chem rates of reaction

• Rate of reaction


  A measure of how quickly a reactant is used up, or a product is formed
• Collision theory

  • Reactant particles must collide with each other
  • Particles must have enough energy for them to react
• Successful collision


  A collision between reactant particles that has enough energy for a reaction to happen
• Activation energy


  The minimum amount of energy that colliding particles must have for them to react
• Reactions can vary from being almost instantaneous to taking years to complete
• Measuring mass


  The change in mass of a reactant or product can be followed during a reaction
• Measuring volume


  The change in volume of a reactant or product can be followed during a reaction
• Gradient


  On a graph, the gradient is defined as being the change in the 'y' value divided by the change in the 'x' value. It defines how steep a line is.
• The gradient of the line is equal to the rate of reaction: the steeper the line, the greater the rate of reaction
• Fast reactions finish sooner (when the line becomes horizontal) than slow reactions
• Frequency of successful collisions

  The greater the frequency of successful collisions between reactant particles, the greater the reaction rate
• Factors affecting reaction rate

  • Temperature
  • Concentration
  • Pressure
  • Catalysts
• Increased concentration or pressure of a reacting solution or gas

  Reactant particles are closer together, frequency of collisions between reactant particles increases, therefore the rate of reaction increases
• The mean energy of the particles does not change when concentration or pressure is increased
• Increased frequency of collisions

  Increased frequency of successful collisions
• Gradient of a graph of mass or volume of product formed against time

  Equal to the rate of reaction
• The faster reaction at the higher concentration or pressure gives a steeper line and finishes sooner
• Questions should be answered in terms of frequency or rate of successful collisions, rather than the number of successful collisions
• Rate of reaction

  The frequency of successful collisions between reactant particles
• Factors affecting rate of reaction

  • Temperature
  • Concentration
  • Pressure
  • Catalysts
• Increasing surface area to volume ratio

  Increases the rate of reaction
• For a given mass of a solid, large lumps have smaller surface area to volume ratios than smaller lumps or powders
• If a large lump is divided or ground into a powder: its total volume stays the same, the area of exposed surface increases, the surface area to volume ratio increases
• Successful collision

  A collision between reactant particles that has enough energy for a reaction to happen
• Increasing frequency of successful collisions

  Increases the rate of reaction
• Increasing surface area to volume ratio

  Increases the frequency of collisions between reactant particles
• Increasing frequency of collisions between reactant particles

  Increases the rate of reaction
• The mean energy of the particles does not change, but the frequency of successful collisions increases
• Gradient of a graph of product formed against time

  Equal to the rate of reaction
• The faster reaction with the powder gives a steeper line and finishes sooner
• Rate of reaction

  The frequency of successful collisions between reactant particles
• The greater the frequency of successful collisions between reactant particles

  The greater the rate of reaction
• Factors affecting reaction rate

  • Temperature
  • Concentration
  • Pressure
  • Catalysts
• As temperature increases

  Reactant particles move more quickly, the energy of the particles increases, the frequency of successful collisions increases, therefore the rate of reaction increases
• The mean energy of the collisions changes when the temperature changes
• Successful collision

  A collision between reactant particles with enough energy (the activation energy or more than the activation energy) to produce a reaction
• As the rate of reaction increases

  The gradient of the graph of mass or volume of product formed against time increases
• The increase in energy is usually the more important factor in the effect of temperature on the rate of reaction
• Catalyst

  A substance that changes the rate of a chemical reaction without being changed by the reaction itself
• Catalysts

  • Increase the rate of a reaction
  • Do not alter the products of the reaction
  • Are unchanged chemically and in mass at the end of the reaction