Download Gas-Forming reactions Reactions that form a

CHAPTER 5 – REACTIONS AND AQUEOUS SOLUTION – PART 2
Gas-Forming reactions
Reactions that form a gas as one of the products are gas-forming reaction.
Most common examples involve metal carbonates and acids.
CaCO3 + 2CH3COOH(aq) → Ca(CH3COO)2(aq) + H2CO3(aq)
H2CO3(aq) →
Overall equation
Ionic equation:
Net ionic equation:
Combustion Reactions
In a combustion reaction, a fuel is reacted with oxygen to make oxides.
Combustion reactions are ________________; however, they still require
energy input to get started.
In most combustion reactions, the fuel is a hydrocarbon (CxHy). Other
possible fuels include S8 and NH3:
When the fuel is a hydrocarbon, there are two different types of combustion,
complete and incomplete.
1.
In complete combustion, there is enough oxygen available to make
carbon dioxide from all of the carbon atoms:
e.g. CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)
2.
If there isn’t enough oxygen available for complete combustion,
carbon monoxide is produced. This is incomplete combustion:
e.g. 2 CH4(g) + 3 O2(g) → 2 CO(g) + 4 H2O(g)
If 2 moles of octane (C8H18(l)) are burned with 17 moles of oxygen gas, is
that an example of complete or incomplete combustion?
Oxidation-reduction reactions (Redox reactions)
The reactions we have seen thus far are exchange reactions, in which the
ions of the reactants changed partners.
A+B¯ + C+D¯ → A+D¯ + C+B¯
But they end up with the same number of electrons they start with.
Every atom, ion or polyatomic ion has a formal oxidation number
associated with it. This value compares the number of protons in an atom
(positive charge) and the number of electrons assigned to that atom (negative
charge).
In many cases, the oxidation number reflects the actual charge on the atom,
but there are many cases where it does not. Think of oxidation numbers as a
bookkeeping exercise simply to keep track of where electrons go.
There are rules to help you determine the oxidation number.
1. The oxidation number for an element in its elemental form is 0
2. The oxidation number of a monoatomic ion is the same as its charge
3. In binary compounds, the element with greater electronegativity is
assigned a negative oxidation number equal to its charge in simple ionic
compounds of the element.
(a). Fluorine always has oxidation number of -1.
(b). Cl, Br and I has an oxidation number of -1 in compounds, except when
combined with oxygen or fluorine
(c). Hydrogen, in all its compounds except hydrides, has an oxidation
number of +1.
(d). Oxygen, in all its compounds except when connected to another
oxygen or a fluorine, has an oxidation number of -2.
(e). Alkali metals always have an oxidation number of +1 and alkaline
earth metals +2.
4. The sum of the oxidation numbers is zero for an electrically neutral
compound and equals the overall charge for an ionic species.
HCl
ClO¯
KMnO4
Na2SO3
F2O
CH4
CCl4
HClO4
Oxidation – loss of electrons (oxidation number increases)
Reduction –gain of electrons (oxidation number decreases)
A redox reaction is one in which atleast one atom loses electrons, while
another gains electrons. It is important to identify which is oxidized and
which is reduced
An easy way to remember oxidation – reduction is:
LEO the lion says ‘GER’
In the following reaction:
2 Na(s) + Cl2(g) → 2NaCl
Which atom is oxidized?
Which atom is reduced?
Oxidation state of sodium changes from ____ to ____
Oxidation state of chlorine changed from ____ to ____
In reaction,
Fe2O3(s) + 3CO(g) →2Fe(s) + 3 CO2(g)
Oxidation state of Fe changes from _____ to ____
Oxidation state of C changes from ____ to ____
_____ is responsible for reduction of ____. Hence it is called a reducing
agent. The reducing agent gets oxidized in the process.
An oxidizing agent aids in oxidation of a substance and it gets reduced in
the process.
2 Mg(s) + O2(g) →2 MgO(s)
Which is the oxidizing agent?
Half reactions
In every oxidation – reduction reaction, one reactant is reduced (therefore it
is an oxidizing agent) and one reactant is oxidized (reducing agent). We can
show this by dividing the redox reaction into two half-reactions:
Redox reaction: X + Y →Xn+ + YnHalf reaction 1: X → Xn+ + ne¯
Half reaction 2: Y + ne¯→ YnIdentify the type of following reactions:
1. NaOH
+ HNO3
2. Pb(NO3)2
3. Cu
+ KCl
+ HNO3
→ NaNO3
→ PbCl2
→ Cu(NO3)2
+ H2 O
+ KNO3
+ NO2 + H2O
Summary of common reaction types in aqueous solution
Reaction type
Driving force
Precipitation
Formation of an insoluble compound
Acid–base (neutralization)
Formation of a salt and water; proton transfer
Gas–forming
Evolution of a water-insoluble gas such as CO2
Oxidation–reduction
Electron transfer
Important Concepts from Chapter 5
• Electrolytes
• Solubility
o Role of Polarity
o Ksp
o Miscible vs. Immiscible
• Reaction Types
o Precipitation Reactions
o Gas Forming Reactions
o Combustion Reactions (Complete and Incomplete)
o Acid-Base Reactions
o Redox Reactions
• Lewis vs. Brönsted vs. Arrhenius Definitions of Acids/Bases
• Strong Acids/Bases vs. Weak Acids/Bases
• Acidity/Basicity of Oxides
• pH and pOH
• Assigning Oxidation States
• Net Ionic Equations