The rate and extent of chemical change

• How is the rate of reaction calculated?

  Rate of reaction = amount of reactant used or product formed / time
• What is the formula for rate of reaction in moles?

  Rate of reaction (mol/s) = moles of reactant used or product formed / time
• What are the various units for rate of reaction?

  g/s, cm³/s, mol/s
• Name three common ways of measuring the rate of reaction.

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

  • Place reaction flask on a balance
  • Record decrease in mass over time intervals
  • Plot graph of mass vs time
• How do you measure the rate by monitoring the volume of a gas?

  • Connect gas syringe to reaction flask
  • Measure volume of gas formed over time intervals
  • Plot graph of volume vs time
• How do you measure the rate by monitoring the disappearance of a cross?

  • Mark a cross on paper
  • Place reaction flask on the cross
  • Measure time taken for cross to disappear
• 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
• State five factors affecting the rate of a chemical reaction.

  • Concentration of reactants<br>- Pressure of gases<br>- Surface area<br>- Temperature<br>- Catalysts
• What is the collision theory?

  Reactions occur when particles collide with sufficient energy
• Describe the effect of increasing temperature on the rate of reaction.

  • Higher temperature = faster reaction
  • Increased kinetic energy of particles
  • More frequent and energetic collisions
  • No direct proportionality between rate and temperature
• Describe the effect of increasing concentration on the rate of reaction.

  • Higher concentration = faster reaction
  • More reactants lead to more frequent collisions
• Describe the effect of increasing pressure of a gas on the rate of reaction.

  • Higher pressure = faster reaction
  • More gas molecules in the same volume
  • Increased frequency of collisions
  • Volume and pressure are inversely proportional
• Describe the effect of increasing surface area on the rate of reaction.

  • Smaller pieces = greater surface area
  • More frequent collisions increase reaction rate
  • Example: magnesium powder reacts faster than a block
• What is a catalyst and how does it work?

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

  It lowers the activation energy of the reaction
• What is an enzyme?

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

  A reversible reaction can produce original reactants from products
• When is dynamic equilibrium reached?

  When forward and reverse reactions occur at the same rate
• Describe Le Chatelier’s Principle.

  System responds to counteract changes and restore equilibrium
• Describe the effect of changing the concentration of reactants and products on equilibrium.

  • Changing concentration disrupts equilibrium
  • Increased reactant concentration forms more products
  • Decreased product concentration forms more reactants
• Describe the effect of changing temperature on the position of equilibrium.

  • Increased temperature favors endothermic reactions
  • Decreased temperature favors exothermic reactions
• Describe the effect of changing pressure on the position of equilibrium.

  • Increased pressure shifts equilibrium to fewer gas molecules
  • Decreased pressure shifts equilibrium to more gas molecules
  • No effect if gas molecules are equal on both sides
• Describe the effect of a catalyst on the position of equilibrium.

  • No effect on equilibrium position
  • Speeds up both forward and backward reactions equally