Equilibrium Ms. Hoang ACP Chemistry

Concept of Equilibrium As a system approaches equilibrium, both the forward and reverse reactions are occurring. At equilibrium, the forward and reverse reactions are proceeding at the same rate.

System at Equilibrium Once Equilibrium is achieved, the amount of each reactant and product remains constant Think of a seesaw

Equilibrium Constant Ratio between concentration of products and concentration of reactants. aA+bB ↔cC+dD K= C c D d A a B b

Equilibrium Constant Example: Calculate the value of the equilibrium constant, K , for the system shown, if 0.1908 moles of CO2, 0.0908 moles of H2, 0.0092 moles of CO, and 0.0092 moles of H2O vapor were present in a 2.00 L reaction vessel were present at equilibrium. C O 2 g + H 2 g ↔C O g + H 2 O g

Equilibrium Constant CO2 0.1908 moles H2 0.0908 moles CO 0.0092 moles H2O 0.0092 moles C O 2 = H 2 = CO = H 2 O = C O 2 g + H 2 g ↔C O g + H 2 O g

Equilibrium Constant K= CO H 2 O C O 2 H 2 = (0.0046)(0.0046) (0.0954)(0.0454) = 0.0049 If K>1 reaction favors the products If K<1 reaction favors the reactants

What Does the Value of K Mean? If K >> 1, the reaction is product-favored; product predominates at equilibrium.

What Does the Value of K Mean? If K << 1, the reaction is reactant-favored; reactant predominates at equilibrium

Equilibrium Constant Equilibrium is temperature dependent At the same temperature, the system always comes to an equilibrium position such that K is constant regardless of the amounts of the reactants that are mixed together initially

Heterogeneous Equilibria CaC O 3 s ↔CaO s +C O 2 (g) Pure solids and liquids (except H2O) are not included in calculations of K

Energy and Equilibrium Which one has higher energy?

Energy and Equilibrium Energy of NO2 at 298K is 51.30kJ/mol Energy of N2O4 at 298K is 97.82kJ/mol N2O4 NO2