1. Molarity :
Molarity ($M$) is defined as the number of moles of solute divided by the volume of the solution in liters ($L$). Mathematically, it is expressed as $M = \frac{{\text{{moles of solute}}}}{{\text{{volume of solution}}}}$.
When the temperature changes, the volume of a solution can change due to thermal expansion or contraction. As a result, the denominator in the molarity calculation, which represents the volume of the solution, can vary with temperature. This means that molarity can be affected by changes in temperature.
For example, if you have a solution with a certain number of moles of solute dissolved in a fixed volume of solvent, an increase in temperature may cause the solvent and solution volume to expand. As a result, the molarity will decrease because the volume in the denominator increases.
Conversely, if the temperature decreases, the solvent and solution volume may contract, leading to an increase in molarity as the volume in the denominator decreases.
2. Molality:
Molality ($m$) is defined as the number of moles of solute divided by the mass of the solvent in kilograms ($kg$). Mathematically, it is expressed as $m = \frac{{\text{{moles of solute}}}}{{\text{{mass of solvent}}}}$.
Molality is independent of temperature changes because it is based on the mass of the solvent rather than the volume. The mass of a substance typically remains constant with temperature changes unless there are specific physical or chemical processes occurring, such as evaporation or dissolution. Therefore, molality remains unchanged even when the temperature varies.
3. Mole fraction:
Mole fraction ($\chi$) is defined as the ratio of the number of moles of a component to the total number of moles in the mixture. Mathematically, it is expressed as $\chi = \frac{{\text{{moles of component}}}}{{\text{{total moles of all components}}}}$.
Mole fraction is not affected by temperature changes because it is a ratio and does not involve volume or mass terms. Regardless of the temperature, the number of moles of a component in a mixture and the total number of moles of all components remain the same. Therefore, the mole fraction remains constant irrespective of temperature variations.
4. Weight fraction :
Weight fraction ($w$) is defined as the ratio of the weight of a component to the total weight of the mixture. Mathematically, it is expressed as $w = \frac{{\text{{weight of component}}}}{{\text{{total weight of all components}}}}$.
Similar to mole fraction, weight fraction is also not influenced by temperature changes. Weight fraction is a ratio based on weight, which is typically independent of temperature variations (unless there are specific processes like evaporation or thermal decomposition occurring). Therefore, weight fraction remains constant regardless of temperature fluctuations.
In summary, molarity is the concentration factor that is affected by a change in temperature. Molality, mole fraction, and weight fraction are concentration measures that remain constant as they are not dependent on volume or mass terms affected by temperature. |
