Recognizing Equilibrium Section 7 1 Equilibrium Systems All

Recognizing Equilibrium Section 7. 1

Equilibrium Systems • All of the reactions we have focused on in this course have gone to completion, however there are some reactions that do not proceed to completion. • Consider the following reaction: 2 NO 2(g) N 2 O 4(g) Brown a) Initially the vial contains only molecules of brown nitrogen dioxide gas. b) Some of the nitrogen dioxide gas has been converted to dinitrogen tetroxide gas which is colourless Colourless c) & d) an equilibrium is established, so the gas remains the same colour.

Equilibrium Condition • Equilibrium • occurs when opposing changes to a closed chemical system occur simultaneously at the same rate Swimming Pool Banking Bus

Dynamic Equilibrium • A balance between forward and reverse processes that are occurring simultaneously Consider the following reaction: H 2 O(g) + CO(g) H 2(g) + CO 2(g) The concentration of product increases over time and the concentration of reactant decreases over time. Eventually the concentrations of the reactant and product remain stable. This is the point at which chemical equilibrium has been reached.

Equilibrium position • the relative concentrations of reactant and products in a system in dynamic equilibrium Reversible reactions • a chemical reaction that proceeds in both the forward and reverse directions, setting up an equilibrium in a closed system. Ø Reverse reactions are identified by a double arrow. Ø An equilibrium position can be reached starting from the forward reaction or from the reverse reaction.

Conditions that Apply to all Equilibrium Systems ü achieved in reversible process when the rates of opposing changes are equal ü observable (macroscopic) properties of a system at equilibrium are constant ü can be approached from either direction ü can only be reached in a closed system

Determining Concentrations For Chemical Equilibria o You can predict the changes in concentration of reactants and products as a system approaches equilibrium from the coefficients of a balanced chemical equation. Consider the following equation: N 2(g) + 3 H 2(g) � 2 NH 3(g) o The molar ratio is 1: 3: 2. This means that the decrease in hydrogen gas concentration is 3 times the decrease in nitrogen gas concentration. The increase in ammonia concentration is 2 times the decrease of nitrogen concentration.

Determining Concentrations For Chemical Equilibria o In order to perform stoichiometric calculations for equilibrium systems we used something called an ICE table. “I” stands for initial concentration “C” stands for change in concentration “E” stands for equilibrium concentration Equation: I C E N 2(g) H 2(g) NH 3(g)

Example Problem #1 Hydrogen fluoride gas, HF(g) is used in the production of many important substances, such as medicines. Hydrogen fluoride may be synthesized from gaseous hydrogen, H 2(g) and fluorine, F 2(g). The initial concentration of hydrogen and fluorine is 2. 00 mol/L. No hydrogen fluoride gas is present initially. What are the equilibrium concentrations of hydrogen and hydrogen fluorine gas, if the equilibrium concentration of fluorine gas is 0. 48 mol/L?

Example Problem #1 Hydrogen fluoride gas, HF(g) is used in the production of many important substances, such as medicines. Hydrogen fluoride may be synthesized from gaseous hydrogen, H 2(g) and fluorine, F 2(g). The initial concentration of hydrogen and fluorine is 2. 00 mol/L. No hydrogen fluoride gas is present initially. What are the equilibrium concentrations of hydrogen and hydrogen fluorine gas, if the equilibrium concentration of fluorine gas is 0. 48 mol/L?

Example Problem #2 When ammonia gas, NH 3(g) is heated, it decomposes to form nitrogen gas, N 2(g) and hydrogen gas, H 2(g). A chemist adds 4. 0 mol of ammonia gas to a 2. 0 L sealed, rigid container and heats it. Below is a graph showing the changes in the amount of ammonia gas she observed over time. Determine the equilibrium concentrations of N 2(g) and H 2(g).

Example Problem #2 When ammonia gas, NH 3(g) is heated, it decomposes to form nitrogen gas, N 2(g) and hydrogen gas, H 2(g). A chemist adds 4. 0 mol of ammonia gas to a 2. 0 L sealed, rigid container and heats it. Below is a graph showing the changes in the amount of ammonia gas she observed over time. Determine the equilibrium concentrations of N 2(g) and H 2(g).

Homework 7. 1 Assignment is to be handed in before break. Answer Questions #1 -3 for extra practice.