Chemical Reactions & Equations Kinetics Rate of Reaction Dr. Ron Rusay TED Intro: https://www.youtube.com/watch?v=OttRV5ykP7A

Kinetics Molecules must collide in order to react Kinetics Molecules must collide in order to react. How does this relate to the speed of a chemical reaction? Rate of Reaction For the Chemical Reaction: Mg(s) + 2 H2O(l) Mg(OH)2 (aq) + H2 (g) a A + b B  c C + d D 1 [Change in concentration of Mg(OH)2 (aq) ] = 1 Change in time (seconds)

Molecules must collide in order to react. Activation Energy, (Ea) & Temperature: molecules must collide with enough energy to react. Raising the temperature increases the K.E. of the molecules, the number of collisions and the energy of the collisions. Generally, raising the temperature 10oC doubles the rate.

QUESTION Which line in the Energy Diagram corresponds to the activation energy for the forward reaction? X Y Z W

QUESTION Which line in the Energy Diagram corresponds to the activation energy for the reverse reaction? X Y Z W

Molecules must collide in order to react. Ea-2.MOV Ea-3.MOV http://chemconnections.org/general/movies/Ea-1.MOV

Molecules must collide in order to react. Concentration: The higher the concentration, the higher number of collisions. Rate = k (collision frequency) = k (concentration) http://chemconnections.org/general/movies/html-swf/reactionrate_conc.htm

Molecules must collide in order to react. Physical state: molecules must physically mix in order to collide. The physical state (solid, liquid, gas) will affect frequency of collisions, as well as the physical size of droplets (liquid) or particles in the case of solids (heterogeneous vs. homogeneous).

Catalysts: change the reaction’s pathway, lowering the Energy of Activation, and increase the reaction rate. http://chemconnections.org/general/movies/html-swf/homogeneouscatalysis.htm

Enzymes Catalytic Power Enzymes can accelerate biological reactions as much as 1016 times over uncatalyzed rates, i.e., 10,000,000 billion times! Urease: (Found in bacteria, yeast & higher plants) Breaks down urea into ammonia, CO2 and releases energy. Catalyzed rate: 3 x 104/sec Uncatalyzed rate: 3 x 10-10/sec Relative difference is 1 x 1014 (100,000 billion times)

Enzymes Catalytic Power Enzymes lower the Energy of Activation.

Human Circadian Rhythm Oscillating Reactions & Homeostasis At what time of day will most people produce urine at the fastest rate? At what time of day will you most likely have an allergic reaction? Begin Here (1 cycle 24 hour Clock) ~6:00 PM ~11:00 PM http://www.sciencedirect.com/science/article/pii/0021870765900869

Factors that Effect Reaction Rates Molecules must collide in order to react. 1) Concentration: The higher the concentration, the higher number of collisions. Rate = k (collision frequency) = k (concentration) k = rate constant 2) Physical state: Molecules must physically mix to come in contact and collide. 3) Energy/Temperature: (Activation Energy, Ea) Molecules must collide effectively with enough energy to react. Raising the temperature increases the number of effective collisions and the energy of the collisions. 4) Catalysts: Lower the Energy of Activation and speed up the reaction.

QUESTION The electrolysis of water is the reverse of the synthesis of water. The synthesis reaction is exothermic. Which equation best represents the overall reaction, which includes thermochemistry, that takes place when water is electrolyzed? A) H2O(l) → H2O(g) + energy B) H2O(g) → H2O(l) + energy C) 2 H2O(l) + energy → 2 H2(g) + O2(g) D) 2 H2(g) + O2(g) +energy → 2 H2O(l) E) 2 H2O(l) → 2 H2(g) + O2(g) + energy Correct Answer: C Question Number: 5