Question

A reaction follows the following concentration-time graph. The rate of this reaction at 20 seconds will be:

(A) $4 \times {10^{ - 3}}M{s^{ - 1}}$
(B) $2 \times {10^{ - 2}}M{s^{ - 1}}$
(C) $8 \times {10^{ - 2}}M{s^{ - 1}}$
(D) $7 \times {10^{ - 3}}M{s^{ - 1}}$

Answer 1

Hint:Reaction rate, in chemistry, the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time. Alternatively, it may be defined in terms of the amounts of the reactants consumed or products formed in a unit of time.

Complete step-by-step solution:(a) The rate of a reaction is usually observed by watching the disappearance of a reactant or the appearance of a product within a given time period.
(b) The concentration of C, $\left[ C \right]$ , is usually expressed in moles/liter. This is the average rate of appearance of product during the time interval $\Delta t$ . The limit of this average rate as the time interval becomes smaller is called the rate of appearance of product at time t, and it is the slope of the curve of $\left[ C \right]$ versus t at time t. This instantaneous slope, or rate, is written$\dfrac{{d\left[ C \right]}}{{dt}}$ .
(c) In the given graph slope is indicated by dotted line. And concentration from the graph = 0.35(likely) time=50 sec(likely)
So,$Rate\,of\,reaction = \dfrac{{concentration}}{{time}}$
$Rate\,of\,reaction(k) = \dfrac{{0.35}}{{50}}$ = $7 \times {10^{ - 3}}M{s^{ - 1}}$
(d) The rate of reaction remains constant for the whole time period of the reaction hence the rate of the reaction at time 20 second will be the same.

Hence the correct option is (D).

Note:Chemical reactions proceed at vastly different speeds depending on the nature of the reacting substances, the type of chemical transformation, the temperature, and other factors. In general, reactions in which atoms or ions (electrically charged particles) combine occur very rapidly, while those in which covalent bonds (bonds in which atoms share electrons) are broken are much slower. For a given reaction, the speed of the reaction will vary with the temperature, the pressure, and the amounts of reactants present. Reactions usually slow down as time goes on because of the depletion of the reactants. In some cases the addition of a substance that is not itself a reactant, called a catalyst, accelerates a reaction. The rate constant, or the specific rate constant, is the proportionality constant in the equation that expresses the relationship between the rate of a chemical reaction and the concentrations of the reacting substances. The measurement and interpretation of reactions constitute the branch of chemistry known as chemical kinetics.