When writing an equilibrium constant expression, remember that products are on the top, and reactants are on the bottom of the expression. The coefficients for the compounds in the balanced reaction become the exponents for the compounds seen in the expression.

When Q = K, the reaction has reached equilibrium and is in a state of dynamic equilibrium, where the forward and reverse reactions are occurring at the same rate. Since there is no net change in concentration, the free energy is zero.

The only factor that changes the equilibrium constant is temperature. Changes in concentration of reactants or products by any means (whether addition, taking away solvent, or adding a chemical that will cause side reactions) will remove the system from equilibrium, but will not change the equilibrium constant.

For any equilibrium expression, solids and liquids are excluded because their concentrations are presumed to be constant during the reaction. The equilibrium expression is defined as the ratio of the concentration of products divided by the concentration of the reactants. Each reactant or product is raised to the power corresponding to its coefficient in the balanced chemical equation.

Using an arbitrary example:

Compare this to our question. Remember to exclude the solid magnesium!

This is one of the properties of the law of mass action. The equilbrium constant for a reaction written in reverse is 1/K.

The equilibrium constant is given by the concentraton of products over the concentration of reactants. If it lies to the right, it means that it favors the forward reaction, and thus the reaction is "more complete" or closer to completion.

This is one of the properties of the law of mass action—the concentrations of pure solids and liquids don't change over the course of the reaction.

Solids are not included in any equilibrium expression. The equilibrium expression will contain only aqueous solutions and gases. In addition, the coefficients of a balanced chemical equation correspond to exponents, not coefficients, in the equilibrium expression.

For this reaction, the only relevant product is oxygen gas and the only relevant reactant is fluorine gas.

All of the statements are properties of the law of mass action, except for the answer, which is a statement of Le Chatelier's Principle.

Given the equation delta G = -RTln(Keq), plugging in the correct values for the variables will lead us to the correct answer. Using e = 2.7, R = 8.314 J/molK, T= 298 K, and G = -4955 J, we can calculate that K = 7.4.