1. Ch. 4 Chemical Reactions
Homework: 4.17, 4.18, 4.30, 4.33, 4.43, 4.45, 4.49, 4.55, 4.60, 4.62, 4.63, 4.73, 4.78, 4.100

2. Chemical Reactions
In a chemical change, also known as a chemical reaction, one or more of the starting materials, called reactants, are converted into one or more products
There are 3 aspects of a chemical reaction:
Mass relationship
Types of Reactions
Heat gains and loses

3. Background for Mass relationships
Formula Weight- the sum of the atomic weights in amu of all atoms in the compound’s formula
Formula weight applies to ionic compounds, and covalently bonded molecules
Molecular Weight- means the same thing but only applies to molecules

4. The mole
Mole- the amount of substance that contains as many atoms, molecules, or ions as there are atoms in 12 grams of carbon 12.
A mole always contains the same number of formula units
That number, known as Avogadro’s Number, is 6.02 x 1023

5. Molar Mass
Molar Mass- the mass of one mole of any substance is the formula weight expressed in grams.
To convert between grams and moles, we use the Molar Mass as the conversion factor:

6. Writing Chemical Equations
We use the formulas for the reactants and products
We use an arrow to show the direction of the reaction
We also designate the state of all reactants and products!!
(s)=solid, (l)=liquid, (g)=gas, (aq)=aqueous
(aqueous means the substance is dissolved in water)

7. Example:
Chemical Equations must be balanced!!!!
This means there must be the same number of atoms on the left as on the right
To balance equations, we put coefficients in front of the formulas until we have the same number of each type of atom on both sides.

8. Guidelines for balancing Eq.
Begin with atoms that appear in only one compound on the left and right
If an atom occurs as a free element, balance this element last
You can only change coefficients, NOT FORMULAS!!!!!
A balanced equation is always written with the lowest possible set of coefficients.

9. Examples

10. Stoichiometry
Stoichiometry- the study of mass relationships in chemical reactions
The balanced equation gives us the molar ratios of the reactants and products.
We can use this information to calculate the mass of starting material needed to produce a certain amount of product or vice versa.

11. Basic Process=
Example=

12. Limiting Reagent
The limiting reagent is the reactant that will be used up first.
Example-

13. Percent Yield
Actual Yield- the mass of a product formed in a chemical reaction that is physical carried out
Theoretical Yield- the mass of product that SHOULD form according to the stoichiometry of the balanced equation
Percent Yield- The actual yield divided by the theoretical yield time 100%

14. Combination Example
A student combusted 6.0 grams of C3H8 in the presence of 30 grams of O grams of water was captured. What was the percent yield for the reaction?

15. Ionic Reaction in Aqueous Solutions
When positive and negative ions are placed in water, the ions are separated
This is called dissociation
Ions in water react with each other in solution only when one of the following can happen:

16. Types of Reactions Two ions form a solid that is insoluble in water
2 ions form a gas that escapes from the reaction mixture as bubbles
An acid neutralizes a base
One of the ions can oxidize the other

17. Example
Say we mix a solution of NaCl with a solution of AgNO3

18. Ion Solubility Rules
All compounds containing Na+, K+, or NH4+ are soluble in water
All nitrates(NO3-) and acetates(CH3COO-) are soluble in water
Most Chlorides(Cl-), and Sulfates(SO42-) are soluble in water. EXCEPTIONS: AgCl, BaSO4, PbSO4
Most Carbonates(CO32-), phosphates(PO43-), sulfides(S2-), and hydroxides(OH-) are insoluble in water. EXCEPTIONS: LiOH, NaOH, KOH, NH4OH

19. Example
Will a reaction occur if a solution of Na2CO3 and a solution of LiCl are mixed together?

20. Oxidation Reduction Reactions
Oxidation- is the loss of electrons
Reduction- is the gain of electrons
And Oxidation/Reduction reaction, aka Redox reaction, involves the transfer of electrons from one species to another.

21. Example

22. These reactions are not independent of one another
Something can’t gain electrons from nowhere!!!

23. Organic Definitions
In organic Chemistry, it is very hard to figure out what lost electrons and what gained them, so we use different definitions:
Oxidation- a reaction in which there is an increase in the number of bonds to Oxygen and/or a decrease in the number of bonds to Hydrogen.
Reduction- a reaction in which there is an increase in the number of bonds to Hydrogen and/or a decrease in the number of bonds to Oxygen.

24. Categories of Redox Reactions
Combustion
-What ever is burned is oxidized by O2
Respiration
-O2 oxidizes carbon containing molecules to produce CO2 and water, much like a combustion but much slower and lower temperature
Rusting
-Iron is oxidized to Iron Oxide

25. 4) Bleaching
-Most bleaching involves oxidation
5) Batteries
- The reaction in the battery is a redox reaction.

26. Heats of Reactions
Heat of Reaction- the heat given off or absorbed by a chemical reaction
If a reaction gives off heat, it is exothermic
If a reaction absorbs heat, it is endothermic
Heat given off in a combustion reaction is called heat of combustion.