Chemical Equilibrium

Table of Contents

Introduction ……………………………………………………………………….. 3
Experimental Procedures ………………………………………………………….. 6
Results…………………………………………………………………………….... 9 Data Table 1: Serial Dilution and Spectrophotometer Practice……………..9
Data Table 2: SerialObservation of Le Chatelier’s Principle...……………..9
Data Table 3: Determination of Kc…………………………...…………….11
Calculations…………………………………………………………………12
Graphs..……………………………………………………………………...15
Pictures………………………………………………………………………16
Discussion…………………………………………………………………………...17
References…………………………………………………………………………...20

Introduction
In chemistry, a general idea applies that any chemical system that is not in equilibrium tends to behave in such ways that all its actions are towards reaching equilibrium. This idea also applies to a system already in equilibrium. Le Chatelier’s Principle states that if a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure due to a stress, then the equilibrium will shifts to counteract this change caused by the stress and a new equilibrium will be established (Graves/Thompson, 2012).
In regards to concentration, the equilibrium shift might result in a decrease in reactant concentration while the product concentration increases (right shift), or an increase in reactant concentration while the product concentration decreases (left shift) (Graves/Thompson, 2012). In terms of change of volume, a decrease in volume causes the reaction to shift in the direction of fewer moles of gas particles, and an increase in volume causes the reaction to shift in the direction of more moles of gas particles (Tro, 2008). When it comes to the effect of temperature change on equilibrium, it depends on whether the reaction is exothermic or endothermic. In an exothermic reaction, an increase in temperature causes the reaction to have a shift towards the left side and the value of the equilibrium constant (K) decreases, or if the temperature is decreases, the reaction has a shift to the right side and the value of the equilibrium constant increases (Tro, 2008). In an endothermic reaction, an increase in temperature causes the reaction to have a right shift and the equilibrium constant increases, or if the temperature is decreased, the value of the equilibrium constant decreases (Tro, 2008).
When representing a reaction at equilibrium, a double-headed arrow is used (Graves/Thompson, 2012). For instance, aA+bB Cc. In a reaction in equilibrium, the ratio of products to reactants is constant at a certain temperature (Graves/Thompson, 2012). The ratio is referred to as the equilibrium constant K: , where the letters A, B, and C within brackets represent the molarity (M) of a certain compound at equilibrium, and the exponents represent the stoichiometric coefficient of their respective compound in the chemical reaction equation (Graves/Thompson, 2012). To determine the value of , an “ICE” table is needed.

aA bB cC
I
(Initial)
0.5
0.5

0
C
(Concentration)
-ax
-bx

+cx
E
(Equilibrium)
0.5 - ax
0.5 - bx

cx
(Graves/Thompson, 2012)
In the initial concentration (I), there is a moment before the reaction takes place when the concentration of the product is zero (Graves/Thompson, 2012). For the change of concentration (C), a variable “x” can be used because the exact amount of A and B is unknown (Graves/Thompson, 2012). Since the reactants are expected to decrease, the variable “x” is subtracted from the initial concentration; for the concentration of the products, “x” is added to the initial concentration (Graves/Thompson, 2012). The ratio of “x” located in the (C) portion of the table is based on the stoichiometry of the reaction (Graves/Thompson, 2012).
In this experiment, students will be studying the reaction between iron (III) and thiocyanate to form a complex ion iron thiocyanate: (Graves/Thompson,