1. Chapter 8
Chemical Reactions

2. Reactants Products + - separates reactants and products - “yields”
- reversible reaction
(s) - solid
(l) - liquid
(g) - gas

3. (aq) – aqueous solution, dissolves in H2O
- heat
Pt catalyst

4. Examples
Fe (s) O2 (g) Fe2O3 (s)
4Fe (s) O2 (g) Fe2O3 (s)

5. Balancing Chemical Equations
Balanced equations obey the law of conservation of matter.
Balanced Equation – must have the same number of atoms of each element in both sides of the equation.

6. Examples
C(s) O2(g) CO2(g)
1 C O C + 2O

7. More Examples
2C(s) O2(g) CO
2C O C 2O

8. Rules for Balancing Equations
1) Determine the correct formulas for reactants and products
2) Write the reaction
3) Count the number of atoms of each element in the reactants and products (a poly-atomic ion appearing unchanged on both sides of the equation is counted as a single unit)

9. Rules Cont’d 4) Balance elements 1 at a time using coefficients
Coefficient: small whole # that appears in front of a formula in an equation
Balance O & H last
You cannot change subscripts

10. Rules Cont’d 5) Check to see if each atom is balanced
6) Make sure Coefficients are lowest possible numbers

11. Example
H2 + O H2O
4H O H2O

12. Combination Reactions
Two or more substances react to form a single substance

13. Formation of Binary Salts
M X MX
Example
2Na + Cl NaCl

14. Formation of Binary Oxides
M O MO
Example
2Zn + O ZnO

15. Formation of Binary Acids
Examples
H2 + X HX
H2 + Cl HCl

16. Formation of Ternary Acids
Examples
H2O + nonmetallic oxide oxyacid
P2O5 + 3H2O H3PO4

17. Formation of Bases
Examples
MO + H2O MOH
CaO + H2O Ca(OH)2

18. Formation of Ternary Salts
Examples
MO XOn MXOn+1
CaO CO CaCO3

19. Decomposition Reactions
A single compound is broken down into 2 or more simpler products.
A B + C
CaCO CaO + CO2
They can be a combination of elements and compounds

20. Decomposition reactions require energy - (heat, light or electricity)
Binary Compounds break down into constituent elements
Decomposition reactions require energy - (heat, light or electricity)
Example
2H2O(l) electricity 2H2(g) + O2(g)

21. Single Replacement Reactions
Atoms of an element replace the atoms of a second element in a compound
Gen Rxn:
A + BC AC + B
Example
Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

22. How do you know this will happen?
Whether one metal will replace another is determined by the relative activity of the 2 metals.

23. Activity Series Lists metals in order of decreasing reactivity
A positive metal will replace any metal found below it in the activity series
Metals from Li to Na replace H from acids and H20; Mg to Pb replace H from acids only.

24. Double Replacement Rxns
Involve an exchange of positive ions between two compounds.
Generally take place in aqueous solutions

25. For a double displacement rxn to occur one of the following must be true:
A precipitate forms
A gas forms and bubbles out of mixture
A molecular compound forms (ie H2O)

26. Examples
AB + CD AD + CB
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

27. Combustion Rxns Example CxHy + O 2 CO2 + H2O
Oxygen reacts with another substance, producing energy in the form of heat or light.
Example
CxHy + O CO2 + H2O