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Hi! So basically (aq) stands for aqueous which basically means the substance is dissolved in water. (l) stands for liquid and that means the substance is in it's pure liquid state. We don't include H20 when calculating the equilibrium constant because it's a pure substance. The molar concentration of a PURE substance (a solid or a liquid) does not change in a reaction, so solids and liquids are not included in the equilibrium constant. We're only focused on things when considering equilibrium constants that are in concentration terms and change through the process of the reaction. A pure liquid does not change. Typically, water involved in a reaction is in such large excess that the concentration of water is essentially constant because very little is being used. Therefore, having water in the numerator and the denominator of the equilibrium constant would cause them to cancel. So, we just don't include it, as water is a pure substance. Hope this helps!
Aq means aqueous which indicates a solute dissolved in water. Aqueous substances are included in the equilibrium constant equation. l means liquid (a pure liquid) which is not included in the equilibrium constant since they don't have a concentration so there is no change in concentration. We only exclude H2O in the equilibrium constant when it is a liquid since it is a solvent and its concentration doesn't change from reactant to product. If H2O is a gas, then it is included in the equilibrium constant.
Aqueous(aq) is when you dissolve something into water to form a solution. For example, if you dissolve NaCl into water, you will get NaCl(aq). In contrast, liquid(l) simply means that a substance is in a purely liquid state. For example, H20(l) and C2H5OH(aq), which correspond to liquid water and liquid ethanol.
We don't include water because it is available in such a large amount that very little is being put to use. Therefore, it is considered a constant and allows for water to be canceled out in the equation.
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