Download + O2 (g)

Chapter 3
Chemical Reactions and
Equations
Chemical Reactions
Reactions involve rearrangement and exchange
of atoms to produce new pure substances.
Reactants
Products
Chemical Equations
Shorthand way of describing a reaction
!
Provides information about the reaction
!
1. formulas of reactants and products
2. states of reactants and products
3. relative numbers of reactant and product molecules
Combustion of Methane
Methane gas reacts with oxygen gas to produce
carbon dioxide gas and gaseous water.!
CH4(g) + O2(g) ➜ CO2(g) + H2O(g)
This equation reads
“1 molecule of CH4 gas combines with 1 molecule of
O2 gas to make 1 molecule of CO2 gas and 1
molecule of H2O gas.”
+
+
What about conservation of mass ??
+
1C + 4H
+
+ 2O
X
1C + 2O
+2H + O
Combustion of Methane, Balanced
To show the reaction obeys the Law of Conservation of Mass,
the equation must be balanced.
CH4(g) + O2(g) ➜ CO2(g) + H2O(g) !
!
CH4(g) + O2(g) ➜ CO2(g) + 2 H2O(g) !
!
CH4(g) + 2 O2(g) ➜ CO2(g) + 2 H2O(g)
+
+
“1 molecule of CH4 gas combines with 2 molecules
of O2 gas to make 1 molecule of CO2 gas and 2
molecules of H2O gas.”
Symbols Used in Equations
Symbols used to indicate state after chemical:
!
(g) = gas; (l) = liquid; (s) = solid
(aq) = aqueous = dissolved in water
!
Energy symbols used above the arrow for
conditions for reactions:
!
Δ = heat
hν = light
shock = mechanical
elec = electrical
Steps in Balancing Equations
1. In compounds balance elements other than H and O.
!
a. Balance elements which occur only once on each side of
the equation.
b. Start with the elements which occur the most.
c. Balance polyatomic ions which do not change in the
reaction.
2. Be prepared to rebalance if something changes!!!
!
3. Balance H.
!
4. Balance O.
!
5. Balance elements which appear in their “elemental” forms.
When aluminum metal reacts with air, it produces a
white, powdery compound, aluminum oxide.!
aluminum(s) + oxygen(g) ➜ aluminum oxide(s)
!
Al(s) + O2(g) ➜ Al2O3(s)
!
2 Al(s) + O2(g) ➜ Al2O3(s)
!
2 Al(s) + 3 O2(g) ➜ 2 Al2O3(s)
!
4 Al(s) + 3 O2(g) ➜ 2 Al2O3(s)
Solid phosphorous (P4) reacts with hydrogen gas to
produce phosphorous trihydride.
P4 (s)
!
P4 (s)
!
P4 (s)
+
H2 (g)
---------->
PH3 (g)
+
H2 (g)
----------> 4 PH3 (g)
+ 6 H2 (g)
----------> 4 PH3 (g)
Solid potassium chlorate decomposes to produce !
oxygen gas and potassium chloride.
KClO3 (s) ------------------->
2 KClO3 (s) ------------------->
!
2 KClO3 (s) ------------------->
O2 (g) + KCl (s)
3 O2 (g) + KCl (s)
3 O2 (g) + 2 KCl (s)
Aqueous sulfuric acid reacts with solid sodium cyanide!
to produce aqueous sodium sulfate and hydrogen cyanide gas.
H2SO4 (aq) + NaCN (s) ------> Na2SO4 (aq) + HCN(g)
!
H2SO4 (aq) + 2 NaCN (s) ------> Na2SO4 (aq) + HCN(g)
!
H2SO4 (aq) + 2 NaCN (s) ------> Na2SO4 (aq) + 2 HCN(g)
Aqueous potassium phosphate reacts with aqueous calcium nitrate!
to produce solid calcium phosphate and aqueous potassium nitrate.
!
!
!
K3PO4 (aq) + Ca(NO3)2 (aq) ----------> Ca3(PO4)2 (s) + KNO3 (aq)
K3PO4 (aq) + 3 Ca(NO3)2 (aq) ----------> Ca3(PO4)2 (s) + KNO3 (aq)
K3PO4 (aq) + 3 Ca(NO3)2 (aq) ----------> Ca3(PO4)2 (s) + 6 KNO3 (aq)
2 K3PO4 (aq) + 3 Ca(NO3)2 (aq) ----------> Ca3(PO4)2 (s) + 6 KNO3 (aq)
Write a balanced equation for the
combustion of butane, C4H10.
C4H10 (g) +
O2 (g) ➝
CO2 (g)
+
H2O (g) ☚
C4H10 (g) +
O2 (g) ➝ 4 CO2 (g)
+
H2O (g)
C4H10 (g) +
O2 (g) ➝ 4 CO2 (g)
+ 5 H2O (g)
!
!
!
C4H10 (g) + 13/2 O2 (g) ➝ 4 CO2 (g)
+ 5 H2O (g)
!
2 C4H10 (g) + 13 O2 (g) ➝ 8 CO2 (g) + 10 H2O (g)
Acetic acid reacts with the metal aluminum to make
aqueous aluminum acetate and gaseous hydrogen
Al(s) + HC2H3O2(aq) ➜ Al(C2H3O2)3(aq) + H2(g)
Al(s) + 3 HC2H3O2(aq) ➜ Al(C2H3O2)3(aq) + H2(g)
Al(s) + 6 HC2H3O2(aq) ➜ Al(C2H3O2)3(aq) + 3 H2(g)
Al(s) + 6 HC2H3O2(aq) ➜ 2 Al(C2H3O2)3(aq) + 3 H2(g)
2 Al(s) + 6 HC2H3O2(aq) ➜ 2 Al(C2H3O2)3(aq) + 3 H2(g)
Organic Chemistry
Classifying Compounds
Organic vs. Inorganic
In the18th century, compounds from living things
were called organic; compounds from the
nonliving environment were called inorganic.
!
Organic compounds easily decomposed and
could not be made in the 18th-century lab.
!
Inorganic compounds were very difficult to
decompose, but could be synthesized.
Modern Classification of Compounds
Organic vs. Inorganic
Today we commonly make organic compounds
in the lab and find them all around us.
!
Organic compounds are mainly made of C and
H, sometimes with O, N, P, S, halogens, and
trace amounts of other elements.
!
The main element that is the focus of organic
chemistry is carbon.
Carbon Bonding in Organic Compounds
Carbon atoms bond almost exclusively
covalently in organic compounds.
!
When C bonds, it forms four covalent bonds.
Carbon is unique in that it can form limitless
chains of C atoms, both straight and branched,
and rings of C atoms.
Classifying Organic Compounds
There are two main categories of organic
compounds, hydrocarbons and
functionalized hydrocarbons.
All chemical
compounds
Inorganic
Organic
Hydrocarbons
Functionalized
Hydrocarbons
Hydrocarbons-Contain only Carbon and Hydrogen
Name
Molecular
formula
methane
CH
propane
C
LP gas
n-butane
C
Butane lighters
n-pentane
C
Gasolines
ethene
C
Polymers
ethyne
C
Welding
Structure
Use
Natural gas
Families of Organic Compounds
C
O
Alkanes
C
C
Aldehydes
H
O
C
C
C
C
C
C
Alkenes
C
C
Aromatics
C
C
O
H
C
O
C
C
O
O
C
C
O
Alcohols
Ethers
Ketones
C
O
Alkynes
C
C
C
Esters
Amines
N
O
C
H
Carboxylic
Acids
N
Amides