1. Chemical Reactions
Chapter 10

4. Reactions and Equations Section 1
The process by which the atoms of one or more substances are rearranged to form different substances is called a chemical reaction (aka chemical change)
Chemical Reaction Indicators
Temperature Change (Release/absorption of energy)
Color change
Odor
Gas formation
Formation of a solid

5. Representing Chemical Reactions
Reactants- starting substances
Products- substances that are formed during the reaction
Reactant 1 + Reactant 2  Product 1 + Product 2
“react to produce” or “yield”
Always written to the arrow’s right
Always written to the arrow’s left

6. Symbols used in Equations
Meaning +
Separates two or more reactants or products 
Separates reactants from products
(s)
Identifies solid state
(l)
Identifies liquid state
(g)
Identifies gaseous state
(aq)
Identifies water solution

7. “Iron and chlorine react to produce iron (III) chloride”
Writing Equations
“Iron and chlorine react to produce iron (III) chloride”
Iron (s) + chlorine (g)  iron (III) chloride (s)
Fe (s) Cl2 (g)  FeCl3 (s)
Chemical Equation- statement that uses chemical formulas involved in a chemical reaction
Shows the number of atoms of each reactant and each product is equal on both sides of the arrow (balanced)

8. Practice Problems
Write skeleton equations for the following word equations
hydrogen (g) + bromine (g)  hydrogen bromide (g)
carbon monoxide (g) + oxygen (g)  carbon dioxide (g)
potassium chlorate (s)  potassium chloride (s) + oxygen (g)

9. Page

10. Steps for balancing equations
Write the skeleton equation for the reaction. Make sure that the chemical formulas are correctly written. Show the physical states of all reactants and products.
Count the atoms of the elements in the reactants. If a reaction involves identical polyatomic ions in the reactants and products, count the ions as they are elements.
Count the atoms of the elements in the products.

11. 4. Change the coefficients to make the number of atoms equal on both sides of the equations. NEVER change the subscript in a chemical formula to balance an equation because doing so changes the identity of the substance.
5. Write the coefficients in their lowest possible ratio. (whole numbers)
6. CHECK YOUR WORK!

12. (The reaction occurs in water)
Practice Problem
Sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide.
(The reaction occurs in water)

13. Organizing Technique
Starting
Add Coefficients
Balanced

14. Practice Problems
Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfate

15. Classifying Chemical Reactions Section 2
Synthesis-whenever two or more substances combine to form a single product
Example: 4Fe(s) + 3 O2(g)  2Fe2O3 (s)
General Equation:
element/compound + element/compound  compound
A B  AB
Combustion- a substance reacts with oxygen to produce carbon dioxide and water
Example: CH4(g) + 2O2(g)  CO2(g) + 2 H2O(g)
Organic Compound + Oxygen  Carbon Dioxide + Water
Organic Compound + O2(g)  CO2 (g) + H2O(g)

16. Combustion reactions- oxygen combines with a substance and releases energy in the form of heat and light

17. Example: NH4NO3(s)  N2O(g) + 2H2O(g)
Decomposition-a compound breaks down into two or more elements or new compounds
Example: NH4NO3(s)  N2O(g) + 2H2O(g)
General Equation: compound  two or more elements/compound
AB  A B
Practice Problems:
The solids aluminum and sulfur react to produce aluminum sulfide.
Ethane gas (C2H6) burns in air, producing carbon dioxide gas and water vapor
Nickel (II) hydroxide (s) decomposes to produce nickel (II) oxide (s) and water.

18. Replacement Reactions
Single Replacement-one element takes the place of another element in a compound
Example: Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s)
General Equation:
element A + compound BX  compound AX + element B A + BX  AX B
HAVE TO USE THE ACTIVITY SERIES TO SEE IF THE METAL WILL BE REPLACED.
IF METAL (A) IS LOCATED ABOVE METAL (B), IT WILL REPLACE IT. (IF NOT, WRITE NO REACTION (NR)

21. Practice Problems K (s) + ZnCl2 (aq)  Cl2 (g) + HF (aq) 
Fe (s) + CuSO4 (aq) 

22. Double-Replacement Reactions
Double Replacement- the positive portions for two ionic compounds are interchanged
Example: Pb(NO3)2 (aq) + 2KI (aq)  PbI2 (s) + 2KNO3 (aq)
General Equation: compound AB + compound CD  compound AD + compound CB
AB + CD  AD + CB
NOTE: A PRECIPITATE OR WATER MUST BE FORMED!! TO PREDICT THIS, USE THE SOLUILITY RULES TO SEE IF A PRECIPITATE IS FORMED, FOLLOW THE DIRECTIONS TO THE CHART FOR THE COMPOUNDS OF THE PRODUCTS FORMED

24. Practice Problems
Aqueous lithium iodide and aqueous silver nitrate react to produce solid silver iodide and aqueous lithium nitrate.
BaCl2(aq) + K2CO3 (aq)

25. Section Assessment What are the five classes of chemical reactions?
Identify two characteristics of combustion reactions.
Compare and contrast single-replacement reactions and double-replacement reactions.

26. Reactions in Aqueous Solutions Section 3
Review: solution = homogeneous mixture
Solutes- the particles dissolved in the solution
Solvent- water (in most cases)- what does the dissolving
Aqueous solution- a solution in which water is the solvent

27. Three types of products form from the DR-reaction
When two aqueous solutions that contain ions as solutes are combined, the ions may react with one another. (double-replacement reaction occurs)
Three types of products form from the DR-reaction
Precipitate (type of solid)
Water
Gas

28. Ionic Equations
Complete Ionic Equation- show all of the particles in a solution as they realistically exist
Spectator Ions- Ions that do not participate in a reaction
Net Ionic Equation- include only the particles that participate in the reaction (forming a precipitate, water and/or gas)

29. Example
Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s)

30. Pb+2(aq)+ 2I-(aq)  PbI2(s)
Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s)
Complete Ionic Equation:
Pb+2(aq)+ 2NO3-1(aq)+ 2K+ (aq)+ 2I-(aq)  2K+(aq) + 2NO3(aq) + PbI2(s)
Cross out spectator ions
3. Net Ionic Equation
Pb+2(aq)+ 2I-(aq)  PbI2(s)

31. Your turn! Aqueous solutions of lithium sulfate and calcium
nitrate are mixed, forming the precipitate calcium sulfate
Steps to remember:
Write out complete balanced (DR) reaction (with states)
Complete ionic equation
Get rid of spectator ions
Net ionic equation