1. Chapter 8 - Chemical Equations and Reactions

2. Describing Chemical Reactions
Chemical Reaction – process in which one or more substances are changed into one or more different substances
Reactants – original substance
Products – resulting substance
Described by Chemical Equations
Chemical equation – represents, with symbols and formulas, the identities and molar amounts of the reactants and products in a chemical reaction
(NH4)2Cr2O7 (s)  N2 (g) + Cr2O3 (s) + 4H2O

3. Physical Indicators
To know that a chemical reaction has taken place requires evidence that one or more substances have undergone a change in identity.
Release of heat and light
Color change
Production of gas (bubbles)
Form a precipitate
Solid that is produced as a result of a chemical reaction in solution

4. Chemical equations must satisfy the Law of Conservation of Mass
The equation must contain the correct formulas for the reactants and products
The law of conservation of mass must be satisfied
Same number of atoms of each element must appear on each side of the correct chemical equation
Coefficient – small whole number that appears in front of a formula in a chemical equation

5. Writing Word Equations
An equation in which the reactants and products in a chemical reaction are represented by words
Arrow  “react to yield” “yield” “produce” “form”
Example: When methane burns it is combined with oxygen to produce carbon dioxide and water:
Methane + oxygen  carbon dioxide + water

6. Formula Equations What is it?
Represents the reactants and products of a chemical reaction by their symbols and formulas
CH4 (g) + O2 (g)  CO2 (g) + H2O (g) (not balanced)
Why is this not correct? What law does it break?

7. Chemical equations MUST be balanced
Balancing an equation
Relative amounts of reactants and products represented in the equation must be adjusted so that the numbers and types of atoms are the same on both sides of the equation
Carried out by inserting coefficients

8. HOW? __ CH4 (g) + __ O2 (g)  __ CO2 (g) + __ H2O (g)
Count atoms of elements that only appear once on each side of the equation (usually leave H and O for last)
C atoms: _______  _______
H atoms: _______  _______
O atoms: _______  _______
Add any coefficient necessary to balance the atoms for each element individually
C is balanced.
Add a ______ in front of H2O
Add a ______ in front of O2
Count atoms to be sure the equation is balanced

9. Practice

10. 5 types of Chemical Reactions
Synthesis
Decomposition
Single-displacement
Double-displacement
Combustion

11. Synthesis Two or more substances combine to form a new compound:
A+ X  AX
A and X can be elements or compounds; AX is compound
Ex: 2Mg(s) + O2(g)  2MgO(s)

12. Synthesis Practice
Na + Cl2 
Al(s) + O2 

13. Decomposition
A single compound undergoes a reaction that produces two or more simpler substances:
AX  A + X
A and X can be elements or compounds; AX is compound
Ex: CaCO3(s)  CaO(s) + CO2(g)
I will always give you the products for decomposition

14. Single Displacement Reaction
One element replaces a similar element in a compound:
A + BX  AX + B OR Y + BX  BY + X
A, B, X and Y are elements; AX, BX and BY are compounds
Rule of thumb: cation will replace cation or anion will replace anion

15. Single Displacement Reaction Examples
Displacement of Metal with another Metal:
2Al(s) + 3Pb(NO3)2(aq)  3Pb(s) + 2Al(NO3)3(aq)
Displacement of Hydrogen in Water by a Metal:
2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)
Displacement of Halogens:
Cl2(g) + 2KBr(aq)  3KCl(aq) + Br2(l)

16. Activity Series of Elements
What is it?
A list of elements organized according to the ease with which the elements undergo certain chemical reactions
How does it help?
Helps you determine what substances will displace others in chemical reactions
Used in single and double displacement reactions

17. Activity Series of Elements
2Al + 3ZnCl2  3Zn + 2AlCl3
Al is more reactive than Zn (higher on the activity series), so Al can replace Zn
Co + 2NaCL  no reaction
Co is less reactive than Na (lower on the activity series), so it can not replace Na
Cd + Pb(NO3)2 
Cu + HCl 

18. Single Displacement Practice
Ca + H2O 
KI + Br2 
Zn + HCl 

19. Double Displacement Reaction
The ions of two compounds exchange places in an aqueous solution to form two new compounds
AX + BY  AY + BX
A, B, X and Y are ions; AY, BX are ionic compounds
Rule of thumb: The cation and the anion of both compounds will switch

20. Double Displacement Reaction Examples
Formation of precipitate:
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
Formation of a Gas
FeS(s) + 2HCl(aq)  H2S(g) + FeCl2(aq)
Formation of water:
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
As you can see in all examples the _________
and the ________ switch places

21. Double Displacement Practice
AgNO3 + NaCl 
FeS + HCl 
H2SO4 + KOH 

22. Combustion Reaction
A substance combines with oxygen, releasing a large amount of light and heat (always results in production of carbon dioxide and water vapor)
C3H8(g) + 5O2(g)  3CO2(g)+ 4H2O(g)

23. Combustion Reaction Practice
CH4 + O2 
C3H8 + O2 

24. Type of Reactions Review
Classify type of reaction
N2 + 3H2  2NH3
2Li + 2H2O 2LiOH + H2
2NaNO3  2NaNO2 + O2
2C6H O2  12 CO2 + 14H2O

25. Net Ionic Equations
Net ionic equation: includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution
Step 1: Convert chemical equation into a complete ionic equation
All soluble ionic compounds (aq) are shown as dissociated ions
The precipitates are shown as solids
Ex: NaCl(aq) + AgNO3(aq) ---> AgCl(s) + NaNO3(aq)
Na+(aq) + Cl¯(aq) + Ag+(aq) + NO3¯(aq) ---> AgCl(s) + Na+(aq) + NO3¯(aq)

26. Net Ionic Equations
Spectator Ions: ions that do not take part in a chemical reaction and are found in solution before and after reaction
Step 2: Cross out all spectator ions
Ex: NaCl(aq) + AgNO3(aq) ---> AgCl(s) + NaNO3(aq)
Na+(aq) + Cl¯(aq) + Ag+(aq) + NO3¯(aq) ---> AgCl(s) + Na+(aq) + NO3¯(aq)
Cl¯(aq) + Ag+(aq) ---> AgCl(s)

27. Solubility Rules
Soluble – ability of a compound to dissolve in a liquid solution

28. Net Ionic Equation Examples
Pb(NO3)2(aq) + Na2S(aq) --->
ammonium phosphate + calcium chloride --->

29. Write word and formula equations:
Solid sodium oxide is added to water at room temperatures and forms sodium hydroxide.
Word equation:
Formula equation:
Balanced formula equation:

30. Practice
Solid aluminum carbide, Al4C3 reacts with water to produce methane gas and solid aluminum hydroxide.
Word equation:
Formula equation:
Balanced formula equation: