Reaction Rates and Le Chatelier’s Principle

Rate of Reaction The rate of a chemical reaction The number of particles that react in a certain amount of time to form products Describes how rapidly a chemical change takes place They are determined by measuring changes in physical properties Volume, Temperature, Color, Mass, or pH

Five Factors that Effect Reaction Rate 1. Nature of the reactants 2. Temperature 3. Concentration 4. Surface Area 5. Catalysts

Which INCREASE Reaction Rates? Increasing Temperature Increasing Concentration Increasing Surface Area Adding a Catalyst. How are these factors related to Reaction Rates? DIRECTLY

Nature of Reactants Reaction rates are affected by the complexity of the bonds that must be broken and formed in the chemical reaction The state of a reactant can also affect the reaction rate Gases have the fastest and solids the slowest reaction rats Because the frequency at which particles collide and the amount of energy they possess increase with increasing motion.

Continued The faster particles are moving, the more frequent they will collide Collide with greater kinetic energy. Because of this TEMPERATURE and REACTION RATE are directly related

Chemical Equilibrium At equilibrium the forward reaction and the reverse reaction happen at the same time There is no change in the amount of any substance in the reaction Le Chatelier’s principle can be used to predict the effect of a change in conditions on a chemical equilibrium

Le Chatelier’s Principle Summarized If a chemical system at equilibrium experiences a change (also called a stress) in concentration, temperature, volume, or total pressure; the equilibrium will shift in order to minimize that change.

See Saw H2O H OH

Add More Hydrogen H2O OH H H Which way does the see saw have to shift to reach equilibrium again?

Add More Hydrogen H2O OH H H Which way does the see saw have to shift to reach equilibrium again?

Add More Hydrogen H2O OH SHIFT LEFT H H More H2O is produced due to the shift in equilibrium

Synthesis of Ammonia H2 H2 NH3 NH3 N2 H2 N2 (g) + 3H2 (g)  2NH3 (g)

SHIFT will occur to side with the least number of MOLES Increase Pressure SHIFT RIGHT H2 NH3 NH3 H2 H2 N2 SHIFT will occur to side with the least number of MOLES N2 (g) + 3H2 (g)  2NH3 (g)

SHIFT will occur to side with the least number of MOLES Increase Pressure SHIFT RIGHT H2 NH3 NH3 H2 H2 N2 SHIFT will occur to side with the least number of MOLES N2 (g) + 3H2 (g)  2NH3 (g)

Decreasing Volume (Think about how P and V relate with Boyle’s Law) NH3 NH3 N2 H2 N2 (g) + 3H2 (g)  2NH3 (g)

Decrease Volume = Increase Pressure SHIFT RIGHT H2 NH3 NH3 H2 H2 N2 SHIFT will occur to side with the least number of MOLES N2 (g) + 3H2 (g)  2NH3 (g)

Change in Temperature Depends if reaction is Endothermic or Exothermic. Endothermic: Heat on LEFT Exothermic: Heat on RIGHT

Exothermic Increase Temperature… which way will the see saw tip? D A C HEAT D A C B

Which way will the reaction shift? Exothermic A HEAT B C D Which way will the reaction shift?

Reaction will SHIFT LEFT Exothermic A HEAT B C D Reaction will SHIFT LEFT

Exothermic DecreaseTemperature… which way will the see saw tip? D A C HEAT D A C B DecreaseTemperature… which way will the see saw tip?

Which way will the reaction shift? Exothermic HEAT D C B A Which way will the reaction shift?

Reaction will SHIFT Right Exothermic HEAT D C B A Reaction will SHIFT Right

Endothermic Increase Temperature… which way will the see saw tip? D A HEAT D A C B

Which way will the reaction SHIFT? Endothermic Which way will the reaction SHIFT? HEAT D C B A

Reaction will SHIFT Right Endothermic Reaction will SHIFT Right HEAT D C B A

Endothermic Decrease Temperature… which way will the see saw tip? D A HEAT D A C B

Which way will the reaction SHIFT? Endothermic HEAT Which way will the reaction SHIFT? A B C D

Reaction will SHIFT Left Endothermic HEAT Reaction will SHIFT Left A B C D

Reaction Rates Concentration Temperature Pressure Volume