activity coefficient

activity coefficient
Number expressing the ratio of a substance's chemical activity to its molar concentration (see mole).

The measured concentration of a substance may not be an accurate indicator of its chemical effectiveness as represented by the equation for a particular reaction; in such cases, the activity is calculated by multiplying the concentration by the activity coefficient. In solutions, the activity coefficient is a measure of how much the solution differs from an ideal solution.

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      in chemistry, the ratio of the chemical activity of any substance to its molar concentration. The measured concentration of a substance may not be an accurate indicator of its chemical effectiveness, as represented by the equation for a particular reaction, in which case an activity coefficient is arbitrarily established and used instead of the concentration in calculations. In solutions, the activity coefficient is a measure of how much a solution differs from an ideal solution—i.e., one in which the effectiveness of each molecule is equal to its theoretical effectiveness.

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Universalium. 2010.

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