Write an equilibrium expression for each chemical equation involving one or more solid or liquid reactants or products. a. CO3 2-(aq) + H2O(I)HCO3 -(aq) + OH-(aq) b. 2 KCIO3(s)2 KCI(s) + 3 O2(g) c. HF(aq) + H2O(I)H3O+(aq) + F-(aq) d. NH3(aq) + H2O(I)NH4 +(aq) + OH-(aq)

Understanding the concept of chemical equilibrium is crucial when looking at reactions that can occur in both the forward and reverse directions. At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, leading to a state where the concentrations of reactants and products remain constant over time, although they are not necessarily equal.

Chemical equilibrium does not imply that reactants and products are in equal concentration, but rather that their concentrations have stabilized in a ratio that will remain unchanged without outside influence. It's also important to note that the reaction has not stopped at this point; reactants and products are continually being formed, but at a rate that does not yield a net change in concentration.

When writing equilibrium expressions, we must consider the physical states of the reactants and products. In an equilibrium expression, we only include the species that are in the aqueous (aqueous solutions, denoted by 'aq') or gaseous (denoted by 'g') state.

This is because the concentrations of solids and liquids remain relatively constant throughout the reaction and do not affect the equilibrium position of a chemical system. Concentrations of substances in the aqueous and gaseous phases, on the other hand, do change and can shift the equilibrium when altered, making it essential to include them in our calculations.

We use the concentration [ ] for species in solution and partial pressures (P) for those in the gaseous state to express their amounts at equilibrium.

Le Chatelier's principle explains how a system at equilibrium will respond to a change in conditions. If an external stress—such as a change in concentration, pressure, or temperature—is applied to a system, the equilibrium will shift to counteract the stress and establish a new equilibrium state.

For example, if we increase the concentration of a reactant, the system reacts by shifting the equilibrium to the right to produce more products. Conversely, removing a product from the system will result in the equilibrium shifting to the right to produce more product and restore balance.

The equilibrium constant is a value that expresses the ratio of the concentrations of products to reactants at chemical equilibrium. Depending on the phases of the reactants and products, we use different types of equilibrium constants. For reactions involving species in solution, we use Kc, which is based on the concentrations of the reactants and products.

On the other hand, when dealing with gaseous species, we often use Kp, which relates to the partial pressures of gases involved in the reaction. Despite being calculated differently, Kc and Kp are related and can be converted from one to the other for the same reaction at a given temperature using the ideal gas law equation. It is crucial to remember that solid and liquid phases are not included in these calculations as their concentrations do not change during the reaction.