Topic 6: rate of chemical change

• How is the rate of reaction calculated?

  Rate of reaction = amount / time
• What is the formula for rate of reaction in moles?

  Rate of reaction (mol/s) = moles / time
• What are three common ways of measuring the rate of reaction?

  • Loss in mass of reactants
  • Volume of gas produced
  • Time for a solution to become opaque
• What is the general expression for the units of rate of reaction?

  Generally, mass/time, volume/time, moles/time
• How is the rate of reaction measured by monitoring mass loss?

  Record mass decrease over time intervals
• How is the rate of reaction measured by monitoring gas volume?

  Measure gas volume formed over time intervals
• How is the rate of reaction measured by monitoring the disappearance of a cross?

  Time taken for a cross to be concealed
• How do you find the rate of reaction at time t from a graph?

  Find the tangent to the curve at time t
• What does the gradient of the tangent represent on a rate of reaction graph?

  It indicates how fast the reaction proceeds
• What are five factors affecting the rate of a chemical reaction?

  Concentration, pressure, surface area, temperature, catalysts
• What is the collision theory?

  Reactions occur when particles collide with sufficient energy
• How does increasing temperature affect the rate of reaction?

  Higher temperature increases kinetic energy and collision frequency
• What is the relationship between temperature and reaction rate?

  Not directly proportional; varies with conditions
• How does increasing concentration affect the rate of reaction?

  More reactants lead to more frequent collisions
• How does increasing pressure affect the rate of reaction for gases?

  Increases frequency of collisions, similar to concentration
• What is the relationship between volume and pressure in reactions?

  Increasing volume retards the reaction
• How does increasing surface area affect the rate of reaction?

  Smaller pieces increase surface area and collision frequency
• What is a catalyst and how does it affect reactions?

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

  It provides a pathway with lower activation energy
• What is an enzyme?

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

  Products can react to form original reactants
• When is dynamic equilibrium reached?

  When forward and reverse reactions occur at the same rate
• What is Le Chatelier’s Principle?

  System responds to counteract changes and restore equilibrium
• How does changing the concentration of reactants or products affect equilibrium?

  Concentrations change until equilibrium is re-established
• How does increasing temperature affect the position of equilibrium?

  Increases products for endothermic reactions, decreases for exothermic
• How does changing pressure affect the position of equilibrium?

  Shifts towards side with fewer gas molecules
• How does a catalyst affect the position of equilibrium?

  No effect; speeds up both forward and backward reactions