Question

Define reaction quotient (Q).

Answer 1

Hint :Reaction quotient is the ratio of the concentration of the products and reactant in a reversible reaction. For equilibrium reaction it is equal to the equilibrium constant. It may be greater than 1 or less than depending on the concentration of products and reactant.

Complete Step By Step Answer:
In thermodynamics, the reaction quotient (Q) is a quantity that is the ratio of the concentration of the products and reactant in a reversible reaction. For equilibrium reaction it is equal to the equilibrium constant.
Let us take that,
For reversible reaction $ A + B \rightleftarrows C + D $
where a, b, c, are the stoichiometric coefficients for the balanced reaction, we can calculate Q using the following equation which is as follows:
 $ Q = \dfrac{{{{\left[ C \right]}^c}{{\left[ D \right]}^d}}}{{{{\left[ A \right]}^a}{{\left[ B \right]}^b}}} $
Now according to the LeChatelier’s principle, we know that when a pressure is applied that affects a reaction away from equilibrium, the reaction will try to adjust to get back to equilibrium.
The reaction quotient Q is a measure of the relative concentration of product and reactants in irreversible reactions.
Additional information:
 The reaction quotient Q becomes equal to equilibrium constant K when equilibrium is achieved. Unlike K, which is based on equilibrium concentrations of a reaction, Q can be calculated whether we are at equilibrium or not.
The magnitude of reaction quotient denotes the relative concentration of product and reactants in reaction vessels.
If K > Q, then a reaction will move in forward direction, converting reactants into products.
If K < Q, the reaction will move in the reverse direction, converting products into reactants.
If Q = K, then the system is at equilibrium, the rate of conversion is zero.

Note :
It is important for students to be able to understand the concepts involved in Le Châtelier’s. Otherwise it would not be possible for them to be able solve the given question. Gibbs energy is also an important factor to determine the spontaneity of a reaction.