Kinetics

• Reaction rate is defied as the change in concentration (or amount) of a reactant or product over time
• Rate of reaction = amount of reactant used or product formed / time
• A reaction wont take place unless:

  • they collide in the right direction
  • have the minimum amount of kinetic energy
• The minimum amount of kinetic energy that particles need to react is called activation energy
• Fill in the graph

  A) Energy

  B) Number of molecules

  C) Most probable energy

  D) Average energy

  E) activation energy

  
• The area under the maxwell Boltzmann curve is equal to the total number of molecules
• The curve starts at (0,0) because no molecules have no energy
• Increasing temperature makes the reaction faster
• When the temperature is warmer the maxwell Boltzmann graph is shifted to the right as more particles have activation energy. This also causes the particles to collide more often therefore increasing rate of reaction
• Increasing concentration increases the rate of reaction
• Increasing concentration:

  The particles will be closer together and they will collide more often and more frequently and therefore they will have more of a chance of colliding and increasing rate of reaction
• Increasing pressure increases rate of reaction
• Increasing pressure:

  particles are closer together and collide more frequently so there is a higher chance of successful collisions which increase rate of reaction
• Catalyst increase rate of reaction
• A catalyst is a substance that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction
• On an energy profile when a catalyst is added the activation energy decreases
• On a Maxwell Boltzmann curve when a catalyst is added the activation energy line is moved to the left
• Ways to measure rate of reaction:

  • Timing how long it take precipitate to form
  • Measuring a decrease in mass
  • Measuring the volume of gas given off
• What does the collision theory state about chemical reactions?

  Particles must collide correctly and with energy
• What is an ineffective collision?

  Particles collide incorrectly or lack energy
• What distinguishes an effective collision?

  Correct orientation and sufficient energy present
• What is collision frequency?

  Number of collisions per unit time
• How does an increase in collision frequency affect reaction rate?

  It increases the number of effective collisions
• What is activation energy (E)?

  Minimum energy needed for a reaction
• How do exothermic and endothermic reactions differ in terms of energy?

  Exothermic reactants are higher in energy
• Why is the activation energy larger in endothermic reactions?

  Reactants are lower in energy than products
• What must reactant particles do for a collision to be effective?

  Collide in correct orientation and energy
• What is a catalyst?

  Substance that increases reaction rate without participating
• How does a catalyst affect activation energy?

  Provides an alternative pathway with lower energy
• What happens to the rate of reaction with a catalyst?

  It increases compared to the uncatalyzed reaction
• What is the effect of temperature on reaction rates?

  Higher temperature increases reaction rates
• How does temperature affect particle movement?

  Particles gain kinetic energy and move faster
• What happens to the Maxwell-Boltzmann distribution curve with increased temperature?

  It flattens and shifts to the right
• Why does an increase in temperature lead to more effective collisions?

  Particles have more kinetic energy and collide more
• What is the relationship between concentration and reaction rate?

  Higher concentration increases reaction rate
• How does pressure affect reaction rates in gases?

  Increased pressure increases collision frequency
• What is the effect of increasing pressure on gas reactions?

  It increases the rate of reaction
• What are the two types of catalysts?

  Homogeneous and heterogeneous catalysts
• What distinguishes homogeneous catalysts from heterogeneous catalysts?

  Same phase as reactants vs. different phase
• How do catalysts affect the proportion of molecules with activation energy?

  Increases the proportion of molecules with energy