1. Bettelheim, Brown, Campbell and Farrell Chapter 4
Chemical Reactions
Bettelheim, Brown, Campbell and Farrell
Chapter 4

2. Chemical Reactions
In a chemical reaction, one or more reactants is converted to one or more products
Formula weight: the sum of the atomic weights in atomic mass units (amu) of all atoms in a compound’s formula
Mass Relationships

3. Compound Mass Molecular Weight: Molecular compounds only
Formula Weight: Molecular or ionic compounds

4. Chemical Equations
The following chemical equation tells us that propane gas and oxygen gas react to form carbon dioxide gas and water vapor
Gives reactants and products and their physical states.
Equation above is NOT balanced
Must be balanced to get mass relationships

5. Balancing Equations
Must have same number of atoms of each kind on both sides of equation. Change coefficients until it is balanced.

6. Balancing Equations
Practice problems: balance these equations

7. Balancing Equations
Practice problems: balance these equations

8. 1 mol HCl = 6.022 x 1023 HCl molecules = 36.5 g HCl
The Mole
Mole (mol)- amount of substance whose mass in grams is numerically equal to its molecular or formula weight
Amount of substance that contains as many atoms, molecules, or ions as are in exactly 12 g of carbon-12
Number of formula units in a mole is known as Avogadro’s number
Equal to x 1023 formula units per mole
1 mol HCl = x 1023 HCl molecules = 36.5 g HCl

9. Moles to Molecules
A tablet of aspirin, C9H8O4, contains mol of aspirin. How many aspirin molecules is this?

10. Moles to Atoms
A tablet of aspirin, C9H8O4, contains mol of aspirin. How many atoms of oxygen does this contain?

11. Molar Mass
Molar mass: the formula weight of a substance expressed in grams
Glucose, C6H12O6
molecular weight: 180 amu
molar mass: 180 g/mol
Urea, (NH2)2CO
molecular weight 60.0 amu
molar mass: 60.0 g/mol

12. Molar Mass
Molar mass can be used to convert from grams to moles, and from moles to grams
calculate the number of moles of water in 36.0 g water

13. Grams to Moles
Calculate the number of moles in 5.63 g of sodium sulfate, Na2SO4
(I mol = 142 g)

14. Grams to Moles
Calculate the number of moles of sodium ions, Na+, in 5.63 g of sodium sulfate, Na2SO4

15. Stoichiometry
Stoichiometry: the study of mass relationships in chemical reactions

17. Stoichiometry
Problem: how many moles of nitrogen, N2, are required to produce 3 moles of ammonia, NH3

18. Stoichiometry
Problem: how many grams of nitrogen, N2, are required to produce 51 g of ammonia, NH3

19. Limiting Reagent
Limiting reagent: the reagent that is used up first in a chemical reaction
Need to determine which reagent is present with the fewest moles
Suppose 12 g of carbon is mixed with 64 g of oxygen and the following reaction takes place
Maximum amount of product can only be equal to the amount produced from the limiting reagent

20. Percent Yield
Theoretical yield: the mass of product that should be formed according to the stoichiometry of the balanced chemical equation
Actual yield: the mass of product formed in a chemical reaction
Percent yield: actual yield divided by theoretical yield times 100

21. Percent Yield
32.0 g of methanol reacts with excess carbon monoxide to produce 58.7 g of acetic acid

22. Percent Yield
32.0 g of methanol reacts with excess carbon monoxide to produce 58.7 g of acetic acid

25. Reactions
When an ionic compound dissolves in water, it dissociates to form aqueous ions
AgNO3(s) → Ag+(aq) + NO3-(aq)
Dissociation Reactions

26. Reactions
When two ionic compounds are dissolved in water, the ions may combine to form new compounds

27. Reactions Between Ions in Solution
Reaction will occur if
a precipitate (solid) forms (see solubility table)
a compound that is insoluble in water
a gas is formed (bubbles or fizzing)
an acid neutralizes a base and water is formed
one of the ions can oxidize another (Redox reaction)

28. Molecular Equation Everything shown as molecules
AgNO3(aq) NaCl(aq) →
AgCl(s) NaNO3(aq)

29. Full Ionic Equation: Shows ions as ions and precipitates as compounds

30. Net Ionic Equation Shows only those species that change in reaction
Ag+(aq) + Cl-(aq) AgCl(s)
Spectator ions do not participate in reaction and do not change (Na+ and NO3-)

31. Solubility Rules Soluble: Compounds with: Exceptions Na+, K+ and NH4+
NO3- and CH3CO2-
Cl-, Br- and I-
Pb2+ , Ag+ and Hg22+ halides are insoluble
Insoluble: Compounds with
CO32- and PO43-
All Na+, K+ and NH4+ are soluble
OH- and S2-
Na+, K+ and Ca2+ and NH4+ sulfides and hydroxides are soluble

32. Oxidation-Reduction Reactions
Oxidation: the loss of electrons or hydrogen
(or gain of oxygen)
Reduction: the gain of electrons or hydrogen
(or loss of oxygen)
Oxidation-reduction (redox) reaction: any reaction in which electrons are transferred from one species to another
Must have BOTH oxidation AND reduction

33. Oxidation-Reduction Reaction
Example: zinc metal is placed in a beaker containing a solution of copper(II) sulfate
some of the zinc metal dissolves
some of the copper ions deposit on the zinc metal
the blue color of Cu2+ ions gradually disappears
zinc metal loses electrons to copper ions
copper ions gain electrons from the zinc

34. Oxidation-Reduction
Summary:

35. Oxidation-Reduction
Although some definitions of oxidation (loss of electrons) and reduction (gain of electrons) are easy to apply to many redox reactions, they are not easy to apply to others
for example, the combustion of methane

36. Heat of Reaction
In almost all chemical reactions, heat is either given off or absorbed
Example: the combustion (oxidation) of carbon liberates 94.0 kcal per mole of carbon oxidized
Exothermic reaction: Heat given off
Endothermic reaction: Heat absorbed