Chemical Equations and Reactions Notes
Name ____________________________
8.1, 8.2, 8.3
Period ________ Date_______________
8.1 Describing Chemical Reactions
A. Chemical Changes and Reactions
1. New substances are _____________________.
2. Chemical reaction – chemical bonds between atoms or ions ______________, and new
____________________ form between atoms or ions.
B. Evidence of a Chemical Reaction
1. ___________________________________________
2. ___________________________________________
3. ___________________________________________
4. ___________________________________________
C. Mechanics of a Chemical Reaction
1. Starting Materials – __________________________
2. Ending Materials - ___________________________
3. _______________________→ ______________________
Arrow = _________________ or ____________________
4. Many reactions occur to complete a set of __________________________________.
5. Symbols above the yield sign represent ______________________ necessary for a reaction to
proceed.
Δ
 = delta = _____________
Ex) 
elec

 = ____________________
6. Some reactions occur ___________________________.
7. Symbols represent the ________________ of the reactants and products.
liquid = ______
gas = _______
solid = ______
crystal = ______
Aqueous = ______ (solids in ____________________________)
Ex)
1
8. Complete chemical equations include the subscript to indicate the physical _______________ of
each substance.
9. Diatomic molecules – certain elements exist in nature as diatomic molecules (X2)
List them:
8.2 Balancing Equations
A. Equations in Chemistry
1. Chemical equation: an expression that uses __________________ and___________________ to
describe a chemical reaction.
2. ____________ means “reacts with.”
3. ____________ means “produces” (called the ______________ sign.)
B. Balancing Chemical Equations
1. Conservation of ____________ leads to balancing equations – the number of atoms of each
element must be the same _____________________________________________________.
2. The Law of Conservation of Mass also states that the total ____________ before and after the
reaction must be the ______________. A reaction cannot lose or gain mass.
3. Therefore the MASS OF THE PRODUCTS = _______________________________________
4. Subscript – indicates number of ______________ of an element present in a compound.
5. Coefficient – indicates the number of ___________ or ___________________ involved in the
reaction.
6. Steps to Balance Equations:
A. Write equation with symbols.
B. Count # of atoms on each side of the reaction.
C. Balance atoms using coefficients.
D. General Rule: Balance all elements first. Then, balance C, H, and O.
E. NEVER CHANGE SUBSCRIPTS!!!!
7. Balance the following equations:
H2
+
Na2SO4
N2
+
→
Ca3(PO4)2
NH3
→
CaSO4
+
Na3PO4
2
NaNO3
→
C8H18
+
NaNO2
O2
→
+
O2
CO2
+
H2O
8.3 Classifying Chemical Reactions
A. Synthesis Reactions (________________________________)
1. Two or more ____________________ or __________________ combine to form a more
__________________ product.
2. Ex.
A + B → AB
Fe + S → FeS
CaO + H2O
→
Ca(OH)2
Sodium reacts with chlorine
B. Decomposition Reactions (______________________)
1. A _______________ reactant breaks down into _________________ compounds or elements.
AB → A + B
2. The ________________ of a synthesis reaction.
3. Carbonates (compounds ending in_________) break down into ________________________ and
_______________________________.
HgO
4. Ex.
→
CaCO3
→
C. Single Replacement Reactions
1. Atoms of an uncombined element _________________ atoms of another element in a compound.
A + BX →
AX + B
2. A ____________ active element will replace a less active element. (see Activity Series handout.)
3. An Activity Series is a way of _________________ elements (usually metals) in order from
greatest to least reactivity. It can be used to ______________ whether a reaction will occur or not.
Al +
CuSO4 →
PbSO4 +
Au
→
Fe +
MgCl2 →
AgCl2 +
Cu →
3
D. Double-Replacement Reactions
1. Atoms or ions from two___________________ compounds replace each other.
AX + BY
→
AY + BX
2. These types of reactions will (A) form __________________ (↓), (B) form ___________ (↑) or
(C) are __________________ neutralizations.
A. Pb(NO3)2 + KI →
B. CaCO3 + HCl →
C. NaOH +
HCl →
3. In letter B above, carbonic acid, H2CO3, is unstable and will immediately decompose into
_______________________________ and __________________.
E. Combustion Reactions
1. One substance reacts with _____________________ to produce oxide compounds.
2. This occurs during _________________ or _____________________ (rusting.)
3. The reactions that only add oxygen are classified as ____________________ reactions.
Ex)
S
+
→
O2
SO2
4. Combustion reactions are _____________________, releasing a large amount of energy as light,
heat, or sound.
5. A true Combustion reaction occurs when a________________________ (a compound containing
______ & _____) reacts to form __________________________ and ______________ which are
always the products.
CxHx +
6. Ex. ____CH4 + ____O2
→
C6H12O6
→
+
O2
O2
→ CO2 + H2O
____CO2 + ____H2O + 803 kJ
4