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Pure liquids and solids are not included in the equilibrium equation. This is becasue they dont really have a concentration. On another note, please be aware that this doesn't mean water isnt included in the equilibrium equation. If a reaction involves water as a gas then it IS included in the equilibrium equation.
Kp is only used for gases, so you won't be able to use liquids or solids for that reaction. But for reactions with liquids, solids, and aqueous, then no, you do not include liquids or solids. This is because a pure substance does not really have a concentration and therefore does not affect the equation.
No they are not included in when solcing for Kc or Kp because and pure liquids don't have concentrations. Since solids and pure liquids aren't really mixed with other things, so that is why we can't really use them to calculate kc or kp. That is why it is ideal to use gases and aqueous solutions.
The only thing included is aqueous solutions and gases but not liquids or solids. You cannot have a concentration of a liquid and pure liquids do not really react much so that amount that existed in the reactants will almost be the exact same in the products which will just cancel out in the calculation of the equilibrium constant.
Solids and liquids are not used in equilibrium constants. Kc is used for concentrations while Kp is used for partial pressures. However, these can be converted between each other using the ideal gas law, PV=nRT.
Ana Pedreros wrote:If asked for the K expression, can Kc and Kp be used interchangeably?
I think the question will state clearly whether Kc or Kp is asked. If not, it will depend on the states of the substance involved in the reaction or the condition in the question.
if looking for Kp with concentration given, n/v, can be substituted for the concentration and the pressure can be isolated in order to find the partial pressure of that gas and compete the Kp expression.if looking for Kc with pressure given, p, can be inserted in the equation and n/v can be isolated in order to find the concentration of that gas and compete the Kc expression. R and T will stay the same depending on the given conditions.
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