Kinetics Lesson 4 PE Diagrams

KineticsLesson 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)

http://www.falstad.com/gas/

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 CollisionH2 + I2 → 2HI + 170 KJ

1. An H2 and I2 approach each other

Lets Explore the Potential Energy Changes during a Single CollisionH2 + I2 → 2HI + 170 kJ

1. An H2 and I2 approach each other

Reactants


1. Reactants H2 and I2 approach each other

Reactants

PE

Reaction Path


2. They collide and become an Activated Complex

PE

Reaction Path


2. They collide and become an Activated ComplexUnstableReaction IntermediateHigh PE Low KEBonds Break & Form

Bonds break

PE

Reaction Path


3. New bonds form and products separate

Products

PE

Reaction Path



Products

bonds form

PE

Reaction Path



Products

PE

Reaction Path

Ea(for)



Products

PE

Reaction Path

Ea(rev)



Products

PE

Reaction Path

Ea

ΔH = -ve

Ea(rev)

Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJH2 + I2 → 2HI ΔH = -170 kJ

600

400

200

0

PE (KJ)

Reaction Path


600 reactants

400

200

0

PE (KJ)

Reaction Path


600 reactants Ea

400

200

0

PE (KJ)

Reaction Path


600 reactants Ea

400 ΔH

200

0

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

0

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 leftor 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

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

Ea

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 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 reactionCatalyzed reaction

Exothermic Reaction

Reactants

Products

Exothermic Reaction

Reactants

Productsstronger bonds

Exothermic Reaction

Downhill in PEKE is produced

Exothermic Reaction


Ea(for)(uncat)

Exothermic Reaction


Ea(for)(cat)

Ea(for)(uncat)

Exothermic Reaction


H

Ea(for)(cat)

Ea(for)(uncat)

Exothermic Reaction


H

Ea(rev)(cat)Ea(for)(cat)

Ea(for)(uncat)

Exothermic Reaction


H

Ea(rev)(cat)Ea(for)(cat)

Ea(for)(uncat) Ea(rev)(uncat)

PE(kJ)500

400

300

200

100

0reaction path

H forward =H reverse =Ea forward uncat =Ea reverse uncat =Ea forward cat =

PE(kJ)500

400

300

200

100

0reaction path

H forward = -300 kJH reverse =Ea forward uncat =Ea reverse uncat =Ea forward catalyzed =

PE(kJ)500

400

300

200

100

0reaction path

H forward = -300 kJH reverse = +300 kJEa forward uncat =Ea reverse uncat =Ea forward catalyzed =

PE(kJ)500

400

300

200

100

0reaction path

H forward = -300 kJH reverse = +300 kJEa forward uncat = 100 kJEa reverse uncat =Ea forward catalyzed =

PE(kJ)500

400

300

200

100

0reaction path

H forward = -300 kJH reverse = +300 kJEa forward uncat = 100 kJEa reverse uncat = 400 kJEa forward catalyzed =

PE(kJ)500

400

300

200

100

0reaction path

H forward = -300 kJH reverse = +300 kJEa forward uncat = 100 kJEa reverse uncat = 400 kJEa 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

0reaction 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.

Kinetics Lesson 4 PE Diagrams

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