Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

CHEMISTRY CHEMICAL REACTIONS AND EQUATIONS

Chemical Reactions and Equations
When a chemical change occurs, a chemical reaction takes place
...




(Reactants)
(Products)
Representation of a chemical reaction with the help of chemical formulae is called a chemical
equation
...

An arrow (→) pointing towards the products is inserted between the reactants and the products
...

A single arrow (→) indicates the direction in which the reaction proceeds
...
e
...

A plus sign (+) is inserted between two or more reactants or products formed
...
, then these
conditions are mentioned on the arrow
...

If gas is liberated as a product then it is represented by an arrow pointing upwards (↑)
...


Balancing the Chemical Equations




In a balanced chemical equation, the total number of atoms of each element of the reactants on the
left hand side of the equation is equal to the number of atoms of the products formed on the right hand
side of the equation
...


www
...
com

2

CHEMISTRY CHEMICAL REACTIONS AND EQUATIONS
Steps Involved in Balancing a Chemical Equation
Consider the chemical reaction between magnesium and oxygen to understand the steps involved in
balancing a chemical equation
...

Magnesium + Oxygen → Magnesium oxide
Step 2
Write the chemical equation for the reaction between magnesium and oxygen
...
H
...
and R
...
S
...

Mg + O2 → MgO
Component

Reactant

Product

Magnesium

1

1

Oxygen

2

1

This is an unbalanced equation
...
Do not change anything inside
the boxes while balancing the equation
...
In that compound,
select the element which has the maximum number of atoms
...
e
...

To balance the oxygen atoms, let us multiply magnesium oxide molecule by 2 on the right hand side
...
Therefore, multiply the magnesium atom by 2 on the left hand side
...
topperlearning
...
On heating, magnesium combines with oxygen
present in air to form magnesium oxide
...


Types of Chemical Reactions
Combination Reaction
When two or more substances combine to form a single product, the reaction is known as a combination
reaction
...

Fe(s) + S(s)  FeS(s)
 Endothermic Reaction: The reactions accompanied by the absorption of heat are called
endothermic reactions
...


Decomposition Reaction
A chemical reaction in which a single compound splits into two or more simple substances is called a
decomposition reaction
...

2HgO(s)
2Hg(s) + O2 ↑
Mercuric oxide
Mercury
Oxygen
 Thermal Decomposition Reaction: The decomposition reactions carried out by heating are known
as thermal decomposition reactions
...

www
...
com

4

CHEMISTRY CHEMICAL REACTIONS AND EQUATIONS
Displacement Reaction
Reactions in which the more reactive element displaces the less reactive element from its compound are
called displacement reactions
...

Zn(s) + CuSO4 (aq)

ZnSO4 (aq) +
Cu(s)
Zinc
Copper sulphate
Zinc sulphate
Copper

Double Displacement Reaction
Reactions in which ions of the reactants exchange places to form two new compounds, are called double
displacement reactions
...

NaOH(aq)
+
HCl(aq)
 NaCl(aq)
+
H2O(l)

Oxidation Reactions
Reactions which involve the addition of oxygen or the removal of hydrogen are called oxidation reactions
...

For example:
Fe2O3
+
3CO
2Fe
+
3CO2↑
Ferric oxide
Carbon monoxide
Iron
Carbon dioxide

Redox Reaction
The chemical reaction in which oxidation and reduction takes place simultaneously is known as a redox
reaction
...
topperlearning
...

For example:
Iron combines with oxygen present in the air, in the presence of water, to form a red-brown flaky
substance called rust
...

The chemical formula of rust is Fe2O3
...


Prevention of Corrosion




Corrosion damages buildings, bridges, ships, automobiles and other articles made of iron
...
This will not only save money but can also prevent the
occurrence of accidents
...


Rancidity





Oils and fats react with oxygen and get oxidised or turn rancid
...

Rancidity can be prevented by keeping food in air tight containers or by using antioxidants
...

Storage of food in air tight containers also decelerates oxidation
...
topperlearning

---