Chapter 4 Chemical Kinetics Solutions
Question - 1 : - For the reaction R—>P, the concentration of reactant changes from 0.03 M to 0.02 M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.
Answer - 1 : -
Average rate of reaction _13-11-08_Utpal_12_Chemistry_4_9_html_7c1ba064.gif)
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= 6.67 × 10_−6 M s_−1
_
For the reaction R → P,the concentration of a reactant changes from 0.03 M to 0.02 M in 25 minutes.Calculate the average rate of reaction using units of time both in minutes andseconds.
Answer - 2 : - Average rate of reaction 
Question - 3 : - In a reaction, 2A → Products, the concentration of A decreasesfrom 0.5 mol L−1 to0.4 mol L−1 in 10 minutes. Calculate the rate duringthis interval?
Answer - 3 : - Average rate 
= 0.005 mol L−1 min−1
= 5 × 10−3 M min−1
. What is the order of the reaction?
Answer - 4 : - The order of the reaction
Question - 5 : - The conversion of molecules X toY follows second order kinetics. If concentration of X is increased to threetimes how will it affect the rate of formation of Y?
Answer - 5 : -
The reaction X → Y follows secondorder kinetics.
Therefore,the rate equation for this reaction will be:
Rate = k[X]2 (1)
Let [X] = a mol L−1,then equation (1) can be written as:
Rate1 = k .(a)2
= ka2
If theconcentration of X is increased to three times, then [X] = 3a mol L−1
Now, therate equation will be:
Rate = k (3a)2
= 9(ka2)
Hence,the rate of formation will increase by 9 times.
Question - 6 : - A first order reaction has a rateconstant 1.15 10−3 s−1. How long will 5 g of this reactant take toreduce to 3 g?
Answer - 6 : -
From the question, we can write down the following information:
Initialamount = 5 g
Finalconcentration = 3 g
Rate constant = 1.15 10−3 s−1
We know that for a 1st orderreaction,
= 444.38 s
= 444 s(approx)
Question - 7 : - Time required to decompose SO2Cl2 to half of its initial amount is 60minutes. If the decomposition is a first order reaction, calculate the rateconstant of the reaction.
Answer - 7 : -
We know that for a 1st orderreaction,
It is given that t1/2 = 60 min
Question - 8 : - What will be the effect oftemperature on rate constant?
Answer - 8 : -
The rate constant of a reaction is nearly doubled with a 10° risein temperature. However, the exact dependence of the rate of a chemicalreaction on temperature is given by Arrhenius equation,
Where,
A is the Arrhenius factoror the frequency factor
T is the temperature
R is the gas constant
Ea is the activation energy
Question - 9 : - The rate of the chemical reactiondoubles for an increase of 10 K in absolute temperature from 298 K. Calculate Ea.
Answer - 9 : -
It is given that T1 = 298 K
∴T2 =(298 + 10) K
= 308 K
We alsoknow that the rate of the reaction doubles when temperature is increased by10°.
Therefore,let us take the value of k1 = k and that of k2 = 2k
Also, R = 8.314 J K−1 mol−1
Now,substituting these values in the equation:
We get:
= 52897.78 J mol−1
=52.9 kJ mol−1
Question - 10 : - The activation energy for thereaction
Answer - 10 : -
2HI(g) → H2 + I2(g)
is 209.5 kJ mol−1 at 581K. Calculate the fraction ofmolecules of reactants having energy equal to or greater than activation energy?
Answer
the given case:
Ea = 209.5 kJ mol−1 = 209500 J mol−1
T = 581 K
R = 8.314 JK−1 mol−1
Now, the fraction of molecules of reactantshaving energy equal to or greater than activation energy is given as:
