1. Chemical Reactions

2. Evidence of Chemical Reactions
Chemical Reaction: The process by which the atoms of one or more substances are rearranged to form different substances.
Temperature change
Color change
Gas or solid appears

3. Representing Chemical Reactions
Symbol
Meaning +
Separates two or more products or reactants →
Separates reactants from products
(s)
Solid State
(l)
Liquid State
(g)
Gaseous State
(aq)
Identifies water solution
Chemical Equation
Reactants: substances reacting; on left side
Products: substances produced; on right side

4. Representing Chemical Reactions
How would you write an equation for sodium reacting with chloride to make sodium chloride?
Reactant 1 + Reactant 2 → Product 1
sodium + chloride → sodium chloride
Na (s) + Cl2 (g) → NaCl (s)

5. Representing Chemical Reactions
Law of Conservation of Mass: atoms cannot be created or destroyed.
All atoms in reactants must be in products, and visa versa
Balancing the equation
Na (s) + Cl2 (g) → NaCl (s)
Can not occur without coefficients: number written in front

6. Balancing Equations Write Equation
Count atoms in of elements in reactants
Count atoms of elements in products
Change the coefficients to make # of atoms equal
Write coefficients in their lowest ratio
Check

7. Balancing Equations Na (s) + Cl2 (g) → NaCl (s)
H2 (g) + O2 (g) → H2O (l)
AgNO3(aq) + Cu(s) → CuNO3(aq) + Ag
Al(s) + O2(s) → Al2O3

8. Classifying Chemical Reactions
5 types
Need to be able to recognize different types.
Need to be able to predict products of different types of reactions

9. Synthesis Reactions
A chemical reaction in which two or more substances react to produce a single product.
A + B → AB
Na (s) + Cl2 (g) → NaCl (s)
Compounds combining is also synthesis
CaO(s) + H2O(l) → Ca(OH)2

10. Combustion Reaction
Oxygen combines with a substance to produce heat and energy
2H2(g) + O2(g) → 2H2O(g)
All combustion are synthesis not all synthesis are combustion.

11. Combustion Reaction CH4, methane, is a hydrocarbon
hydrocarbon + oxygen → carbon dioxide + water
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
Can be tough to balance, always balance O2 last.

12. Decomposition Reactions
Single compound breaks down into two or more elements or compounds.
AB → A + B
Often requires an energy source.
NH4NO3(s) → N2O(g) + 2H2O(g)
Air Bags
2NaN3(s) → 2Na(s) + 3N2(g)

13. Single Replacement Reactions
A reaction in which the atoms of one element replace the atoms of another
A + BX → AX + B
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)

14. Double Replacement Reactions
Exchange of ions between two compounds
AX + BY → AY + BX
Ca(OH)2 (aq) + 2HCl (aq) → CaCl2 (aq) + 2 H2O(l)
All double replacement reactions produce either a precipitate, a gas, or water

15. Double Replacement Reactions
Precipitate: a solid being produced during a chemical reaction in a solution
Pair cations with other anion for both compounds
LiI(aq) + AgNO3(aq) →

16. Types of reactions