How does temperature affect molar conductivity and why does specific conductance decrease and equivalent conductance increases with dilution of a solution of electrolyte?
I'll address the effects of temperature and dilution on different conductivity measures for electrolyte solutions:
Temperature:
- Molar conductivity (Λm): Increases with increasing temperature. The higher kinetic energy of ions due to increased thermal motion leads to greater mobility and thus, higher conductivity.
- Specific conductance (κ): Increases with increasing temperature for the same reason as molar conductivity.
Dilution:
- Molar conductivity (Λm): Increases with dilution. As the solution becomes less concentrated, the distance between ions increases, reducing interionic attractions and allowing them to move more freely, enhancing conductivity. This effect is more pronounced for weak electrolytes due to increased dissociation upon dilution.
- Specific conductance (κ): Decreases with dilution. While the total number of ions remains constant upon dilution, the number of ions per unit volume (concentration) decreases. This directly reduces the specific conductance, which measures the ability of the solution to conduct electricity per unit volume.
- Equivalent conductance (Λe): Increases with dilution. Even though the number of ions per unit volume decreases, the total number of ions and the volume increase proportionally. The definition of equivalent conductance accounts for this, leading to an increase with dilution for similar reasons as molar conductivity.
Summary:
MeasurementEffect of TemperatureEffect of DilutionMolar conductivity (Λm)IncreasesIncreasesSpecific conductance (κ)IncreasesDecreasesEquivalent conductance (Λe)No significant effectIncreases
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Molar conductivity is defined as the conducting power of all the ions produced by dissolving one mole of an electrolyte in solution. With increase in the temperature, the molar conductivity of an electrolyte increases with increase in the interaction of the ions. As temperature increases, the molar conductivity also increases. Conductivity of metal decreases with temperature while conductivity of electrolytic conductors increases with temperature. Due to the increase in dilution, the equivalent conductance increases and at infinite dilution, the value of equivalent conductance is highest and it is termed as equivalent conductance at infinite dilution. Therefore, the equivalent conductance for strong electrolyte on dilution increases. The equivalent conductance of strong electrolyte is increased by dilution, because its value is equal to the multiple of Kv and the volume of solution. By making dilution the volume of solution increases which also increase the value of equivalent conductivity. The dissociation of a weak electrolyte and strong electrolyte increases with dilution giving more ions, its molar conductance increases with dilution. The solution of weak and strong electrolyte is diluted, the volume of the solution increases, hence equivalent conductivity increases.The conductance of solution increases on dilution. The specific conductivity decreases on dilution. The equivalent conductivity and molar conductivity increases with dilution. The equivalent and molar conductivities tend to accumulate maximum value with increasing dilution. The molar conductance of a solution increases with dilution, while its specific conductance decreases with dilution. When solution is diluted, the total number of ions increases due to increase in the degree of dissociation. Hence, molar conductance increases with dilution.Temperature affects the degree to which an electrolyte gets dissolved in a solution. It has been seen that higher temperature enhances the solubility of electrolytes and hence the concentration of ions which results in increased electrolytic conduction.
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