1. Chapter 8
Chemical Reactions
and Equations

2. What does a chemical formula represent?
The elements contained in a chemical substance
Indicates the number of atoms of the element just to the right of the element symbol
a whole number that appears in front of a formula in a chemical equation.
What is a subscript? What does it indicate?
What is a coefficient?

3. Coefficient means 2 molecules
Chemical Formulas
2 C8H18
Coefficient means 2 molecules
indicates there are 8 Carbon atoms in the molecule
indicates there are 18 hydrogen atoms in the molecule

4. Visualizing Compounds Example: H2O
H atoms = ________ O atoms = ________ Model of H2O: 1

5. What is a diatomic element?
An element that is made up of two atoms when it is by itself
H2 O2 F2 Br2 I2 N2 Cl2
Hydrogen Molecule Oxygen Molecule

6. DIATOMIC ELEMENTS
You can also mark them off on your periodic table as the SUPER SEVEN! 7

7. Symbolizes or represents a chemical reaction
When bonds are broken and new bonds are formed producing a new substance
Chemical Equation
Symbolizes or represents a chemical reaction

8. Original substances in a chemical reaction
Reactants
Original substances in a chemical reaction
Products
Substances formed in a chemical reaction
REACTANTS yields PRODUCTS

9. H2 + O2  H2O Reactants Product
Igniting a mixture of hydrogen and oxygen will form water. The symbol equation is:
H O2  H2O
Reactants
Product

10. How does a chemical reaction occur?
Atoms must collide for the reaction to occur
Atoms are rearranged in a chemical change
- None are lost
- None are gained

11. any reaction that gives off heat
Exothermic Reaction
any reaction that gives off heat
Example:
2H2 (g) + O2 (g) H2O (l) + heat

12. heat + 2HgO (s) 2Hg (l) + O2 (g)
Endothermic Reaction
any reaction in which heat is added
Example:
heat + 2HgO (s) Hg (l) + O2 (g)

13. Evidence of a Chemical Change
Color change (THAT YOU DID NOT CAUSE!!)
Temperature change
Formation of a gas
Change in odor
Formation of a precipitate
precipitate: insoluble solid that separates out of solution

14. Balancing Chemical Equations Notes

15. A Chemical Reaction Potassium Iodide [KI] Lead Nitrate [Pb(NO3)2]
Final Product

16. Did a chemical change occur? How do you know?
Is matter conserved in this reaction?

17. According to the LAW OF CONSERVATION OF MATTER, the total atoms of reactants must equal the total atoms of products for any given chemical reaction.
When you have a chemical reaction, you must add coefficients to balance the reaction!

18. UNBALANCED! __H2 + __O2  __H2O Reactant Side Product Side 2 2 2 1
Atom Inventory
__H __O2  __H2O
Reactant Side
Product Side
Atom Type
Number of Atoms H O
UNBALANCED! 2 2 2 1

19. To balance an equation, coefficients CAN be added in front of products or reactants. DO NOT CHANGE SUBSCRIPTS!

20. BALANCED! New Atom Inventory 2 2 __H2 + __O2  __H2O Reactant Side
Product Side
Atom Type
Number of Atoms H O
BALANCED! 4 4 2 2

21. Balancing Equations
___ Mg + ___ N2 ---> ___ Mg3N2 ___ H2S + ___ Cl2 ---> ___ S8 + ___ HCl ___ Al + ___ HCl ---> ___ AlCl3 + ___ H2 ___ Fe2O3 + ___ CO ---> ___ Fe + ___ CO2

22. Classifying Chemical Reactions

23. A + X AX Synthesis Two or more reactants combine to form ONE product.
(marriage)
A + X AX
example:
2Mg (s) + O2 (g) 2MgO (s)

24. AX A + X Decomposition ONE reactant breaks down into smaller parts.
(divorce)
AX A + X
example:
2H2O (l)  2H2 (g) + O2 (g)

25. A + BX B + AX Y + BX X + BY Single Displacement
A single element replaces an element that is part of a compound.
(affair)
A + BX B + AX
Y + BX X + BY
example:
2 Al(s) + 3 Fe(NO3)2(aq) Fe(s) + 2 Al(NO3)3(aq)

26. AX + BY AY + BX Double Displacement
Ions from two different compounds exchange places to form two new compounds.
(wife swap)
AX + BY AY + BX
2KI(aq) + Pb(NO3)2 (aq) PbI2 (s) + 2KNO3 (aq)

27. Combustion
A compound (usually a hydrocarbon) reacts with oxygen, releasing carbon dioxide and water.
AB + O CO2 + H2O
example: combustion of propane
C3H8 (g) + 5O2 (g) CO2 (g) + 4H2O (g)

28. Writing Chemical Reactions Notes

29. a word equation is qualitative
Word Equations
word equation: equation in which the reactants and products in a chemical reaction are represented by words
a word equation is qualitative
example:
methane + oxygen carbon dioxide + water

30. a formula equation is quantitative
Formula Equations
formula equation: represents the reactants and products of a chemical reaction by their symbols or formulas
a formula equation is quantitative
example:
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

31. Symbols in a Chemical Reaction