Active mass, in the context of chemistry for Class 10, refers to the molar concentration of a substance (reactant or product) in a chemical reaction. In simpler terms, it's a measure of how much of a substance is 'actively' participating in the reaction within a given volume.
Understanding Active Mass
Active mass is crucial for understanding the rate of chemical reactions, particularly when applying the law of mass action. The law of mass action states that the rate of a chemical reaction is directly proportional to the active masses of the reacting substances.
- Definition: Active mass is essentially the number of moles of a substance present per unit volume.
- Relevance: It reflects the effective concentration of the reacting species and influences the reaction rate.
- Key Factors: Temperature and pressure can influence active mass, particularly for gaseous reactants/products.
Calculating Active Mass
The active mass can be calculated using the following formula:
Active Mass = (Number of moles) / (Volume in liters)
Often represented as:
Active Mass = n/V
Where:
n= number of moles of the substanceV= volume of the solution (or container) in liters (L)
Unit of Active Mass
The unit of active mass is moles per liter (mol/L) or moles per cubic decimeter (mol/dm3).
- mol/L: Indicates the number of moles of the substance present in one liter of the solution.
- mol/dm3: Since 1 liter is equal to 1 cubic decimeter, mol/dm3 is equivalent to mol/L.
Example
Suppose you have 2 moles of a reactant dissolved in 1 liter of solution.
Active Mass = 2 moles / 1 liter = 2 mol/L
Therefore, the active mass of the reactant in this solution is 2 mol/L.
