EQUILIBRIUM LAW AND THE EQUILIBRIUM CONSTANT SECTION 7
EQUILIBRIUM LAW AND THE EQUILIBRIUM CONSTANT SECTION 7. 2
EQUILIBRIUM LAW Equilibrium Law – the mathematical description of a chemical system at equilibrium Equilibrium Constant (K) – a constant numerical value defining the equilibrium law for a given system; units are not included when giving the value of K
PRACTICE Write the equilibrium law equations for the following reactions: 1. H 2(g) + I 2(g) 2 HI(g) 2. CO(g) + H 2 O(g) H 2(g) + CO 2(g) 3. 2 Cl 2(g) + 2 H 2 O(g) 4 HCl(g) + O 2(g)
ANALYZING THE EQUILIBRIUM LAW Lets look at the following reaction: N 2(g) + 3 H 2(g) 2 NH 3(g) at 500 K
So, what does this tell us about the equilibrium constant? • The equilibrium constant will always be the same at a specific set of reaction conditions, regardless of the initial concentrations of the substrates Does this mean that the equilibrium constant is always the same for a given reaction? • No, the equilibrium constant will change depending on the temperature of the reaction
CALCULATING K 1. The following synthesis reaction proceeds in a closed vessel at 5000 C: N 2(g) + 3 H 2(g) 2 NH 3(g). Given the equilibrium concentrations of gaseous nitrogen, hydrogen and ammonia, respectively, are 1. 5 x 10 -5 mol/L, 3. 45 x 10 -1 mol/L and 2. 00 x 10 -4 mol/L, what is the equilibrium constant? 1. Calculate the decomposition reaction of ammonia under the same conditions with the same equilibrium concentrations.
HETEROGENEOUS EQUILIBRIA Homogeneous Equilibrium – a chemical equilibrium system in which all reactants and products are in the same state of matter, such as the gas state Heterogeneous Equilibrium – a chemical equilibrium system in which the reactants and products are present in at least two different states, such as gases and solids. For a heterogeneous equilibrium system: • the equilibrium position does not depend on the quantities of pure solids or liquids WHY? • The concentrations of pure solids and liquids do not change during a chemical reaction • Therefore: for heterogeneous equilibrium systems only the substances in the gas phase and/or in solution are included in the equilibrium constant
PRACTICE
EQUILIBRIUM CONSTANT AND THE EQUILIBRIUM POSITION • The equilibrium position of a reaction describes the relative concentrations of reactants and products in reaction. • The equilibrium constant, K, can be used to determine the equilibrium position • The magnitude of the equilibrium constant will tell us if the reaction favors the products (lies to the right) or favors the reactants (lies to the left) K >>> 1 lies far to the right K=1 lies in the center K <<< 1 lies to the left
HOMEWORK READ: 429 -436 ANSWER QUESTIONS: • Page 431: #1 -3 • Page 434 #1 • Page 436 #1, 2, 3, 5
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