Download chemical reaction

Chemical Reactions
Chemical Reactions
-Chemical change- a change of one or more
substances into other substances
-A chemical change is also known as a
chemical reaction.
Ex.: An iron bar rusts
Signs of a Chemical Reaction
1. formation of a precipitate
precipitate- solid formed that is
different from the reactants
2. a color change occurs
3. formation of a gas (bubbles)
4. energy change: temperature or light
Expressing Chemical Reactions
-Reactions can be expressed as word equations
or as chemical equations.
Ex.: Silver tarnishing (reaction between silver and the sulfur
in air)
Word equation:
silver + sulfur -> silver sulfide
Chemical Equation:
Ag +S8 -> Ag2S
Expressing Chemical Reactions
Ex.: Silver tarnishing (reaction between
silver and the sulfur in air)
Word equation:
silver + sulfur -> silver sulfide
Chemical Equation:
Ag +S8 -> Ag2S
Interpreting Chemical Equations
Ag +S8 -> Ag2S
 - used to separate the products &
reactants; reads produces or yields
+ - separates the different substances on
the reactants or products sides
Interpreting Chemical Equations
Ag +S8 -> Ag2S
Reactants- substances undergoing a change; found
on the left side of the equation
Reactants: Ag & S8
Products- new substance(s) formed; found on the
right side of the equation.
Products: Ag2S
Chemical Symbols
-Symbols are often used in chemical equations to
describe the physical state of reactants and
products.
HC2H2O2 (aq) + NaHCO3(s) --> NaC2H2O2(s) +H2O(l) + CO2(g)
-The symbols in parenthesis indicate the physical
state of each substance.
(s)- solid (l)- liquid (g)- gas (aq)- aqueous
Aqueous- dissolved in water
Determining Physical State
Physical State of Elements:
- Metals: solids at room temperature
*except for Mercury(Hg) it is a liquid
- Nonmetals: solids, liquids or gases
Gases: Noble Gases, H2, N2, O2, F2, &Cl2
Liquids: Bromine (Br2)
Solids: All others
Determining Physical State
Physical State of Compounds
( if not explicitly stated)
- All ionic compounds are solids at room
temperature
- Covalent Compounds can be solids, liquids, or
gases at room temperature:
Common Compounds to know:
H2O- liquid
CO2, CO, NH3, CH4: gases
- All acids are aqueous
Determining Physical States
Aqueous- dissolved in water
-Many chemical reactions are occur when one
or more of the reactants are dissolved in
water; however not all products formed from
aqueous reactions are dissolved in water
-In order for a product to be aqueous it must
be soluble in water; this is determined using
solubility rules.
Determining Physical States: Solubility Rules
1. All common compounds of Group I and ammonium ions
are soluble
2. All nitrate, acetate, and chlorate compounds are soluble.
3. All metal halide (halogen) compounds are soluble, except
those of Ag+, Hg+ & Pb+2
4. All sulfates are soluble except: Ba+2, Sr+2, Ca+2, Pb+2,Ag+,
& Hg+.
5. Carbonate, hydroxides, oxides, silicates, and phosphates
are insoluble, except for those listed in Rule 1.
6. Sulfides are insoluble except for those listed in Rule 1 and
Ba+2, Sr+2, Ca+2, & Mg+2.
DIATOMIC ELEMENTS
Diatomic molecules (X2)
-occur in nature bonded
themselves
Rule of 7:
H
N,O,F
Cl
Br
I
to
Examples
Write the chemical equation for the reaction described below.
Be sure to include the physical states of each substance.
1. When aqueous solutions of Silver nitrate and Potassium
chloride are mixed, potassium nitrate and silver chloride
are produced.
AgNO3(aq) + KCl(aq)  KNO3(aq) + AgCl(s)
2. When sulfuric acid is added dropwise to mossy zinc,
hydrogen and zinc sulfate are produced.
H2SO4(aq) + Zn(s)  H2(g) + ZnSO4(aq)
BALANCING
CHEMICAL EQUATIONS
Balancing
Chemical Equations
Law of Conservation of Mass- matter can neither
be created nor destroyed
For reactions:
Reactants(#’s & types of atoms) = Products(#’s & types of atoms)
Balancing
Chemical Equations
Examples:
H2CO3 (aq) --> H2O (l) + CO2 (g)
H=2
C=1
O=3
H=2
C=1
O=3
Since both sides are equal the equation is said to
be balanced!
Balancing
Chemical Equations
NaOH(aq) + CO2(g) --> Na2CO3(s) + H2O(l)
Na =
O =
H =
C =
1
3
1
1
Na =
O =
H =
C =
2
4
2
1
Since the number of atoms of each element are
not equal the equation is not balanced!
Balancing
Chemical Equations
2NaOH(aq) + CO2(g) --> Na2CO3(s) + H2O(l)
Na =
O =
H =
C =
2
4
2
1
Na =
O =
H =
C =
2
4
2
1
The 2 in front of the NaOH is called a coefficient.
Coefficient- indicates how many units
are involved.
Coefficients are used to balance reactions.
Balancing
Chemical Equations
NaOH(aq) + CO2(g) --> Na2CO3(s) + H2O(l)
Na =
O =
H =
C =
1
3
1
1
Na =
O =
H =
C =
2
4
2
1
Since the number of atoms of each element are
not equal the equation is not balanced!
Balancing
Chemical Equations
NaOH(aq) + CO2(g) --> Na2CO3(s) + H2O(l)
Na =
O =
H =
C =
1
3
1
1
Na =
O =
H =
C =
2
4
2
1
Since the number of atoms of each element are
not equal the equation is not balanced!
Balancing
Chemical Equations
Practice: Balance the following reactions:
1. __Na + __Cl2 --> __NaCl
2. __ZnS + __AlP --> __Zn3P2 + __Al2S3
Note: You cannot change the subscripts because
it will change the identity of the substance.
Balancing and Writing
Chemical Equations (PreAP only)
Write a balanced chemical equation for the reaction
described below.
When solid copper metal is placed in a solution of silver
(I) nitrate, silver metal precipitates out and a solution of
copper (II) nitrate is formed.
Chemical Equation:
Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2
Balanced Chemical Equation:
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2
Types of Chemical
Reactions
Two substances combine to
form 1 product.
A + B → AB
2Na + Cl2 → 2 NaCl
A single compound breaks down
into two or more substances.
AB → A + B
2NaN3 → 2 Na + 3 N2
An element and a compound react to form
a new element & a new compound.
**An element replaces another element in a
compound.
A + BC → AC + B
Zn + 2 HCl --> ZnCl2 + H2
Two compounds react to form two
new compounds.
**The positive ions are exchanged
during the reaction.
AB + CD → AD + CB
NaOH + HCl --> NaCl + H2O
A hydrocarbon plus oxygen yields
CO2 and water.
Hydrocarbon: CxHy
CxHy + O2 → CO2 + H2O
CH4 + O2 --> CO2 + H2O