C6 - the rate and extent of chemical change

• What greatly influences the rates of reaction?

  The chemical reactants
• What does the rate of a chemical reaction measure?

  How fast reactants change into products
• How does the steepness of a graph relate to the rate of reaction?

  Steeper lines indicate faster reactions
• What happens to the graph when reactants are used up?

  The line becomes flat
• What is collision theory?

  It explains how reactions occur through collisions
• What two factors affect the rate of a chemical reaction according to collision theory?

  Collision frequency and energy transferred
• What is activation energy?

  The minimum energy needed for a reaction
• How does increasing the concentration affect the rate of reaction?

  It increases the number of collisions
• What are the factors affecting the rates of reaction?

  • More collisions increase the rate
  • Increasing temperature increases the rate
  • Increasing concentration or pressure increases the rate
  • Increasing surface area increases the rate
  • Using a catalyst increases the rate
• Which reaction would have the fastest rate: 2 mol/dm³ HCl with excess ethanoic acid or 4 mol/dm³ HCl with excess ethanoic acid?

  4 mol/dm³ HCl with excess ethanoic acid
• Which reaction would have the fastest rate: a 2 g solid strip of magnesium with water or 2 g of powdered magnesium with water?

  2 g of powdered magnesium with water
• What are the three methods to measure the rate of a reaction?

  1. Precipitation and colour change
  2. Change in mass (gas given off)
  3. Volume of gas given off
• What is a disadvantage of measuring change in mass for a reaction?

  Gas is released into the room
• What happens when gas is produced during a reaction?

  The volume of gas indicates the reaction rate
• How can you find the mean reaction rate from a graph?

  Calculate the gradient of the line
• How do you find the reaction rate at a specific point on a graph?

  Draw a tangent at that point
• What is dynamic equilibrium in reversible reactions?

  Rates of forward and reverse reactions are equal
• How does heating affect the position of equilibrium in a reversible reaction?

  It moves the equilibrium to the right
• What happens in an endothermic reaction?

  Energy is absorbed from the surroundings
• What happens in an exothermic reaction?

  Energy is released to the surroundings
• What does Le Chatelier's Principle state?

  • Reversible reactions try to counteract changes
  • Changes can be in temperature, pressure, or concentration
• What is the term for how quickly a reaction happens?

  Rate of reaction
• How is the rate of reaction defined?

  Change in quantity divided by time
• What can the quantity in a rate of reaction refer to?

  Mass or volume of gas produced
• What does the mean rate of reaction indicate?

  Average rate over the time measured
• Describe an experiment to measure the rate of reaction using hydrochloric acid and sodium thiosulfate.

  • Use a conical flask over a paper with a cross.
  • Observe the solution turning cloudy (increased turbidity).
  • Stop timing when the cross is no longer visible.
  • Repeat at different temperatures.
• What happens to the time taken for a reaction as temperature increases?

  It takes less time
• How can the volume of gas produced be measured in a reaction?

  • Use a gas syringe connected to the reaction vessel.
  • Record the volume as it fills up.
  • Plot a graph with quantity on the y-axis and time on the x-axis.
• What does a graph of gas volume against time typically look like?

  Starts steeply, then levels out
• How can the rate of reaction be determined from a graph?

  By drawing a tangent at a point
• What is the formula to find the rate of reaction using a tangent?

  Change in quantity divided by time
• What factors can increase the rate of a reaction?

  • Increasing concentration of reactants
  • Increasing pressure of gas reactants
  • Increasing surface area of solid reactants
• Why does increasing temperature increase the rate of reaction?

  Particles move faster and collide more often
• What is activation energy?

  Energy needed for particles to react
• What is the role of a catalyst in a reaction?

  Reduces activation energy needed
• What happens to a catalyst during a reaction?

  It is not used up
• What are reversible reactions?

  • Products can revert to original reactants.
  • Example: Haber process (ammonia production).
  • Both forward and reverse reactions occur continuously.
• What occurs in a closed system regarding reversible reactions?

  Rates of forward and reverse reactions equalize
• What does it mean when equilibrium is reached?

  No overall change in quantities
• What does Le Chatelier's principle state?

  System adjusts to counteract changes