U1 S1 L2 Energy Diagrams MHR: Questions:

Upon completion of this lesson, you will be able to: define activation energy, activated complex, and heat of reaction. draw, label, and interpret potential energy diagrams (or energy profile curves) for exothermic and endothermic reactions. calculate the activation of the forward reaction or the activation energy of the reverse reaction or the heat of reaction given two of these three values for a reversible chemical system.

Temperature and Kinetic Energy Kinetic energy is energy of motion. –KE depends on the mass and velocity (speed) of a particle.

Temperature is an measure of the average kinetic energy. –For example, the air temperature in your room is probably close to 20°C. That means that molecules in the air are moving faster than they do at 0°C, but slower than at 40°C. –Temperature is a measure of average motion of all the particles in the room. Ie: the air in contact with the cold window is moving slower that the air next to the heater!

Potential Energy Potential energy is defined as energy of position or the energy possessed by something due to its position relative to something else. H 2 (g) + O 2(g) → H 2 O (l) + Energy

An energy profile diagram (also known as a potential energy diagram) shows the potential energy changes that occur during a chemical reaction.

Activated complex –The point at which the reactants gain enough energy to form products. –Threshold point (the highest point on the graph) –An unstable group (complex) that instantly breaks apart to form products. Activation Energy (E act ) –The energy barrier to the reaction –The maximum amount of energy needed to start a reaction –The energy required to reach the activated complex E act = E activated complex -E reactants Heat of reaction (∆H) –The heat released (or consumed) when a reaction takes place. Exothermic reaction  heat is released (-∆H) Endothermic reaction  heat is absorbed (+∆H) ∆H = E P - E R

Exothermic Vs: Endothermic

Question The heat of reaction for the formation of water is -286 kJ. Assume that the activation energy for the formation of water from hydrogen and oxygen gas is 112 kJ. Calculate the activation energy for the decomposition of water.

1.What is defined as being proportional to the average kinetic energy of the particles in a sample of matter? A.a Joule B.heat C.potential energy D.Temperature 2.. Which part of the graph represents the activation energy? a)A b)B c)C d)D

3.Which symbol represents the activation energy for the reverse reaction? a)W b) X c) Y d) Z 4.What is the activation energy of the reverse reaction if the heat of reaction is -60 kJ and the activation energy of the forward reaction is 40 kJ? a)20 b)40 c)60 d)100

Textbook Readings page 471: Collision Theory and Temperature page 472: Reactions and Activation Energy pages : Transition State Theory pages : Tracing a Reaction with a Potential Energy Diagram Textbook Practice Items page 476: # 1, 2, 3, and 4 page 484: # 3 and 4 page 487: # 16 pages : # 1, 11, and 14