Rate of a reaction decreases with the passage of time as the concentration of reactants decrease. Conversely, rates generally increase when reactant concentrations increase. So, rate of a reaction depends upon the concentration of reactants.
Consider a general reaction
aA + bB → cC + dD
where a, b, c and d are the stoichiometric coefficients of reactants and products.
The rate expression for this reaction is
Rate ∝ [A]x [B]y
where exponents x and y may or may not be equal to the stoichiometric coefficients (a and b) of the reactants.
Above equation can also be written as Rate = k [A]x [B]y
-\(\frac{dR}{dT}\) = k [A]x [B]y
This form of equation is known as differential rate equation, where k is a proportionality constant called rate constant.
In the reaction A + 3B → 2C + D. Which of the following expression does not describe changes in the concentration of the various species as a function of time?
Answer & explanation
Correct answer: option 2
In the reaction A + 3B → 2C + D
rate = -\(\frac{d[A]}{dT}\) = -\(\frac{1}{3}\)\(\frac{d[B]}{dT}\) = +\(\frac{1}{2}\)\(\frac{d[C]}{dT}\) = +\(\frac{d[D]}{dT}\)
-\(\frac{1}{3}\)\(\frac{d[B]}{dT}\) = +\(\frac{1}{2}\)\(\frac{d[C]}{dT}\)
\(\frac{d[B]}{dT}\) = -\(\frac{3}{2}\)\(\frac{d[C]}{dT}\)