Introducing equilibrium lab report

Lab #7- Equilibrium: A Model of Chemical Equilibria

• Determine the equilibrium expression for a chemical equation.
• Calculate the equilibrium constant for a chemical equation.
• Compare the numerical equilibrium constant and the relative amounts of reactants andproducts to evaluate an equilibrium expression. Introduction Equilibrium Most reactions begin by adding reactants to a reaction vessel. The reaction moves in the forward direction allowing products to be formed. Since there are no products present in the beginning, no products can collide and produce the original reactants. However, as the reaction progresses, eventually products are able to react to form reactants in the reverse reaction. An example of a reversible reaction is shown below. 𝑎𝐴+𝑏𝐵 ⇿ 𝑐𝐶+𝑑𝐷 At equilibrium the rate of the forward and reverse reaction is the same. In addition, the concentrations of each species in solution is essentially constant. Although none of these species may have the same concentration, they do not vary over time. Thus equilibrium is often called dynamic because allow at the macroscopic level no apparent changes are occurring, microscopically both the reverse and forward reactions are occurring simultaneously. Equilibrium can be reached from either a vessel initially containing all reactants (as the forward reaction allows for products to form) OR from a reaction vessel initially containing all products (as the reverse reaction allows the equilibrium concentrations of reactants to be reached. You will deal with both of these situations in this lab. Equilibrium Constant The equilibrium expression is a value that allows chemists to determine the extent of a reaction. The equilibrium expression is given by the equation 𝐾 = [𝐶]𝑐[𝐷]𝑑 [𝐴]𝑎[𝐵]𝑏 where the equilibrium constant K is equal to the concentration (in molarity) of products over reactants each raised to the exponent equal to the coefficient in the balanced equation. The equilibrium constant is the same for a reaction at the same temperature regardless of the initial concentrations of any species in solution. You will deal with four distinct reactions in this lab.

Values of Equilibrium Constant

The equilibrium constant can have a value ranging from nearly 0 to very high. A low K value indicates the reaction is reactant favored and will not proceed in the forward direction much. In contrast a K value that is very large will proceed nearly to completion and have high concentrations of products (in relation to reactants) present at equilibrium. A K value of ~1 indicates the reaction will proceed until the amounts of reactants and products present will be similar.