Which of the following concentration factor is affected by change in temperature? (a) Molarity (b) Molality (c) Mole fraction (d) Weight fraction

Molarity is a fundamental concept in chemistry that helps us describe the concentration of a solution. It is defined as the number of moles of solute present in one liter of solution. Mathematically, it can be expressed using the formula:
\[ Molarity (M) = \frac{moles \, of \, solute}{liters \, of \, solution} \]
Molarity is temperature-dependent because the volume of a solution can change with the temperature due to thermal expansion or contraction. As temperature increases, the volume of a liquid tends to increase, which may result in a lower concentration of the solute if the number of moles remains constant. This is important to consider in chemical reactions where consistent molarity is required. For practical applications, chemists often measure and report concentrations at a standard temperature to maintain consistency.

Molality is another way to express the concentration of a solution, especially useful when temperature fluctuates. It is defined as the number of moles of solute per kilogram of the solvent. Unlike molarity, molality does not change with temperature because it is based on mass, which is not affected by temperature changes. The formula for molality is given by:
\[ Molality (m) = \frac{moles \, of \, solute}{kilograms \, of \, solvent} \]
Due to its temperature independence, molality is particularly valuable for studying properties of solutions under varying thermal conditions, such as in boiling point elevation and freezing point depression experiments.

The mole fraction is a dimensionless quantity representing the ratio of the number of moles of one component to the total number of moles of all components in the mixture. It provides a way to express the concentration of a constituent in a mixture without using units. The mole fraction, represented by \( \chi \), is calculated as follows:
\[ Mole \ Fraction (\chi) = \frac{moles \, of \, component}{total \, moles \, of \, all \, components} \]
Because the mole fraction is a ratio, it remains unaffected by temperature changes. Such constancy makes mole fraction ideal for applications that involve different phases of matter or those that operate over a wide range of temperatures, such as gas mixtures.

Understanding the temperature dependence of various concentration terms is vital when working with chemical solutions. As established, molarity is susceptible to temperature changes because it is dependent on the volume, which can expand or contract with the temperature fluctuations. Conversely, molality and mole fraction are not influenced by temperature as they are ratios that are independent of volume.
This distinction is crucial when choosing the right concentration measure for an experiment or industrial process. For example, in endothermic and exothermic reactions where heat is absorbed or released, choosing a temperature-independent concentration like molality or mole fraction is advantageous for maintaining accurate and consistent readings despite the thermal changes occurring during the reaction.