principle:

  If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium
• Describe the effect of changing concentration. Of reactant and product on the position of the equilibrium:

  If the concentration of a reactant is increased, more products will be formed

  If the concentration of a product is decreased, more reactants will react until equilibrium is reached again
• Describe the effect of changing temp on the position of the equilibrium:

  If temp is increased:

  The amount of products increases for an endothermic reaction

  The amount of products decreases for an exothermic reaction
• Describe the effect of changing pressure on the position of the equilibrium:

  Increase in pressure causes the equilibrium to shift towards the side with the smaller number of molecules

  Decrease in pressure causes the equilibrium to shift towards the side with the larger number of molecules

  Pressure has no effect on the reactions where the number of gas molecules are equal on both sides of the equation
• Describe the effect of a catalyst on the position of the equilibrium:

  No effect

  It speeds up both forward and backward reactions equally