Conductance is the ease of current flow; conductivity is conductance per unit geometry.
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Conductance G is the reciprocal of resistance R, measured in siemens, and describes how easily current flows through a sample. Conductivity kappa is the conductance multiplied by the cell constant, the ratio of electrode separation to electrode area, and is measured in siemens per metre. It depends on the concentration, charge and mobility of the ions present, so it is a property of the solution rather than of the electrodes. Pure water has very low conductivity because it contains few ions. Conductivity measurements are used to monitor water purity and to study electrolyte solutions.
Key ideas: Conductance G = 1/R (siemens). Conductivity kappa = G x (l/A), where l/A is the cell constant in cm^-1, found by calibrating with 0.01 M KCl (kappa = 1.413 mS/cm at 25 C). Units: S/cm or S/m (1 S/cm = 100 S/m). Ultrapure water is 0.055 uS/cm; seawater about 50 mS/cm. Use AC to avoid electrolysis.
Common mistakes and connections: Mistakes: mixing cm and m units, confusing conductance with conductivity, and using DC, which polarizes electrodes. Conductivity of electrolytes rises with temperature (about 2 percent per degree), unlike metals. Measured conductivity is a quick proxy for total dissolved solids. Leads to molar conductivity.
Conductivity grows with the amount of dissolved ions, spanning about six orders of magnitude from ultrapure water to seawater. The interactive lesson shows this as a live animation or chart.
Seawater conducts electricity far better than rainwater because it contains much higher concentrations of dissolved ions.
Conductance is the ease of current flow; conductivity is conductance per unit geometry.
Conductance and Conductivity is a advanced topic in Acids, Bases & Electrochemistry. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Acids, Bases & Electrochemistry first: Prevention of Corrosion, Sacrificial Anode, Galvanization.
The next topics in Acids, Bases & Electrochemistry are Molar Conductivity and Kohlrausch's Law.
Yes. The interactive lesson includes a self-check question on Conductance and Conductivity, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Conductance and Conductivity is topic 80 of 105 in Acids, Bases & Electrochemistry.