1. Chapter 9
Chemical Reactions

2. Reactions and Equations 9.1
A chemical reaction is another name for chemical change.
How to tell if a chemical reaction has taken place
Is there evidence? (Temperature change, color change, odor, gas bubbles, general appearance)
Equations are used to represent chemical reactions
Show reactants: the starting substances
Show Products: resulting or ending substances
Do not show numerical values so arrow is used instead of an equals sign
Show indicator of chemical state

3. Types of Equations Three types of equations Word equations
Skeleton
Chemical
Word equations
Used to indicate the reactants and products of chemical reactions
Uses the actual names of the substances involved
Setup: Reactant 1 + Reactant 2  Product 1
Ex: Iron(s) + Chlorine(g)  Iron(III) Chloride(s)
Skeleton Equations
Uses chemical formulas to represent the substances unlike the word equation
Chemical formulas take the place of the words
Iron(s) + Chlorine(g)  Iron(III) Chloride(s) would become:
Fe(s) + Cl2(g)  Fe Cl3(s)

4. Balancing Chemical Equations
Uses chemical formulas like the skeleton equation
Shows matter is conserved during a reaction (Law of Conservation of Mass)
Chemical eqation: Uses identities and relative amounts of the substances involved in a chemical reaction
Everything is balanced in a chemical equation
Fe(s) + Cl2(g)  Fe Cl3(s) would become:
2Fe(s) + 3Cl2(g)  2Fe Cl3(s)
Balancing Chemical Equations
Finding the correct coefficients for chemical formulas in the skeleton equation is very important
Coefficient is usually a whole number and 1 is understood

5. Steps to Balance a Chemical Equation
1: Write the skeleton equation
2: Count the atoms of elements in the reactants
3: Count the atoms of elements in the products
4:Change the coefficients to make both sides of the equation equal
5:Write the coefficient(s) in the lowest ratio possible
6:Check your work
Ex: H2 (g) + O2(g)  H2O(g)
4H2 (g) + 2O2(g)  4H2O(g)
2H2 (g) + O2(g)  2H2O(g)

6. Classifying Chemical Reactions 9.2
There are five types of chemical reactions.
Synthesis
Combustion
Decomposition
Single-Replacement
Double-Replacement
Synthesis Reaction
Chemical reaction in which two or more substances combine to form one single product.
A + B  AB
Ex: 2Na(s) + Cl2(g)  2NaCl(s)

7. Decomposition reactions
Combustion Reaction
Oxygen combined with a substance releasing energy in the form of light and heat
Many combustion reactions are also synthesis reactions
Ex: 2H2(g) + O2  2H2O(g)
Decomposition reactions
Only one compound
Breaks down into 2 or more compounds or elements
Setup: AB A + B
Often requires an energy source (i.e. heat, light, electricity)
Ex: NH4NO3(s)  N2O(g) + 2H2O(g)
The above reaction occurs when the reactant is heated
Replacement Reactions
Unlike the other reactions, replacement reactions involve the replacement of an element in a a compound
2 kinds of replacement reactions:
Single
Double

8. Single Replacement reactions
When atoms of one element replace the atoms of another element in a compound
Setup: A+ BX  AX + B
Whether or not a metal will replace another metal or any other substance depends on the reactivity it has
Double Replacement reactions
Invovles the exchange of ions between 2 compounds
Setup: AX + BY  AY + BX
If a solid is produced during the reaction it is called a precipitate

9. Reactions in Aqueous Solutions 9.3
Vocab
Aqueous solution- Solution in which the solvent is water
Solvent- The water in the solution
Solute- The compound dissolved in the water
Precipitate- Solid formed in a chemical reaction
Spectator ion- Ions that do not participate
Complete ionic equation- Shows all particles as they really exist
Net ionic equation- Only includes particles that participate (No spectator ions)

10. Aqueous Solutions
When two aqueous solutions react it is always a double replacement reaction.
The water doesn’t react
There are three possible products when aqueous solutions react, they are; precipitates, water, or gases.
Spectator ions do not participate in the reaction and are usually not included in the ionic equation.

11. Writing Ionic Equations
Ionic and chemical equations differ in that substances that are ions in the solution are written as ions in the equation.
To write an ionic equation you must show the reactants and the product as ions.
A complete ionic equation shows all of the particles in the solution as they realistically exist.
A net ionic equation is a simplified version of the complete ionic equation. It only shows particles that participate in the reaction.
To write a net ionic equation from a complete ionic equation cross out all spectators.

12. Ionic equations What type of reaction is this?
AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
What type of reaction is this?
A complete ionic equation shows dissolved ionic compounds as their free ions.
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)

13. Ionic Equations
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
Ions that are not directly involved in a reaction are called spectator ions.
Rewriting the equation, leaving out the spectator ions, gives us the net ionic equation…
Ag+(aq) + Cl-(aq)  AgCl(s)

14. Ionic Equations
You also have to make sure that the net charge is balanced. For example…
Pb(s) + 2Cl-(aq)  PbCl2(s)

15. Examples HCl(aq) + ZnS(aq)  H2S(g) + ZnCl2(aq)
Cl2(g) + NaBr(aq)  Br2(l) + NaCl(aq)