Rates of reaction

• Collision theory states that for particles to react, they have to collide with sufficient energy.
• The minimum amount of energy required for a reaction to take place is called the activation energy.
• When considering how a condition will affect the rate of reaction, you have to consider how it will affect the frequency of collisions, and/or the energy of the particles.
• The line is steepest at the start of a reaction because there are a lot of reactants.
• What should you be able to describe by the end of this video?

  The effect of pressure on equilibrium
• What happens to a system at equilibrium when conditions change?

  The system responds to counteract the change
• What principle explains the response of a system at equilibrium to changes?

  Le Chatelier's principle
• What is the focus of this video regarding reversible reactions?

  The effect of pressure on reversible reactions
• What does the pressure of a gas depend on?

  The number of molecules present
• How does the number of molecules affect gas pressure?

  More molecules result in higher pressure
• In the reaction of nitrogen and hydrogen to form ammonia, how many molecules are on the left side?

  Four molecules
• How many molecules of ammonia are produced in the reaction?

  Two molecules
• What happens to the equilibrium position if pressure is increased in a reaction with fewer molecules on the right side?

  The equilibrium shifts to the right side
• What happens to the equilibrium position if pressure is decreased in a reaction with more molecules on the left side?

  The equilibrium shifts to the left side
• In the reaction between iodine and hydrogen, how many molecules are present on both sides?

  Two molecules on each side
• What is the effect of changing pressure on the equilibrium position when the number of molecules is the same on both sides?

  Changing pressure has no effect
• What are the rules regarding pressure effects on reversible reactions?

  • Increase pressure: equilibrium shifts to fewer molecules
  • Decrease pressure: equilibrium shifts to more molecules
• What is the reaction between nitrogen and hydrogen producing?

  • Produces ammonia
  • Reaction is reversible
• What is the reaction between iodine and hydrogen producing?

  • Produces hydrogen iodide
  • Reaction is reversible
• Where can you find more questions on reversible reactions?

  • In the revision workbook linked above
• If the concentration of A increases, what will happen to the forward and reverse reactions?

  forward reaction is favoured to decrease concentration of A
• What does it mean when a chemical reaction is at equilibrium?

  Amounts of reactants and products remain constant over time.
• How does the concentration of A change when the forward and reverse reactions occur?

  • When concentration of A decreases, the forward reaction is favoured
  • When concentration of A increases, the reverse reaction is favoured
• How do the forward and reverse reactions behave at equilibrium?

  They occur at equal rates, maintaining constant amounts.
• What is the definition of equilibrium in a chemical reaction?

  Equilibrium occurs when forward and reverse reactions happen at equal rates.
• How do the changes in concentration of A affect the forward and reverse reactions in this chemical equation?

  Increase in A favours forward reaction, decrease in A favours reverse reaction
• Le Chatelier's principle states that if you change the conditions of a reversible reaction, the position of equilibrium will shift to try and counteract the change.
• 3 factors that affect the position of equilibrium

  • Concentration
  • Pressure
  • Temperature
• An increase in pressure moves the position of equilibrium to whichever side has the smaller number in gas particles