1. General, Organic, and Biological Chemistry
Chemical Reactions II – Oxidation Reduction, Chemical Kinetics and Chemical Equilibrium
General, Organic, and Biological Chemistry

2. Oxidation-Reduction Reactions
An oxidation–reduction reaction
Can fall in any one of the 4 basic type of reaction categories
Involves transfer of electrons from one reactant to the other
provides us with energy from food
provides electrical energy in batteries
occurs when iron rusts
4Fe(s) + 3O2(g) Fe2O3(s)
General, Organic, and Biological Chemistry

3. Transfer of Electrons in Oxidation-Reduction Reactions
Zn(s) + CuSO4(aq)  ZnSO4 (aq) + Cu(s)
An oxidation–reduction reaction
transfers electrons from one reactant to another
Oxidation Is a Loss of electrons (OIL)
Zn(s) Zn2+(aq) + 2e
Reduction Is a Gain of electrons (RIG)
Cu2+(aq) + 2e Cu(s)

4. Oxidation and Reduction - electron transfer
Reactant A transfers an Electron to Reactant B.
Reactant A becomes oxidized.
Reactant B becomes reduced

5. Oxidized or Reduced?

6. Oxidation–Reduction in Biological Systems
In biological systems, oxidation may involve
the loss of H
the gain of O
In biological systems, reduction may involve
the gain of H
the loss of O

7. Summary of Oxidation and Reduction

8. Chapter 6 Chemical Reactions and Quantities
General, Organic, and Biological Chemistry

9. Reaction Conditions
Reaction conditions for a chemical reaction require
collisions between reacting molecules
collisions with sufficient energy to break the bonds in the reactants
the breaking of bonds between atoms of the reactants
the forming of new bonds to give products
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

10. Collision Theory of Reactions
A chemical reaction occurs when
collisions between molecules have sufficient energy to break the bonds in the reactants
molecules collide with the proper orientation
bonds between atoms of the reactants (N2 and O2) are broken and new bonds (NO) form
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

11. Chemical Reactions In the reaction H2(g) + I2(g) 2HI(g),
the reactants H2 and I2 collide
the bonds of H2 and I2 break
the bonds for HI form
H2 + I collision bonds break HI
new bonds form
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

12. Activation Energy Activation energy
is the minimum energy required upon collision for a reaction to take place
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

13. Heat of Reaction The heat of reaction
is the amount of heat absorbed or released during a reaction
is the difference in the energy of the reactants and the products
Heat content of a system is related to the enthalpy = H
Heat of reaction is the change in enthalpy = ΔH
ΔH = ΔHproducts − ΔHreactants
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

14. Exothermic Reactions In an exothermic reaction,
the energy of the products is less than the energy of the reactants
heat of reaction is released
heat is a product
C(s) + O2(g) CO2(g) kJ
ΔH = –394 kJ/mole (heat released)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

15. Endothermic Reactions
In an endothermic reaction,
heat is absorbed
the energy of the products is greater than the energy of the reactants
heat is a reactant
N2(g) + O2(g) kJ NO(g)
ΔH = 180 kJ (heat added)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

16. Summary Reaction Energy Heat Sign of Type Change in Reaction ΔH
Endothermic Heat absorbed Reactant side
Exothermic Heat released Product side –
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

17. Activation Energy – Affects reaction rates (kinetics)
Reaction rate can be increased by
increasing concentration of reactants
decreasing activation energy
The activation energy
is the minimum energy needed for a reaction to take place upon proper collision of reactants
Lower activation energy, speed up reaction
Activation energy lowered by
increasing T
a catalyst
General, Organic, and Biological Chemistry

18. Reversible Reactions
In a reversible reaction, there are both forward and
reverse reactions.
Suppose SO2 and O2 are present initially. As they collide, the forward reaction begins.
2SO2(g) + O2(g) SO3(g)
As SO3 molecules form, they also collide in the reverse reaction that forms reactants. This reversible reaction is written with a double arrow.
forward
reverse
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

19. General, Organic, and Biological Chemistry
Chemical Equilibrium
the rate of the forward reaction = equal to the rate of the reverse reaction
there is no further change in the amounts of reactant and product
General, Organic, and Biological Chemistry

20. Equilibrium At equilibrium, the forward reaction of N2 and O2 forms NO
the reverse reaction of 2NO forms N2 and O2
the amounts of N2, O2, and NO remain constant
N2(g) + O2(g) NO(g)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

21. Chemical Equilibrium
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

22. Equilibrium Constants
For the reaction
aA bB
The equilibrium constant expression, Kc, gives the concentrations of the reactants and products at equilibrium:
Kc = [B]b = [Products]
[A]a [Reactants]
The square brackets indicate the moles/liter of each substance.
The coefficients b and a are written as superscripts that raise the moles/liter to a specific power.
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

23. Writing a Kc Expression
Write the Kc expression for the following:
STEP 1 Write the balanced equilibrium equation:
2CO(g) + O2(g) CO2(g)
STEP 2 Write the product concentrations in the numerator and the reactant concentration in the denominator:
Kc = [CO2] [products]
[CO][O2] [reactants]
STEP 3 Write the coefficients as superscripts:
Kc = [CO2]2
[CO]2 [O2]
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

24. Learning Check The Kc expression for the following reaction is:
2KClO3(s) KCl(s) + 3O2(g)
1) [KCl][O2] 2) [KCl]2[O2]3
[KClO3] [KClO3]2
3) [KCl]2[O2]3 4) [O2]3
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

25. Le Châtelier’s Principle
Le Châtelier’s principle states that
any change in equilibrium conditions upsets the equilibrium of the system
a system at equilibrium under stress will shift to relieve the stress
there will be a change in the rate of the forward or reverse reaction to return the system to equilibrium
NOTE: Catalysts only increase reaction rate, NOT equilibrium
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

26. Effect of Adding Reactant or Product
Consider the following reaction at equilibrium.
H2(g) + F2(g) HF(g)
If more reactant (H2 or F2) is added, there is an increase in the number of collisions.
The rate of the forward reaction increases and forms more HF product until new equilibrium concentrations equal Kc again.
The effect of adding a reactant shifts the equilibrium toward the products (shift to right).
The opposite happens if more product was added (shift to the left).
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

27. Adding Reactant or Product
The equilibrium shifts toward
products when H2(g) or F2(g) is added
reactants when HF(g) is added
H2(g) + F2(g) HF(g)
Add H2 or F2
Add HF
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

28. Exothermic Reactions In an exothermic reaction,
the energy of the products is less than the energy of the reactants
heat of reaction is released
heat is a product
C(s) + O2(g) CO2(g) kJ
ΔH = –394 kJ/mole (heat released)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

29. Endothermic Reactions
In an endothermic reaction,
heat is absorbed
the energy of the products is greater than the energy of the reactants
heat is a reactant
N2(g) + O2(g) kJ NO(g)
ΔH = 180 kJ (heat added)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

30. Heat, Endothermic and Exothermic Reactions
For an endothermic reaction at equilibrium,
decrease in temp (T) shifts toward the reactants
increase in temp shifts toward products.
CaCO3(s) kcal CaO(s) + CO2(g)
For an exothermic reaction at equilibrium,
increase in temp (T) shifts toward the reactants
decrease in temp shifts toward products.
N2(g) + 3H2(g) NH3(g) kcal
Decrease T
Increase T
Decrease T
Increase T
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

31. Learning Check
Predict any shift in equilibrium for each of the following
changes on the reaction
NH4HS(s) H2S(g) + NH3(g)
1) to products 2) to reactants 3) no change
A. H2S(g) is added.
B. NH4HS(s) is added.
C. NH3(g) is removed.
D. A catalyst is added.
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

32. Learning Check
Indicate if each change on a reaction at equilibrium shifts
2NO2(g) + heat NO(g) + O2(g)
1) towards products 2) towards reactants
3) no change
A. adding NO(g)
B. adding NO2(g)
C. raising the temperature
D. removing O2(g)
E. increasing the volume
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

33. Kinetic Theory and Properties of Gases
A gas consists of small particles that
move rapidly in straight lines
have essentially no attractive (or repulsive) forces
are very far apart
have very small volumes compared to the volumes of the containers they occupy
have kinetic energies that increase with an increase in temperature
Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and moles (n).
General, Organic, and Biological Chemistry

34. Ideal Gas Law
The relationship between the four properties (P, V, n, and T) described by the ideal gas law.
PV = nRT
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

35. General, Organic, and Biological Chemistry
Learning Check
Dinitrogen oxide (N2O), laughing gas, is used by dentists as an anesthetic. If a 20.0 L tank of laughing gas contains 2.86 moles of N2O at 23 °C, what is the pressure (mmHg) in the tank?
General, Organic, and Biological Chemistry