Exam 2 Review Flashcards
Equilibrium
A state in which both forward and reverse processes are ocurring at the same rate
Equilibrium constant
Kc or K<span>p</span>
A number equal to the ratio of the equilibrium concentrations of the products to the equilibrium concentrations of reactants, with each concentration raised to the power of its stoichiometric coefficient.
Remains constant at constant temperature.
Equilibrium expression
The quotient of the product concentrations and reactant concentrations, each raised to the power of its stoichiometric coefficient.
*No solids and liquids (pure) for heterogeneous reaction.
Law of mass action
For a reversible reaction at equilibrium and a constant temperature, the reaction quotient (Q) has a constant value (K – equilibrium constant).
Le Châtelier’s Principle
When a stress is applied to a system at equlibrium, the system will respond by shifting in the direction that minimizes the effect of the stress.
Reaction quotient
Qc or Qp
A fraction with product concentrations in the numerator and reactant concentrations in the denominator, each raised to its stoichiometric coefficient.
If Q < K, reaction goes to right
*If Q is less than K, forward reaction*
If Q > K, the reaction goes to the left
If Q = K, the system is in equilibrium
Reversible process
A process in which the products can react to form reactants.
Equilibrium constants and sides favored
Large constant (greater than 102) = PRODUCTS favored at equilibrium.
Small equilibrium constant (less than 10-2) = REACTANTS favored at equilibrium.
(Think of a chemical equation at equilibrium with a number line underneath, small numbers at left –> favors left/reactants.)
Manipulating Eq. Exp.: Reverse Equation?
Equilibrium constant (Kc) –> RECIPROCAL
Manipulating Eq. Exp.: Multiply Rxn by #?
Raise the equilibrium constant (Kc) by the power of #
Manipulating Eq. Exp.: Divide Rxn by #?
Take the [square/cubic/whatever] root of the equlibrium constant (Kc)
Manipulating Eq. Exp.: Add Rxn Equations?
Multiply the equlibrium constants together.
Equilibrium constant (pressure)
Kp = Kc [(0.08206 L * atm / K * mol) * T]Δn
Kp = Kc (RT)Δn
*when Δn = 0, Kp = Kc
Δn = PRODUCTS’ gaseous moles - REACTANTS’ gaseous moles
Relationship between free energy change and standard free energy change
ΔG = ΔGº + RT ln Q
R = 8.314 J/K*mol or 8.314*10-3 kJ/K*mol
T = in Kelvin
Q = reaction quotient (c or p)
If ΔG is positive, forward reaction is NONspontaneous.
If ΔG is negative, forward reaction is spontaneous.
If ΔG = 0, state of equilibrium.
Relationship between standard free energy change and equilibrium constant
ΔG° and K
ΔGº = -RT ln K
The larger K is, the more negative ΔG°.
If K greater than 1, ln K is positive, ΔG° is negative - products favored.
If K = 1, ln K = 0, ΔG° = 0, neither favored.
If K less than 1, ln K is negative, ΔG° is positive - reactants are favored.
Effect of addition to an equlibrium mixture
More reactant –> shifts toward products
More product –> shifts toward reactants
Effect of temperature change
Increasing temperature:
Endothermic rxn = shift toward products
Exothermic rxn = shift toward reactants
*Makes sense: add heat to endothermic rxn, which requires heat, more products formed.
Effect of volume change
Volume increase –> shift toward side with MORE moles of gas
Volume decrease –> shift toward side with FEWER moles of gas
Bronsted acid
Donates proton
Anion that remains = conjugate base
