What is kc in chemistry

Kp and Kc are equilibrium constants of ideal gas mixtures considered under reversible reactions. Kp is an equilibrium constant written with respect to the atmospheric pressure and the Kc is the equilibrium constant used with respect to the concentrations expressed in molarity.

So any time the number of gas molecules on the product side is the same as the number of gas molecules on the reactant side, Kc will be equal to Kp. The only thing which can change the value of Kc for a given reaction is a change in temperature. The position of equilibrium, however, can change without a change in the value of Kc. Changing the temperature is the only factor that changes the value of Kc for a given equilibrium.

Because there is an equal number of moles on both sides of the reaction, an increase in volume will have no effect on the equilibrium and thus there is no shift in the direction.

Similarly, when you decrease the volume there is no effect on the equilibrium. Equilibrium constants are not changed if you change the pressure of the system.

The only thing that changes an equilibrium constant is a change of temperature. That means that if you increase the pressure, the position of equilibrium will move in such a way as to decrease the pressure again — if that is possible. Equilibrium constants are changed if you change the temperature of the system. Kc or Kp are constant at constant temperature, but they vary as the temperature changes.

You can see that as the temperature increases, the value of Kp falls. The equilibrium constant does not change because it is a measure of the relative concentrations of the reactants and products at equilibrium.

As detailed in the above section, the position of equilibrium for a given reaction does not depend on the starting concentrations and so the value of the equilibrium constant is truly constant. It does, however, depend on the temperature of the reaction. The equilibrium constant is important because it gives us an idea of where the equilibrium lies. The larger the equilibrium constant, the further the equilibrium lies toward the products. Qc and Qp are the ratio of the concentrations or partial pressures of a system at a specific point at which the forward and reverse reactions are occurring.

It has not yet reached equilibrium, so it will be different from K. If Q is equivalent to K, then that "point" is equilibrium. K determines the ratio of product over reactant at equilibrium and the value should be the same for each reaction under the same conditions and temperature.

Q is very similar to K as they are calculated the same way with using products over reactants of the reaction. The exponents are the coefficients of the reactants and products from the equation. A typical esterification reaction is given below:. At room temperature, this value is approximately 4 for this reaction. It is helpful to write down the chemical equation for a equilibrium reaction whenever discussing an equilibrium constant, to ensure the expression is written correctly products over reactants.

An examples of a heterogeneous equilibrium is the equilibrium established if steam is in contact with red hot carbon. In this reaction, a gas reacts with a solid:. Another heterogeneous equilibrium involves shaking copper with silver nitrate solution; this reaction involves solids and aqueous ions:. The equilibrium constant expression is written the same way as in previous examples, omitting the solid carbon term:.

Both the copper on the left-hand side and the silver on the right are solids.