PHYSICAL CHEMISTRY
Assignment - 01
SEPTEMBER 23, 2023
MUNTACIR PARVES
BMB- 34
Rate of Reaction
Definition: The rate of reaction can be define as the change
of concentrations of product or reactant in per unit time. It
can be written as (ROR).
The Rate of Reaction is depend on
 How fast the reactant are being used.
 And how fast the products are being formed.
In other word the
𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 𝑢𝑠𝑒𝑑 (𝑚𝑜𝑙𝑒 /𝑐𝑚2 /𝑔)
ROR=
𝑇𝑖𝑚𝑒 ℎ𝑎𝑠 𝑡𝑎𝑘𝑒𝑛 (sec)
or
𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 𝑓𝑜𝑟𝑚𝑒𝑑 (𝑚𝑜𝑙𝑒 /𝑐𝑚2 /𝑔)
ROR=
𝑇𝑖𝑚𝑒 ℎ𝑎𝑠 𝑡𝑎𝑘𝑒𝑛 (sec)
As example; 25g Caco3 dissolve is water in 2 mint.
 Then the Rate of reaction of Caco3 is
ROR =
25𝑔
120𝑠𝑒𝑐
=0.2283 g/sec
Chemical Equilibrium
Definition: The chemical equilibrium can be define as
the state of reversible reaction when the two
opposing reaction occur at a same rate and the
concentration of product or reactant don’t change
with time.
As example:
N2+3H2 ⇆2NH3
When the N2 Gas and H2 Gas are mixed in a closed containers,
the reaction proceed forming NH3. When the reaction
happens, then the concentration of N2 Gas and H2 Gas are
decreased and the product that formed NH3 its concentration
increases.
In a certain state the forward and backward reaction occur
at a same rate and the concentration don’t changes its stay
constant. And this point is as known as chemical equilibrium.
In this state the reactant and product concentration
remain constant but the forward and revers reaction is
occurring in same rate and this the explanation of chemical
Equilibrium.
Law of Mass Action
The law of mass action state that the rate of chemical
reaction directly proportion to the active mass /molar
concentration of the reactants.
PCl3+Cl2 ⇄
If
PCl5
The rate of forward reaction is
(RoRf) = [PCl3] [Cl2]
(RoRf) ∝ k1 [PCl3] [Cl2]
The rate of backward reaction is
(RoRb) = [PCl5]
(RoRb) ∝ k2 [PCl5]
At equilibrium,
RoRf=RoRb
K1 [PCl3] [Cl2] = k2 [PCl5]

𝐾1
𝑘2
[PCl5]
=
 𝑘𝑐 =
[PCl3] [Cl2]
[PCl5]
[PCl3] [Cl2]
In this equation (𝑘𝑐 ) is the chemical equilibrium constant.
The [PCl3] [Cl2] is the concentration of Reactant & the
k2 [PCl5] is the concentration of product.
The end.
By Muntachir Parves, BMB-34