Pure substances
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Pure substances
Hi! What does it mean by solids and liquids being pure substances? And why don't the concentrations of pure substances change in a reaction?
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Re: Pure substances
Hi! I think the meaning behind solids and liquids being pure substances is that they do not interact with the other aqueous and gaseous solutions in the chemical reaction, and this is why their concentration do not change (or at least do not change enough to be considered).
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Re: Pure substances
Pure substances cannot have a concentration because there is only one substance present. In order for something to have a concentration, there must be a solute and a solvent. It is like trying to say how concentrated or dilute a glass of water is. Since the concentrations of pure substances do not exist and cannot change, they do not contribute to the expression for K.
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Re: Pure substances
For liquids, their concentrations don't change because they are in so much excess that the change is very minimal in comparison to their concentrations. When we write the expression for k, since their concentrations don't change on the reactant and product side, they would cancel out in the numerator and denominator, which is why we don't include them when solving for k. Solids also don't have concentrations since concentration is in moles/liter of solution and if something is a solid, it hasn't been in the solution yet so therefore their concentrations can't be taken into account anyways.
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Re: Pure substances
The molar concentration of pure substances does not change in a reaction. Because solids and liquids are considered pure substances, they are not included in the equilibrium constant expression.
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Re: Pure substances
The concentrations of pure substances (solids and liquids) are not involved in the calculation of the equilibrium constant, K, of chemical reactions because the change in their concentrations is so small, it is negligible. For example, if you have $1 million and you lose $1, you would still say that you have $1 million rather than $999,999. Since the change in concentrations of liquids is so small, it is insignificant, which is why you would omit it in the expression for K.
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Re: Pure substances
Hi, I think it is because the molar concentration of a solid or liquid can not change very easily. For example, water is usually in great excess, and a chemical compound that is solid doesn't change its concentration when it is still in its solid form. So the change in concentration for pure substance is minor and can be omitted.
Re: Pure substances
The concentrations do not change because solids are in mol, while the reaction needs molL^-1. Liquid such as water is present on both sides and cancels out when calculating the K value.
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Re: Pure substances
For pure solid and pure liquid, active mass is taken to be unity, i.e., 1 as they remain constant throughout the reaction. In other words, pure liquids and solids are made up of one substance, hence they do not have a concentration because it doesn't change enough.
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Re: Pure substances
In equilibrium reactions, there’s so much of these pure substances that their concentration doesn’t really change.
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