$A+B \rightleftharpoons C$
The unit of the thermodynamic equilibrium constant for the reaction is
Units of Thermodynamic Equilibrium Constant Explained
The thermodynamic equilibrium constant ($K$) for a reaction is defined using the activities of the reactants and products, not their concentrations or partial pressures directly.
Thermodynamic Equilibrium Constant ($K$)
Consider the reversible reaction: $A + B \rightleftharpoons C$
The thermodynamic equilibrium constant ($K$) is expressed as the ratio of the activities of the products to the activities of the reactants, each raised to the power of their stoichiometric coefficients:
$K = \frac{a_C}{a_A \cdot a_B}$Here, '$a$' denotes activity.
Activity Definition
Activity is a dimensionless quantity. It represents the effective concentration (or pressure) of a species relative to a standard state. For a species '$i$' in solution, its activity ($a_i$) is defined as:
$a_i = \frac{[i]}{[i]^0}$Where:
- $[i]$ is the molar concentration of species $i$.
- $[i]^0$ is the standard state concentration, typically taken as 1 mol $L^{-1}$.
Since the activity is a ratio of concentration to a standard concentration (or pressure to a standard pressure), the units cancel out, making activity dimensionless.
Conclusion on Units of $K$
As $K$ is calculated as the ratio of dimensionless activities ($a_C$, $a_A$, $a_B$), the overall value of $K$ is also dimensionless.
Therefore, the correct unit for the thermodynamic equilibrium constant is dimensionless.
Important Questions from Chemical Equilibrium
- The molar extinction coefficient of proline ninhydrin complex at 520 nm is 0.34 $\mu$M$^{-1}$Cm$^{-1}$. A solution of the proline ninhydrin complex has an absorbance of 0.68 in a one centimeter cuvette. The concentration ($\mu$M) of proline is
- The amount of a particular gas dissolved in water depends on
(i) its solubility in water.
(ii) its partial pressure at the air/water interface or sediment/water interface.
(iii) the water temperature.
(iv) the levels of salts in the water.
Identify the correct answer : - A 50 ml solution of pH = 1 is mixed with a 50 ml solution of pH = 2. The pH of the mixture will be nearly
- The solubility product of the following type of reaction :
$Al(OH)_3 \rightarrow Al^{3+} + 3\bar{O}H$ is Consider the reaction $2C(s) + O_2(g) \rightleftharpoons 2CO(g)$ at equilibrium.
The equilibrium can be shifted towards the forward direction by
