Kinetics Lesson 4 PE Diagrams

Potential Energy Diagrams   Kinetic Energy (kJ) Heat energy due to the motion of particles. Simulation Potential Energy or Enthalpy (H). ΔH means change in enthalpy It is also called the heat of the reaction because it tells you how much heat or KE was produced or consumed by the reaction. Bond Energy (kJ)

PE + KE = Total Energy is constant   Conservation of Energy PE KE ΔH Reaction Type Decreases Increases -ve exothermic Increases Decreases +ve endothermic When PE (bond energy) decreases it is converted into KE which increases. Remember that KE is heat energy, so it gets hotter and it is exothermic.

Potential Energy Diagrams Exothermic Show the change in potential energy or enthalpy during a successful collision. Standard Notation:   H2 + I2 → 2HI + 170 kJ ΔH Notation: H2 + I2 → 2HI ΔH = -170 kJ Both notations indicate an exothermic reaction. The first indicates that 170 KJ of KE are produced, while the second shows that the PE decreases by 170 KJ. On the right Or negative

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 KJ 1. An H2 and I2 approach each other

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 1. Reactants H2 and I2 approach each other Reactants PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 2. They collide and become an Activated Complex PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 2. They collide and become an Activated Complex Unstable Reaction Intermediate High PE Low KE Bonds Break & Form Reactant bonds break Activated complex bonds form PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 3. New bonds form and products separate PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 3. New bonds form and products separate activated complex bonds break product bonds form PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 3. New bonds form and products separate Activated Complex Reactants Products PE Reaction Path

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 3. New bonds form and products separate PE Reaction Path Ea(for) Ea(rev)

Lets Explore the Potential Energy Changes during a Single Collision H2 + I2 → 2HI + 170 kJ 3. New bonds form and products separate PE Reaction Path Ea Ea(rev) ΔH = -ve

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ H2 + I2 → 2HI ΔH = -170 kJ     600 400 200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ H2 + I2 → 2HI ΔH = -170 kJ     600   reactants 400 200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ H2 + I2 → 2HI ΔH = -170 kJ     600   reactants Ea 400 200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ H2 + I2 → 2HI ΔH = -170 kJ     600   reactants Ea 400 ΔH 200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ. H2 + I2 → 2HI ΔH = -170 kJ       600   reactants Ea 400 ΔH 200   PE (KJ) Reaction Path

Potential Energy Diagrams Endothermic   Standard Notation: I2 + Cl2 + 100 kJ → 2ICl ΔH Notation: I2 + Cl2 → 2ICl ΔH = + 100 kJ Both notations indicate an endothermic reaction. The first indicates that 100 kJ of KE are consumed, while the second shows that the PE increases by 100 kJ. on left or positive

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path  

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path  

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path  

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path  

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path   ΔH = + 100 KJ

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path   ΔH = + 100 KJ

Draw the PE diagram if the enthalpy of the reactants is 400 KJ and the energy of the activated complex is 600 KJ.   I2 + Cl2 + 100 KJ → 2ICl    PE 600 400 200 Reaction Path   Ea ΔH = + 100 KJ

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   400   200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   400   200   PE (KJ) Reaction Path

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   400   200   PE (KJ) Reaction Path Ea (rev) = 400 kJ

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   400   200   PE (KJ) Reaction Path Ea (rev) = 400 kJ

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   Ea (for) = 200 kJ   400   200   PE (KJ) Reaction Path Ea (rev) = 400 kJ

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   Ea (for) = 200 kJ   400   200   PE (KJ) Reaction Path Ea (rev) = 400 kJ

Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ     600   Ea (for) = 200 kJ   400   200   PE (KJ) Reaction Path Ea (rev) = 400 kJ ΔH = -200 kJ

Exothermic Reaction

Exothermic Reaction Uncatalyzed reaction

Exothermic Reaction Uncatalyzed reaction Catalyzed reaction

Exothermic Reaction Reactants Products

Exothermic Reaction Reactants Products stronger bonds

Exothermic Reaction Downhill in PE KE is produced

Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat)

Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat) Ea(for)(cat)

Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat) Ea(for)(cat) H

Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat) Ea(for)(cat) Ea(rev)(cat) H

Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat) Ea(rev)(uncat) Ea(for)(cat) Ea(rev)(cat) H

PE(kJ) 500 400 300 200 100 reaction path H forward = H reverse = Ea forward uncat = Ea reverse uncat = Ea forward cat =

PE(kJ) 500 400 300 200 100 reaction path H forward = -300 kJ H reverse = Ea forward uncat = Ea reverse uncat = Ea forward catalyzed =

PE(kJ) 500 400 300 200 100 reaction path H forward = -300 kJ H reverse = +300 kJ Ea forward uncat = Ea reverse uncat = Ea forward catalyzed =

PE(kJ) 500 400 300 200 100 reaction path H forward = -300 kJ H reverse = +300 kJ Ea forward uncat = 100 kJ Ea reverse uncat = Ea forward catalyzed =

PE(kJ) 500 400 300 200 100 reaction path H forward = -300 kJ H reverse = +300 kJ Ea forward uncat = 100 kJ Ea reverse uncat = 400 kJ Ea forward catalyzed =

PE(kJ) 500 400 300 200 100 reaction path H forward = -300 kJ H reverse = +300 kJ Ea forward uncat = 100 kJ Ea reverse uncat = 400 kJ Ea forward catalyzed = 50 kJ

PE(kJ) reaction path Slow rate due to high Ea

PE(kJ) reaction path The only way to change the PE diagram is to add a catalyst.

PE(kJ) reaction path The only way to change the PE diagram is to add a catalyst. More low energy collisions are successful!

PE(kJ) reaction path Slow rate due to high Ea

PE(kJ) 500 400 300 200 100 reaction path Increasing the temperature does not change the diagram. It gives more collisions the required Ea and more are successful. Increasing the concentration, pressure, and surface area does not change the diagram.