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Chemical Kinetics — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Kinetics4 Marks
Question
What is the relationship between coeffients of reactants in a balanced equation for an overall reaction and exponents in rate law. In what case the coeffients are the exponents?
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Answer

Explanation : Consider the following reaction, $aA + bB \rightarrow$ productsIf the rate of the reaction depends on the concentrations of the reactants A and B , then, by rate law,
$R \propto[A]^{a}[B]^{b}$
$\therefore R=k[A]^a\left[B^{b}\right.$
where $[A]=$ concentration of $A$ and
$[B]=$ concentration of $B$
The proportionality constant $k$ is called the velocity constant, rate constant or specific rate of the reaction.
a and b are the exponents or the powers of the concentrations of the reactants A and B respectively when observed experimentally.
The exponents or powers may not be necessarily a and b but may be different x and y depending on experimental observations. Then the rate $R$ will be,
$R=k[A]^x[B]^y$
For example, if $x=1$ and $y=2$, then,
$R=k[A] \times[B]^2$

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