CHEMICAL KINETICS CLASS- XII. VINAY KUMAR PGT CHEMISTRY KV NTPC KAHALGAON PATNA REGION. It is the branch of physical chemistry which deals with the study of the rate of a chemical reaction and the mechanism by the reaction occur.
CHEMICAL KINETICSCLASS- XII
KV NTPC KAHALGAON
Rate of reaction =Decrease in the concentrationof R
Or Increase in the concentrationof P
Unit of rate is Mol L-1 S-1 or atm S-1 (For gaseous reaction)
Or Rate of reaction = -R] = +P]
Instantaneous rate = -dR] = +dP]
For a general chemical reaction
aA + bB cC + dD
Rav. = -1 A] = -1 B] = 1 C] = 1 D]
a t b t c t d t
Rinst. = -1 dA] = -1 dB] = 1 dC] = 1 dD]
a dt b dt c dt d dt
For a hypothetical reaction
A + B Products
Rate A]m B]n
Rate = k A]m B]n
Where k is the rate constant .
If A] = B] = 1 Mol L-1 than Rate = k
Thus rate constant is the rate of reaction when concentration of each reactant in the reaction is unity.
Consider a general zero order reaction
This method is applicable to those reactions wherein only one reactant is involved.
2.Initial rate Method:-
This method is used for those reactions where more than one reactant is involved.
In this method we carried out some series of experiments.
3.Integrated rate law Method:-
Most of the chemical reactions are accelerated by increase in temperature. For example, in decomposition of N2O5, the time taken for half of the original amount of material to decompose is 12 min at 50oC, 5 h at25oC and 10 days at 0oC. We also know that in a mixture of potassiumpermanganate (KMnO4) and oxalic acid (H2C2O4), potassium permanganate gets decolourised faster at a higher temperature than that at a lower temperature.
k = A e -Ea /RT1
2H2(g) + I2(g)→ 2HI(g)
ln k1 = – Ea/RT1 + ln A(2)
A + B →Products