Rates of Reaction

• What does the rate of a reaction measure?

  How quickly a reactant is used or product formed
• What are the requirements for a chemical reaction to occur according to collision theory?

  • Reactant particles must collide
  • Particles must have enough energy to react
• What is a successful collision?

  A collision that produces a reaction
• What is activation energy?

  The minimum energy needed for a successful collision
• How do reactant particles behave during a reaction?

  They collide with each other
• What are the methods to determine the rate of a reaction?

  • Measuring mass change
  • Measuring volume change
  • Analyzing graphs of mass or volume against time
• How is the mean rate of reaction calculated using reactants?

  $\text{mean rate} =$$\frac{\text{quantity of reactant used}}{\text{time taken}}$
• How is the mean rate of reaction calculated using products?

  $\text{mean rate} =$$\frac{\text{quantity of product formed}}{\text{time taken}}$
• When is measuring mass useful in a reaction?

  • When carbon dioxide is a product
  • Not suitable for hydrogen or light gases
• What are the common units for measuring rate of reaction by mass?

  g/s or g/min
• When is measuring volume useful in a reaction?

  • When a gas leaves the reaction container
  • Measured using gas syringe or burette
• How can the rate of reaction be analyzed graphically?

  • Plot mass or volume of product against time
  • Steeper line indicates greater rate of reaction
• What does a horizontal line on a reaction rate graph indicate?

  The reaction has finished
• What does the gradient of the line on a reaction rate graph represent?

  The rate of reaction
• How does the steepness of the line relate to the rate of reaction?

  Steeper lines indicate greater rates of reaction
• What increases the rate of reaction?

  The frequency of successful collisions
• What happens to reactant particles when concentration or pressure increases?

  They become more crowded
• How does increasing concentration or pressure affect collision frequency?

  It increases the frequency of collisions
• What remains unchanged when concentration or pressure increases?

  The mean energy of the particles
• What happens to the frequency of successful collisions when collision frequency increases?

  It also increases
• How can the rates of two or more reactions be compared?

  • Using a graph of mass or volume of product formed against time
  • Curved lines represent reaction data
  • Tangents indicate the rate of reaction
• What do the straight dashed lines at the start of the reactions represent?

  Tangents to the reaction curve
• What does a steeper tangent on a graph indicate?

  A faster reaction rate
• What happens to the steepness of the tangent as the reaction progresses?

  It decreases, indicating a slowing reaction
• How do you calculate the rate of reaction from a tangent's gradient?

  Using the change in mass or volume over time
• What is the equation for calculating the rate of reaction?

  rate of reaction = change in mass or volume / change in time
• What happens to the surface area to volume ratio when a large lump is divided into a powder?

  It increases
• What remains constant when a large lump is ground into a powder?

  Total volume stays the same
• How does dividing a lump affect the area of exposed surface?

  The area of exposed surface increases
• What is the relationship between surface area to volume ratio and reaction rate?

  A higher ratio increases the reaction rate
• What happens to the frequency of collisions when the surface area to volume ratio increases?

  The frequency of collisions increases
• Does the mean energy of particles change when the surface area to volume ratio increases?

  No, it does not change
• What does a graph of mass or volume of product against time show?

  It compares the rates of reactions
• What does a steeper line on a reaction graph indicate?

  A faster reaction rate
• What does the gradient of the line on a reaction graph represent?

  The rate of reaction
• How does the reaction time differ when using a powder compared to a lump?

  The powder finishes sooner
• What increases the rate of reaction?

  The frequency of successful collisions
• What happens to reactant particles when temperature increases?

  They move more quickly
• How does temperature affect the energy of particles?

  The energy of the particles increases
• What is the effect of increased temperature on successful collisions?

  The frequency of successful collisions increases