Question

What is the difference between q and k in equilibrium?

Answer 1

"Q" in equilibrium	“K” in equilibrium
The reaction constant or reaction quotient is denoted by the letter “Q” in any equilibrium reaction.	The equilibrium constant is denoted by the letter “K” in any equilibrium reaction.
The reaction quotient is defined as the ratio of the concentrations of product to the concentration of reactants.	The equilibrium constant is defined as the ratio of the concentrations of product to the concentration of reactants at equilibrium under standard conditions.
The reaction quotient is applied or calculated at any point or time of the reaction i.e. before it reaches equilibrium or after equilibrium is achieved.	The equilibrium constant is calculated when the reaction reaches equilibrium or the reactions are at equilibrium.
The reaction quotient gives us an idea of the further proceeding of the reaction which means either in the forward direction or in the backward direction.	The equilibrium constant does not give any idea about the reaction.
As the reaction proceeds the value of the reaction quotient changes from time to time.	With the change in time, no change can be observed in the value of the equilibrium constant.
Example: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\to 2{\mathrm{NH}}_3\left(\mathrm{g}\right)$ Calculation of reaction quotient:${\mathrm{Q}}_{\mathrm{c}}=\frac{{\left[{\mathrm{NH}}_3\right]}^2}{\left[{\mathrm{N}}_2\right]{\left[{\mathrm{H}}_2\right]}^3}$	Example: ${\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{HCO}}_3^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$ Calculation of equilibrium constant: $\mathrm{K}=\frac{\left[{\mathrm{HCO}}_3^{-}\right]\left[{\mathrm{H}}^{+}\right]}{\left[{\mathrm{H}}_2{\mathrm{CO}}_3\right]}$

• Q can be used to determine which direction a reaction will shift to reach equilibrium.
• If K > Q, a reaction will proceed forward, converting reactants into products.
• If K < Q, the reaction will proceed in the reverse direction, converting products into reactants.
• If Q = K then the system is already at equilibrium.