Chemistry Final Exam Revision

• A rate is a measure of change within a specific amount of time.
• Speed, acceleration, and growth rate are all examples of rates.
• The reaction rate is the rate at which reactants become products.
• As the amount of reactants decreases, the amount of products increases.
• The rate of change is faster at the beginning of the reaction.
• Why do you think a reaction might start off and then slow down as time passes?


  The reactant concentrations are usually high at first, so there are many collisions between reactant particles, and the reaction rate is fast. Later, reactant concentrations drop, and there are fewer collisions. Fewer collisions cause the reaction rate to slow.
• Based on the collision theory, why would increasing the concentration increase the reaction rate?

  There would be more particles, increasing the number of collisions, thus increasing the number of collisions that lead to a reaction.
• Based on the Collision Theory, why would increasing the temperature increase the reaction rate?


  Particles will have more kinetic energy so they will collide more often and with more force.
• Based on Collision Theory, why would increasing the surface area (by breaking a reactant up into smaller pieces) increase the reaction rate?


  Increased surface area increases the number of particles available for collisions. WIth more surface area exposed, there is more area available for collisions.
• The rate of a reaction depends in part on the concentration of the reactants. If you had a reaction with only one reactant and one product, a simple equation for the reaction could be :

  A --> B
• We said that the rate of a reaction is the rate of change in concentration of the reactants or products.

  Rate = Change in concentration of A ÷ change in time
• The rate of disappearance of A is proportional to the concentration of A. This means the more reactant A there is, the faster A disappears and the less there is, the slower it disappears. We can represent this using an equation called a rate law.

  Rate = k * [A]
• Reaction Rate Formula:

  Change in concentration of reactant or product/change in time * 1/Coeffecient of reactant or product