CHEMICAL
REACTIONS
UNIT - 8
2
Combustion
reactions
A combustion reaction is a chemical
reaction which a fuel undergoes
oxidation by reacting with an
oxidizing agent, resulting in the
release of energy (usually in the
form of heat).
3
4
5
6
7
8
EXOTHERMIC
REACTION
9
10
oxidation reaction
Oxidation is a process in which a
substance either adds oxygen or
removes hydrogen
11
WITH WATER
WITH ACID
12
ENDOTHERMIC
REACTIONS
13
14
Citric acid + sodium hydrogen carbonate
sodium citrate
+ water + carbon
dioxide
15
Ammonium nitrate with water
When ammonium nitrate is dissolved in a beaker containing water, the
beaker becomes cold because it is an endothermic reaction that is it
absorbs energy from the surroundings in the form of heat.
16
17
89,5
18
Reaction of metals with O2
metal + oxygen → metal oxide.
All metals react with oxygen except silver (Ag(s)),
platinum (Pt(s)) and gold (Au(s)). In general, metals
react with oxygen to form metal oxides.
20
Rusting of iron
Rusting is an oxidation
reaction. The iron reacts
with water and oxygen to
form hydrated iron oxide,
which we see as rust.
Iron and steel rust when
they come into contact
with water and oxygen –
both are needed for
rusting to occur.
21
How to prevent rusting of iron ?
Use an Alloy: The use of alloys, like
stainless steel.
Apply Oil: A coating of oil will help to
prevent rust or slow it down, since it
inhibits moisture from reaching the iron in
the metal.
Apply a Dry Coating: Special rust
preventative products dry with no residue
and form a protective barrier over metal
parts and equipment.
Store Properly: Store metal parts or
products in a low-moisture area, or inside a
temperature and humidity-controlled
environment to significantly slow down rust.
Powder Coating: A layer of acrylic, vinyl,
epoxy or other substances will prevent
moisture from reaching the metal, thereby
preventing rust.
Paint the Metal: A good quality paint will
slow down rusting by preventing
moisture from reaching the metal.
22
Galvanization
It is the process of applying
a protective zinc coating to
iron or steel, to prevent
rusting. The most common
method is hot dip
galvanizing, in which steel
sections are submerged in a
bath of molten zinc.
23
Reaction of metals with water
Metal + Water ⇨ Metal hydroxide + Hydrogen
Most of the metals do not react with water. However, alkali
metals react vigorously with water.
Na + H2O ⇨ NaOH + H2
K + H2O ⇨ KOH + H2
Ca + 2H2O ⇨ Ca(OH)2 + H2
Mg + H2O ⇨ MgO + H2
25
2Al + 3H2O ⇨ Al2O3 + 2H2
Zn + H2O ⇨ ZnO + H2
3Fe + 4H2O ⇨ Fe3O4 + 4H2
26
27
Reaction of metals with dilute acid
Metal + dil. acid ⇨ Metal salt + Hydrogen
When a metal reacts with dilute acid, salts are formed.
During this reaction hydrogen gas is evolved.
Some metals reacts vigorously with dilute
sulfuric acid or hydrochloric acid for example,
potassium, sodium, lithium and calcium.
29
Link https://www.youtube.com/watch?v=53T5WZHQ_Ck
30
Ca + 2HCl → CaCl2 + H2
31
Reactivity series of metals
32