collision theory

• What is the definition of reaction rate?

  Change in concentration over time
• How can reaction rates be measured?

  By measuring reactants used or products formed
• What are three common methods to measure reaction rates?

  • Measuring a decrease in mass
  • Measuring the volume of gas produced
  • Timing how long a precipitate takes to form
• How is the rate measured for reactions producing gases?

  By observing the decrease in mass over time
• Why should the mass decrease method be conducted in a fume cupboard?

  For safety when gases are released
• How can the volume of gas produced be measured?

  Using a gas syringe over time
• What is the method for timing precipitate formation?

  Measure time until a mark is obscured
• What is the equation for the reaction between sodium thiosulfate and hydrochloric acid?

  Na2S2O3 + 2HCl ➔ 2NaCl + SO2 + S + H2O
• What happens when sodium thiosulfate and hydrochloric acid are mixed?

  A yellow precipitate of sulfur forms
• How can the rate of reaction be measured in the sodium thiosulfate and hydrochloric acid experiment?

  By timing until the black cross is obscured
• What are the steps to measure the rate of reaction in the sodium thiosulfate experiment?

  1. Measure fixed volumes of solutions
  2. Warm solutions in separate test tubes
  3. Combine solutions in a conical flask
  4. Position flask over a black cross
  5. Record time until cross is obscured
• What does the slope of a graph represent when plotting reactant amount against time?

  The reaction rate
• What is the formula for calculating the gradient of a graph?

  Gradient = change in y / change in x
• How do you calculate the average rate of reaction from a graph?

  By drawing a line of best fit
• What is the first step in calculating the average rate of reaction?

  Draw a line of best fit
• What should you do after drawing a line of best fit?

  Choose two distinct points on the line
• What is collision theory?

  Conditions for effective particle collisions
• What are the two conditions for a reaction to occur according to collision theory?

  Orientation and energy
• What is activation energy?

  The minimum energy for effective collisions
• How does activation energy affect reaction rates?

  Lower activation energy increases reaction rates
• What are the five key factors affecting reaction rates?

  • Surface area
  • Concentration
  • Pressure
  • Temperature
  • Catalyst
• How does increasing surface area affect reaction rates?

  Increases frequency of effective collisions
• What happens when concentration of reactants is increased?

  Particles collide more frequently
• How does increasing pressure affect reaction rates?

  Particles collide more frequently
• What effect does increasing temperature have on reaction rates?

  Increases kinetic energy and collision frequency
• How does adding a catalyst affect reaction rates?

  Provides a lower activation energy pathway
• Why do reactions with low activation energies occur more readily?

  Particles require less energy to react
• What is the role of heat energy in reactions with high activation energies?

  Provides extra energy for reactions to proceed