Question

In the reaction $ 2A+B\to 2C+D\text{ },\text{ }5\text{ }mol/lt $ of 'A' is allowed to react with $ 3\text{ }mol/lt $ of B. After $ 5 $ seconds the concentration of A was found to be $ 4 $ molar. What is the rate of reaction in terms of A?
(A) $ 0.1M/\sec . $
(B) $ 0.2M/\sec . $
(C) $ 0.3M/\sec . $
(D) $ 0.15M/\sec . $

Answer 1

Hint: We know that the rate of the reaction is dependent on concentration. The rate of a reaction is the speed at which the chemical reaction takes place. Here we have to know the rate or speed at which the chemical reaction is happening i.e. the reactant is getting converted into a product.

Complete step by step solution:
So in the question it is asked how we will find the rate of reaction, it's quite a vague question. We are familiar with the word rate which usually refers to speed. Here the question is about the rate of reaction i.e. the speed of the chemical reaction. We know that in a chemical reaction a reactant is undergoing the change under suitable reaction conditions and finally yields the products here we have to know the rate or speed at which the chemical reaction is happening i.e. the reactant is getting converted into a product.
From this statement we could have an idea that so everything that rate is dependent is on the concentration terms of the reactants or the concentration of the products. Thereby we can conclude that we could measure the rate of reaction if we observe the concentration terms and the time taken. The chemical reaction here we have is: $ 2A+B\to 2C+D $ i.e.
 $ 5M(2A)+3M(B) $ Initial concentration, and $ 4M $ is $ t=5\sec . $
Thus, $ Rate\text{ }of\text{ }reaction\text{ }in\text{ }terms\text{ }of\text{ }A\text{ }=\text{ }\dfrac{Change\text{ }in\text{ }concentration.}{Change\text{ }in\text{ }Time.}=\dfrac{5-4}{5-0}=0.2M/\sec $
Therefore, the correct answer is option B.

Note:
Remember that if in a reaction equation coefficients are involved then we will divide the rate of the formation of diminishing of the species with respect to the coefficient term for those species. Coefficients are those numerical digits that are inserted in a chemical equation to get a balanced equation.