1. Unit 1 – Reaction Kinetics Chemistry 12
1.4 – Experimental Measurement of Reaction Rates

2. [Reactant] is initially high As reaction occurs, [reactant] decreases
Therefore, reaction rate is fastest
As reaction occurs,
[reactant] decreases
causing a slower
reaction rate
Exact rate is given by the slope of the line tangent to the curve at that time

3. Do p.11 #18-19

4. Unit 1 – Reaction Kinetics Chemistry 12
1.5 – Reaction Rates and Collision Theory

5. What causes reactions to occur?
Collision theory (or Kinetic Molecular theory) states that molecules act as small, hard spheres which bounce off each other and transfer energy among themselves during their collisions … This means all reactions require collisions!

6. What does this mean? Effect of Concentration
Higher concentration = More molecules able to collide
Therefore, reaction rate INCREASES

7. What does this mean? Effect of Temperature
Higher temperature = higher Kinetic Energy (KE)
Therefore, more movement, greater speed, and reaction rate INCREASES
Kinetic Energy – The energy which a system possesses because of movement within the system
*Note: There are other reasons for increase in reaction rate…. later

8. Do p. 12 #20-22

9. Chemistry 12 Unit 1 – Reaction Kinetics
1.6 – Enthalpy Changes in Chemical Reactions

10. Bond Energies
Potential Energy – Energy existing as a result of an object’s position in space, as well as the sum of all the attractive and repulsive forces existing among the particles which make up the object.
PE is directly related to the energy of the electrons in the chemical bonds, as well as the number and types of atoms in the molecules

11. Potential Energy
Negatively charged electrons hold positively charged nuclei together  Form chemical bond
Electrons repel each other
Nuclei repel each other
*Therefore, the push and pull of all these
forces together result in potential energy

12. a) Bond Energies
Kinetic Energy - The energy which a system possesses because of movement within the system
By moving the entire system or moving the molecules in the system (or individual atoms within the molecules)

13. How are these used together?
Bond Energy – The amount of energy required to break a bond between two atoms To break a bond: Energy added must equal bond energy Cl2(g) kJ  2 Cl(g)

14. To form a bond: Bond energy must equal released energy 2Cl(g)  Cl2(g) + 243 kJ

15. High initial PE, then it releases energy to form a bond
High initial PE, then it releases energy to form a bond. This allows it to be at a more stable level of energy
H + H H2
Potential energy
Reaction Proceeds
Potential Energy Diagram
Remember: Atoms are more stable with a full octet. So, bonds completes this octet

16. Low initial PE, then energy is added to break a bond
Low initial PE, then energy is added to break a bond. This allows it to be at a more stable level of energy
H + H H2
Potential energy
Reaction Proceeds
Potential Energy Diagram

17. b) Reaction Heats
Enthalpy (H) – The total kinetic and potential energy which exists in a system when at constant pressure ΔH = HPROD – HREACT ΔH = The change in enthalpy during the course of the reaction HPROD = Combined enthalpies of all products HREACT = Combined enthalpies of all Reactants

18. HREACT HPROD ΔH = HPROD – HREACT Enthalpy Diagram Enthalpy (H)
Reaction Proceeds
Enthalpy Diagram ΔH
We only need Change in enthalpy value. Will not use H prod or Hreact

19. c) The sign of ΔH
Endothermic  Products have MORE energy than reactants HPROD > HREACT Therefore, ΔH = HPROD – HREACT ΔH > 0

20. 2N2O 2N2 + O2 Endothermic Reaction 2 N2 + O2 + 164kJ  2 N2O
2 N2 + O2  2 N2O ; ΔH = +164kJ
Heat included in REACTANTS of the equation
Enthalpy is POSITIVE
2N2O
2N2 + O2
Enthalpy (H)
Reaction Proceeds
Enthalpy Diagram
ΔH = +164kJ
Note: Arrow up means the reactants GAIN energy to become products

21. ENdo = ENter  Heat ENters the system
Endothermic Reaction
ENdo = ENter  Heat ENters the system
Heat (Energy) is being absorbed into the system
*System = Reactants in reaction
*Surroundings = Container reaction takes place in or surroundings around reaction
Surroundings
System
System becomes warmer
 Surroundings become cooler

22. Exothermic Reaction
Exothermic  Products have LESS energy than reactants
HPROD < HREACT
Therefore, ΔH = HPROD – HREACT
ΔH < 0

23. Exothermic Reaction H2 + Cl2 2HCl H2 + Cl2  2 HCl + 184 kJ
Heat included in PRODUCTS of the equation
H2 + Cl2  2 HCl kJ
H2 + Cl2  2 HCl ; ΔH = -184kJ
Enthalpy is NEGATIVE
2HCl
H2 + Cl2
Enthalpy (H)
Reaction Proceeds
Enthalpy Diagram
ΔH = -184 kJ
Note: Arrow down means the reactants LOSE energy to become products

24. EXo = EXit  Heat EXits the system
Exothermic Reaction
EXo = EXit  Heat EXits the system
Heat (Energy) is being released into the surroundings
*System = Reactants in reaction
*Surroundings = Container reaction takes place in or surroundings around reaction
Surroundings
System
System becomes cooler
 Surroundings become warmer

25. Homework Questions
1.4 – p.11 # – p.12 # – p #23-28