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Mastering Chemical Kinetics (Chemistry for Class XII)
Somak Chatterjee|Mar 9th, 2014 07:39pm
Average rate:
- Rate of decrease in concentration of any one of the reactants
- Rate of increase in concentration of any one of the products
Instantaneous rate: The rate of a particular moment of time
Rate expression: The stoichiometric coefficients of reactants and products
Rate constant: The rate of reaction when the concentration of each of the reactant is taken as unity
Order of reaction: The sum of the exponents’ power of the concentration in the rate law
Molecularity of a reaction: Number of reacting species (atoms, ions or molecules) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction
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Feature |
Zero order reaction |
First order reaction |
Second order reaction |
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Order |
0 |
1 |
2 |
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Differential rate law |
d[R] /dt = −k
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d[R]/dt = −k[R]
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d[R]/dt = −k[R]
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Integrated Rate equation |
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Unit of rate constant |
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Mol-1s-1 |
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Graph |
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Half-life |
t1/2 = [R]0 / 2k |
t1/2 = 0.693 / k |
t1/2 =1/k[R]0 |
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Example |
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Pseudo first order reaction: These reactions depend on the concentration of only one reactant, when the concentration of other reactant is given in high concentration. Example: Hydrolysis of ethyl acetate
Factors affecting the rate of reaction:
1.Concentration- Generally rate of reaction increases when concentration gets increased.
2.Temperature- Increase in temperature increases the rate of reaction.
3.Catalyst-Catalyst increases the rate of reaction.
Arrhenius equation:
k = Ae–Ea/RT
Activation energy: Minimum energy required to start a chemical reaction. It is represented by Ea.
Questions asked in previous years:
Q. A reaction is of second order with respect to a reactant. How is its rate affected if the concentration of the reactant is (i) doubled (ii) reduced to half? (All India 2012 Set 3)
Q. Distinguish between ‘rate expression’ and ‘rate constant’ of a reaction. (All India 2011 Set 1)
Q. Nitrogen pentoxide decomposes according to equation: 2N2O5(g)à 4NO2(g) + O2(g)
This first order reaction was allowed to proceed at 40oC and the data below were collected:
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[N2O5] (M) |
Time (min) |
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0.400 |
0.00 |
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0.289 |
20.0 |
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0.209 |
40.0 |
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0.151 |
60.0 |
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0.109 |
80.0 |
(a)Calculate the rate constant. Include units with your answer.
(b)What will be the concentration of N2O5 after 100 minutes?
(c)Calculate the initial rate of reaction. (2011 Set 1)
Q. Define ‘rate of a reaction’. (Delhi 2010 Set 3)
Q. The rate constant for a reaction of zero order in A is 0.0030 mol L-1 s-1. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075M? (Delhi 2010 Set 3)
Q. A reaction is of first order in reactant A and of second order in reactant Β. How is the rate of this reaction affected when (i) the concentration of B alone is increased to three times (ii) the concentrations of A as well as B are doubled? (Delhi 2010 Set 3)
All the best,
Team Meritnation
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4. Abdul Qadeer Siddiqui | March 10th, 2014 at 3:39 pm
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7. PRIYANKA PALIWAL | March 8th, 2013 at 5:29 pm
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8. himanshu | March 8th, 2013 at 2:34 pm
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