Question

Define reaction quotient.

Answer 1

You can start by describing thermodynamics in brief. Then move on to describe what activity of a chemical species is, as it is very essential to describe what reaction quotient is. Finally define reaction quotient and also given an example of a general chemical reaction and find out its reaction quotient. Also define the relation between reaction quotient and equilibrium constant.

Complete step by step solution:

The concept reaction quotient comes under the study of thermodynamics in chemistry.
Thermodynamic is a branch of science that in respect to chemistry gives us the relation of work and heat in chemical reactions. In even simpler terms it deals with the study of the process of conversion of energy between different forms of energy. Thermodynamics is a very important concept as it helps us to improve the efficiency of our equipment to save energy and produce less heat (wasted energy).
To understand what reaction quotient means in an easy manner, we need to understand what activity of the product and reactant means. Thermodynamic activity (symbol $a$) is a measure of the effective concentration of a species in a mixture.
Reaction quotient – The reaction quotient is a quantity that establishes a relation between quantity of products and quantity of reactants, for a certain point in time. Reaction quotient is best defined by the ratio of molar concentration (or activities) of the products to that of the reactants.
Let’s imagine a general chemical reaction. Here $\alpha$ moles of a reactant A reacts with $\beta$ moles of reactant B, and produces $\gamma$ moles of product C and $\delta$ moles of product D. The reaction is shown below
- The reaction is written as an equilibrium even though it may appear in many cases that all the reactants on one side have been converted to the other.
- The reaction quotient ${Q_r}$, written as a function of time is
${Q_r}(t) = \dfrac{{\\{ R\\} _t^\gamma \\{ S\\} _t^\delta }}{{\\{ A\\} _t^\alpha \\{ B\\} _t^\beta }}$
- For the condition of equilibrium, we know that equilibrium constant is
${K_{eq}} = \dfrac{{\\{ R\\} _t^\gamma \\{ S\\} _t^\delta }}{{\\{ A\\} _t^\alpha \\{ B\\} _t^\beta }}$
- So for the condition of equilibrium
${K_{eq}} = \dfrac{{\\{ R\\} _t^\gamma \\{ S\\} _t^\delta }}{{\\{ A\\} _t^\alpha \\{ B\\} _t^\beta }} = {Q_r}(t)$

Note: Reaction quotient is a measure of the direction in which our reaction will proceed. For an ideal reaction, in the starting of reaction we have no products so ${Q_r}$becomes zero (${Q_r}$is less than${K_{eq}}$), in the case of equilibrium ${Q_r} = 1$(${Q_r}$ is equal to ${K_{eq}}$) and in the end we will have no reactant left so ${Q_r}$ will become infinity (${Q_r}$ is greater than ${K_{eq}}$).