Chapter 13 Part 2 PDF

Chapter 13 Part 2 CHEM 0120  Calculating Equilibrium Concentrations Steps to follow when solving for equilibrium concentrations: 1) Set up an ICE table with expressions in x Initial concentration or Starting concentration Change in concentration to reach equilibrium...

Chapter 13 Part 2 CHEM 0120  Calculating Equilibrium Concentrations Steps to follow when solving for equilibrium concentrations: 1) Set up an ICE table with expressions in x Initial concentration or Starting concentration Change in concentration to reach equilibrium Equilibrium concentration 2) Substitute the expressions in x for equilibrium concentrations into the equilibrium-constant equation. 3) Solve the equilibrium-constant equation for the values of the equilibrium concentrations. 2  Change in Reaction Conditions Ways to alter the equilibrium composition of a gaseous reaction mixture: 1) Change the concentrations by adding reactants to the reaction vessel or by removing products from the reaction vessel. 2) Change the partial pressure of gaseous substances by changing the volume. 3) Change the temperature. 3 Removing Products or Adding Reactants Apply Le Chatelier’s principle When a system in chemical equilibrium is disturbed by a change of temperature, pressure, or a concentration, the system shifts in equilibrium composition in a way that tends to counteract this change of variable. Example: CO g + 3H2 g ⇌ CH4 g + H2 O(g) At the new equilibrium position, the concentrations of reactants and products will be such that the value of the equilibrium constant is the same. 4  Effect of Concentration Changes on Equilibria The net reaction occurs left to right (the reaction occurs in the forward direction) to give a new equilibrium when reactant is added or product is removed from an equilibrium mixture. More products are produced. The net reaction occurs right to left (reverse direction) to give a new equilibrium when more product is added or reactant is removed from an equilibrium mixture. More reactants are produced. 5  Effect of Pressure Change If the volume of the container is decreased, the concentration of the gases increases. Partial pressure of the gases increases, which causes an increase of the total pressure in the container. According to Le Chatelier’s principle, the equilibrium will shift to remove that pressure. If the pressure is increased by decreasing the volume of a reaction mixture, the equilibrium shifts to the side with fewer gas molecules. 6 Chemical equilibrium change with pressure change CO g + 3H2 g ⇌ CH4 g + H2 O(g) Comparison of gases: 1) At equilibrium (consider the amounts in the earlier example) 2) After compression 3) Compressed and at equilibrium (shifts equilibrium to the right) 7  Effect of Temperature: Endothermic Endothermic reactions absorb energy. Heat is “behaving” as a reactant. In an endothermic chemical reaction, heat is a reactant. Increasing the temperature causes an endothermic reaction to shift right (in the direction of the products); the equilibrium constant increases. Decreasing the temperature causes an endothermic reaction to shift left (in the direction of the reactants); the equilibrium constant decreases. 8  Effect of Temperature: Exothermic Exothermic reactions release energy. Heat is “acting” as a product. In an exothermic chemical reaction, heat is a product. Increasing the temperature causes an exothermic reaction to shift left (in the direction of the reactants); the value of the equilibrium constant decreases. Decreasing the temperature causes an exothermic reaction to shift right (in the direction of the products); the value of the equilibrium constant increases. 9