1. What indicates a chemical reaction has taken place?
Warmup
What indicates a chemical reaction has taken place?

2. Indicators of chemical change
Bubbles (Most of the time)
Solid forms (precipitate)
Change in temperature
Change in color
Change in properties (particularly smell)

3. 4.1 Chemical Reactions

4. calcium + oxygen → calcium oxide
Chemical Reactions
Chemical Reaction- a process in which physical and chemical properties of the original substance change as existing bonds are broken and new bonds are formed giving new substances with different physical and chemical properties.
HCl + NaOH → H2O + NaCl
Reactants Products
Word Equations
calcium + oxygen → calcium oxide
Formula Equations
Ca + O2 → CaO

5. Remember your diatomic elements!
Diatomic- element that always occurs in pairs
Br2, I2, N2, Cl2, H2, O2, F2
All other elements will be found as a single atom.

6. 2 or more reactants form one product.
Types of Reactions
Synthesis
Decomposition
Single-Replacement
Double-Replacement
Combustion
Synthesis
2 or more reactants form one product.
A + B → AB
Examples:
2H2 + O2 → 2H2O
CaO + H2O → Ca(OH)2

7. Decomposition One reactant forms 2 or more products. AB → A + B
Examples:
2HgO → 2Hg + O2
2NaCl → 2Na + Cl2
Single-Replacement
A single element and a compound become a different element and compound.
A + BX → AX + B
Examples:
Zn + H2SO4 → ZnSO4 + H2
2NaBr + Cl2 → 2NaCl + Br2

8. Example: C2H5OH + 3O2 → 2CO2 + 3H2O
Double-Replacement
2 compounds become 2 different compounds
AX + BY → AY + BX
Examples:
HNO3 + NaOH → NaNO3 + H2O
NH4Cl + NaOH → NaCl + NH4OH
Combustion
An element or compound (generally a hydrocarbon) reacts with oxygen producing carbon dioxide, water, and heat.
Example:
C2H5OH + 3O2 → 2CO2 + 3H2O

9. Balancing Reactions 1. Write the equation
Law of Conservation of Matter indicates that the number of atoms of each type of element must be the same in the reactants and the products
1. Write the equation
CH4 + O2 → CO2 + H2O
2. Assign each substance a variable
a b c d
3. Write equations for each element present
For carbon: a=c
For hydrogen: 4a=2d
For oxygen: 2b=2c+d
4. Set a=1 and solve for all variables.

10. Balancing Reactions 1. Write the equation
CH4 + O2 → CO2 + H2O
2. Assign each substance a variable
1 CH4 + 2 O2 → 1CO2 +2 H2O
a b c d
CH4 + 2 O2 → CO2 +2 H2O
a b c d
3. Write equations for each element present
For carbon: a=c
For hydrogen: 4a=2d
For oxygen: 2b=2c+d
4. Set a=1 and solve for all variables.
Final
Answer

11. Sample Problems
1. Copper(II) Oxide will decompose into copper and oxygen when heated strongly. Write the reaction.
2. Zinc reacts with silver nitrate to produce silver and zinc nitrate. Write the reaction.
What type of reaction is this?

12. Sample Problems
3. Write a balanced chemical equation for the reaction in which aluminum reacts with oxygen to produce aluminum oxide.
4. Write a balanced chemical equation for the reaction in which hydrochloric acid reacts with calcium carbonate to produce calcium chloride, water, and carbon dioxide.