Rate of reaction

• 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 be measured to determine the rate of reaction?

  Quantity of reactant used or product formed
• What does the mean rate of reaction indicate?

  It averages the rate over the measurement period
• What is an experiment to measure the rate of reaction using hydrochloric acid and sodium thiosulfate?

  • Reactants: Hydrochloric acid and sodium thiosulfate
  • Setup: Conical flask over a cross on paper
  • Observation: Solution turns cloudy (increased turbidity)
  • Stop timer when cross is no longer visible
  • Repeat at different temperatures
• What happens to the time taken for a reaction as temperature increases?

  It decreases
• How can the volume of gas produced be measured in a reaction?

  • Use a gas syringe connected to the reaction vessel
  • Record the volume of gas produced over time
  • Graph: Quantity on y-axis, time on x-axis
  • Graph shape: Starts steep, then levels out
• What does a leveling out of the graph indicate?

  The reaction has completed
• How do you find the rate of reaction at a specific time from a graph?

  Draw a tangent at that point
• What is the formula to calculate the rate of reaction using a tangent?

  Change in quantity divided by change in 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 (crushing)
  • Increasing temperature
  • Adding a catalyst
• Why does increasing temperature increase the rate of reaction?

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

  The minimum energy needed for a reaction to occur
• How does a catalyst affect activation energy?

  It reduces the 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 (hydrogen and nitrogen to ammonia)
  • In a closed system, both reactions occur continuously
  • Equilibrium reached when forward and reverse rates are equal
• What does it mean when a system is at equilibrium?

  No overall change in quantities of reactants/products
• What does Le Chatelier's principle state?

  System adjusts to counteract changes
• What happens if pressure is increased in a reaction with more moles on the left side?

  It favors the forward reaction
• What occurs when the pressure is reduced in a reaction?

  It shifts the equilibrium to the left
• How does concentration affect equilibrium in solutions?

  Removing molecules shifts equilibrium towards that side
• What does increasing temperature favor in an endothermic reaction?

  It favors the reverse reaction
• What does decreasing temperature favor in an exothermic reaction?

  It favors the forward reaction
• What is the relationship between forward and reverse reactions in reversible reactions?

  • If forward reaction is exothermic, reverse is endothermic
  • If forward reaction is endothermic, reverse is exothermic
  • Energy changes are linked to reaction direction