1. Balancing Equations and Types of Reactions
Chapter 9

2. Word Equations
Iron reacts with oxygen to produce iron (III) oxide, or rust.
Iron + oxygen  iron (III) oxide
Reactants are written to the left of the arrow, and products are written to the right. If there are more than one reactant or product, they are separated by a plus sign.

3. Word Equations
How would I write “hydrogen peroxide reacts to form water and oxygen gas”?
Hydrogen peroxide  water + oxygen

4. Chemical Equations
In a chemical equation, we use the chemical symbols of compounds and elements.
Fe + O2  Fe2O3
This is an example of a skeleton equation, which shows the formulas but does not indicate the relative amounts of reactants and products.

5. States of Matter
You can indicate the physical state of reactants and products by using (s), (l), (g), or (aq) after the chemical formula.
H2O2(aq)  H2O(l) + O2(g)

6. States of Matter
Aqueous solution: contains one or more substances dissolved in water
1. solute: the substance getting dissolved; what you have less of
2. solvent: the substance doing the dissolving; what you have the most of

7. Common Symbols
Catalysts are used in some reactions to speed up the rate. For example, manganese (IV) oxide, MnO2, can be used as a catalyst to speed up the decomposition of water. Catalysts are written above the arrow.
Table 9.1 in your text lists common symbols used in chemical equations.

8. Writing Skeleton Equations
Write skeleton equations for the following reactions.
sulfur burns in oxygen to form sulfur dioxide
heating potassium chlorate in the presence of the catalyst manganese (IV) oxide produces oxygen gas. Potassium chloride is left as a solid.
KClO3(s)  KCl(s) + O2(g)

9. Balancing Chemical Equations
Word equation for bicycle
frame + wheel + handlebar + pedal  bicycle
Which are products and which are reactants?
You might write a chemical formula for the above equation like this…
f + w + h + p  fw2hp2

10. Balancing Equations
Is this a balanced equation? How does this relate to the Law of Conservation of Mass?
In order to balance our equation, we have to put in coefficients. When no coefficient is written, it is assumed to be 1. There must be the same number of atoms of each element.

11. Rules for Balancing Equations
Determine the correct formulas for all the reactants and products.
Write the skeleton equation
Count the atoms of the elements in the reactants
Count the atoms of the elements in the products
Change the coefficients to make the number of atoms of each element equal on both sides of the equation (NEVER CHANGE THE SUBSCRIPT!)
Write the coefficients in their lowest possible ratio
Check your work

12. Balancing Chemical Equations

13. Practice Equations AgNO3 + H2S  Ag2S + HNO3
MnO2 + HCl  MnCl2 + H2O + Cl2
hydrogen + sulfur  hydrogen sulfide
iron (III) chloride + calcium hydroxide  iron (III) hydroxide + calcium chloride

14. Classifying Reactions
Synthesis, Direct Combination, Combination Reactions: two or more substances combine to form a single substance
A + B  AB
2K(s) + Cl2(g)  2KCl(s)

15. Classifying Reactions
Decomposition Reactions: a single compound is broken down into two or more products
AB  A + B
CaCO3(s)  CaO(s) + CO2(g)

16. Classifying Reactions
Single-Replacement Reactions: atoms of one element replace the atoms of a second element in a compound
A + BX  AX + B
Mg(s) + Zn(NO3)2(aq)  Mg(NO3)2(aq) + Zn(s)
Note: The Activity Series of Metals on p. 293
and the back of your periodic table

17. Classifying Reactions
Double-Replacement Reactions: exchange of positive ions between two reacting compounds…often produce a precipitate, the evolution of gas, or a molecular compound
AX + BY  AY + BX
Na2S(aq) + Cd(NO3)2(aq)  CdS(s) + 2NaNO3(aq)

18. Classifying Reactions
Combustion Reactions: an element or compound reacts with oxygen, often producing energy as heat and light
A + O2  AO2
Complete combustion: produces carbon dioxide and water
Incomplete combustion: C and CO may also be products
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

19. Types of Chemical Reactions