Chemical Equilibrium Chemical equilibrium occurs when opposing reactions
Chemical Equilibrium Chemical equilibrium occurs when opposing reactions are proceeding at equal rates: The rate at which the products are formed from the reactants (from left to right) equals the rate at which the reactants are formed from the products (from right to left). Reactants ↔Products
The Concept of Equilibrium When a solid N 2 O 4, a colorless substance, warmed in a sealed flask above its boiling point, the colorless gas N 2 O 4 dissociates into brown NO 2 gas. Eventually, even though there is still N 2 O 4 in the flask, the color stops getting darker because the system reaches equilibrium N 2 O 4 (g)↔ 2 NO 2 (g) Colorless Brown If the decomposition of N 2 O 4 to form NO 2 the forward reaction, so the reaction of the NO 2 to re-form N 2 O 4 the reverse reaction. Forward reaction N 2 O 4 (g) → NO 2(g) Rate f = kf [N 2 O 4]
The Law of Mass Action and the Equilibrium Constant •
Homogeneous equilibrium •
Be careful: * Equilibrium expressions for gases can be reported in pressure (giving Kp) or in concentration (giving Kc). Kp = Kc (RT)Δn * Δn = sum of the products coefficients- sum of the reactants coefficients. * Kp = Kc when Δn = 0 * Dissolved species are reported in molar concentration (moles/L) * Pure solids and liquids DO NOT appear in the equilibrium expression. * K does NOT have units.
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