Ch 6- Equilibrium Flashcards
“At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, entropy is at a _____, and Gibbs free energy is at a _____. This links the concepts of thermodynamics and kinetics.”
Maximum; Minimum
“Kc is called the ________ and the subscript c indicates that it is in terms of concentration. When dealing with gases, the equilibrium constant is referred to as _____, and the subscript p indicates that it is in terms of pressure”
equilibrium constant; Kp
“For dilute solutions, Keq = ____ and both are calculated in units of concentration.”
Kc
“While the forward and the reverse reaction rates are equal at equilibrium, the concentrations of the reactants and products are not usually equal. This means that the forward and reverse reaction rate constants, kf and kr, respectively, are not usually equal to each other. The ratio of kf to kr is Kc. Whats the equation
Kc=keq= kforward/kreverse
“When a reaction occurs in more than one step, the equilibrium constant for the overall reaction is found by multiplying together the equilibrium constants for each step of the reaction. ”
“if the reaction aA + bB ⇌ cC + dD occurs in three steps, each with a forward and reverse rate, then” Kc =
k1k2k3/k^-1K^-2K^-3=[C]^C[D]^D/[A]^A[B]^B
“What can serve as a “timer” to indicate how far the reaction has proceeded toward equilibrium? This role is served by _____
the reaction quotient, Q”
What is the significance if Q
-the forward reaction has not yet reached equilibrium.”
- There is a greater concentration of reactants (and smaller concentration of products) than at equilibrium.
- The forward rate of reaction is increased to restore equilibrium.”
What is the significance if Q=Keq? ΔG = 0
- the reaction is in dynamic equilibrium”
- The reactants and products are present in equilibrium proportions.
- The forward and reverse rates of reaction are equal.”
What is the significance if Q>Keq (ΔG>0)
- the forward reaction has exceeded equilibrium
- There is a greater concentration of products (and smaller concentration of reactants) than at equilibrium.
- The reverse rate of reaction is increased to restore equilibrium
“Any reaction in the equilibrium state will continue to react in the forward and reverse directions, but the reaction rates for the forward and reverse reactions will be _____, and the concentrations of the reactants and products will be ______, such that Q = Keq”
Equal; Constant
“The concentrations of ______ and _______ do not appear in the equilibrium constant expression.
pure solids and pure liquids
This is because the equilibrium expression is technically based on the activities of compounds, not concentrations; the activities of pure solids and liquids are defined to be 1”
“Keq is characteristic of a particular reaction at a given _______;
Temperature
the equilibrium constant is temperature-dependent.”
“The larger the value of Keq the farther _____
the farther to the right the equilibrium position.”
“If the equilibrium constant for a reaction written in one direction is Keq, the equilibrium constant for the reverse reaction is”
1/Keq
“states that if a stress is applied to a system, the system shifts to relieve that applied stress”
Le Châtelier’s principle
“ When the pressure of this system is increased, the system will react in the direction that produces _____ moles of gas. In this case, that direction is to the right, and more ammonia will form. However, if the pressure is decreased, the system will react in the direction that produces _____ moles of gas”
Fewer; more
“unlike the effect of changing concentrations or pressures, the result of changing temperature is not a change in the reaction quotient, Qc or Qp, but a change in”
Keq
“That direction is determined by the enthalpy of the reaction. If a reaction is endothermic (ΔH > 0), heat functions as a ______; if a reaction is exothermic (ΔH
Reactant; Product
“These reactants can undergo two different sets of reactions. At lower temperatures (with smaller heat transfer), a ______ product is formed. At higher temperatures (with larger heat transfer), a ______ product is formed”
Kinetic; Thermodynamic
“Note that the free energy that must be added for the kinetic pathway is lower than that of the thermodynamic pathway. Therefore, the kinetic products often form faster than the thermodynamic products and are sometimes called “fast” products. On the other hand, the free energy of the thermodynamic product is significantly lower than that of the kinetic product.”
“gives the expression for the equilibrium constant, Keq. The reaction quotient, Q, has the same form but can be calculated at any concentrations of reactants and products.”
The law of mass action
“Pure _____ and _____do not appear in the law of mass action; only gases and aqueous species do.”
“Pure solids and liquids
“There are three main types of stresses applied to a system: changes in
concentration, pressure and volume, and temperature.”
“Increasing the concentration of reactants or decreasing the concentration of products will shift the reaction to the _____
right
“Increasing pressure on a gaseous system (decreasing its volume) will shift the reaction toward the side with _____ moles of gas. Decreasing pressure on a gaseous system (increasing its volume) will shift the reaction toward the side with _____ moles of gas.”
Fewer; More
“Increasing the temperature of an endothermic reaction or decreasing the temperature of an exothermic reaction will shift the reaction to the _____. Decreasing the temperature of an endothermic reaction or increasing the temperature of an exothermic reaction will shift the reaction to the ______”
Right; Left
“Reactions may have both ______ and ______ products that can be regulated by temperature and the presence of a catalyst.”
kinetic and thermodynamic
“are higher in free energy than thermodynamic products and can form at lower temperatures. These are sometimes termed “fast” products because they can form more quickly under such conditions.”
Kinetic products
Are lower in free energy than kinetic products and are therefore more stable. Despite proceeding more slowly than the kinetic pathway, the thermodynamic pathway is more spontaneous (more negative ΔG).”
Thermodynamic Products
