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Equilibrium. Equilibrium Constant (K Values). The equilibrium constant ( Keq ) is a number showing the relationship between the concentration of the products and the reactants. Each raised to the power of its coefficient in a balanced equation.
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Equilibrium Constant (K Values) • The equilibrium constant (Keq) is a number showing the relationship between the concentration of the products and the reactants. • Each raisedto the power of its coefficientin a balanced equation. • True for reversible reactions (go both forwards and backwards).
Equilibrium Constant Equation • Keq = [Products]coefficients [Reactants]coefficients • Reactants on the left and products on the right • Concentration (molarity) is represented by putting a [bracket] around a formula. • Only use [GASES (g)] and [AQUEOUS (aq)] compounds in Keq expressions because [SOLIDS (s)] and [LIQUIDS (l)] have no concentrations, so they do not need to be included.
Example 3H2(g) + N2(g) 2NH3(g) • Write the equilibrium expression for the reaction above: • Keq = [NH3]2 [H2]3 [N2]1 • C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(l) • Write the equilibrium expression for the reaction above: • The [H2O] is not used because it’s a liquid. • Keq = [CO2]3 [C3H8] [O2]5
What does the calculated value for Keq tell us? A. Keq = 1 means that AT EQUILIBRIUM the [products] = [reactants] B. Keq > 1 means that AT EQUILIBRIUM the [products] > [reactants] C. Keq < 1 means that AT EQUILIBRIUM the [products] < [reactants]
Example 1 A mixture of plenty of gaseous H2O and solid C are placed in a large container and allowed to come to equilibrium according to the following reaction: C (s) + H2O (g) CO (g) + H2 (g) • The equilibrium concentrations of the species are as follows: [H2O] = 0.56 M, [CO] = 0.33 M, and [H2] = 0.040 M. • What is the value of the equilibrium constant for this reaction? • Does this equilibrium constant show that there are more products, more reactants, or equal amounts of the products and reactants? AND, how do you know?
Answer • Keq = [CO] [H2] [H2O] • Keq = [0.33][0.040] [0.56] • = 0.024 • There are more reactants; the value of Keq is smaller than 1
Example 2 • Given: 2 SO2(g) + O2(g) 2 SO3(g) • The Keq= 6.67 • Write the equilibrium expression • Calculate the equilibrium concentration of [SO3] when… • [SO2] = 0.25 M and [O2] = 0.20 M
Example 3 • 2 SO2(g) + O2(g) 2 SO3(g) Keq = 6.67 • C (s) + H2O (g) CO (g) + H2 (g) Keq = 0.024 Which reaction favors the products most? WHY