Topic 6 - Rate and extent of chemical change

• How is the rate of reaction calculated?

  Rate of reaction = amount / time
• What is the formula for rate of reaction in moles?

  Rate of reaction (mol/s) = moles / time
• What are the general units for rate of reaction?

  Mass/time, volume/time, moles/time
• What are three common ways to measure the rate of reaction?

  • Loss in mass of reactants
  • Volume of gas produced
  • Time for a solution to become opaque
• How do you measure the rate of reaction by monitoring mass loss?

  Place the reaction flask on a balance. In these reactions (e.g. metal carbonate +

  acid) a gas is given off, so record the decrease in mass in time intervals (note

  hydrogen is too light). Plot a graph of mass vs time.
• How do you measure the rate of reaction by monitoring gas volume?

  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.
• How do you measure the rate of reaction by monitoring the disappearance of a cross?

  Time taken for a cross to be concealed
• How do you find the rate of reaction at time t from a graph?

  Find the tangent at time t on the curve
• What does the gradient of the tangent represent on a rate of reaction graph?

  It indicates how fast the reaction proceeds
• What are five factors affecting the rate of a chemical reaction?

  Concentration, pressure, surface area, temperature, catalysts
• What is the collision theory?

  Reactions occur when particles collide with sufficient energy
• How does increasing temperature affect the rate of reaction?

  Higher temperature increases kinetic energy and collision frequency
• Is there a direct relationship between rate and temperature?

  No, they are not directly proportional
• How does increasing concentration affect the rate of reaction?

  More reactants lead to more frequent collisions
• How does increasing pressure affect the rate of reaction for gases?

  Increases frequency of collisions, similar to concentration
• What is the relationship between volume and pressure in reactions?

  Increasing volume retards the reaction
• How does increasing surface area affect the rate of reaction?

  Smaller pieces increase surface area and collision frequency
• What is a catalyst and how does it affect reactions?

  A catalyst speeds up reactions without being used up
• How does a catalyst change the reaction profile?

  It provides a pathway with lower activation energy
• What is an enzyme?

  An enzyme is a biological catalyst
• What is a reversible reaction?

  Products can react to form original reactants
• When is dynamic equilibrium reached?

  When forward and reverse reactions occur at the same rate
• What is Le Chatelier’s Principle?

  System responds to counteract changes and restore equilibrium
• How does changing reactant concentration affect equilibrium?

  Changes cause shifts until equilibrium is restored
• How does changing temperature affect equilibrium position?

  Increased temperature affects product amounts differently
• How does changing pressure affect equilibrium position in gas reactions?

  Shifts towards side with fewer gas molecules
• What is the effect of a catalyst on equilibrium position?

  No effect, just speeds up reactions