K = P^c _c middot [D]^d/[A]^a When calculating the equilibrium constant, aqueous
ID: 480017 • Letter: K
Question
K = P^c _c middot [D]^d/[A]^a When calculating the equilibrium constant, aqueous solutes must be expressed in moles per liter (M). and gases must be expressed in pressure as bars. This is because there are no other ways to express pressure or concentration other than bars or moles per liter (M). they are dimensionless ratios of the actual concentration or pressure divided by standard state concentration, which is 1 M for solutions and 1 bar for gases. these are the only units of concentration and pressure that are independent of temperature. the dimensionless ratios are always unity (1) because the concentration of the solute or pressure of the gas are divided by standard state concentrations. Pure solids and pure liquids are omitted from the equilibrium constant expression because the standard molar enthalpy of the formation of pure solids and pure liquids is zero. they are already in their standard states, so the ratio of the substance versus the standard state is unity (1). there is no way to express the concentration of a pure solid or liquid. pure solids and pure liquids do not participate in the equilibrium reaction.Explanation / Answer
Answer to the first question
they are dimensionless ratios of the actual concentration or pressure divided
by standard state concentration, which is 1 M for solutions and 1 bar for gases.
Answer to the second question
they are already in their standard states, so the ratio of the substance versus
the standard state is unity.
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