Ch. 6: Equilibrium Flashcards
Define dynamic chemical equilibrium.
A B
The concentrations of A and B are constant but not necessarily equal. The rate of the forward and reverse reaction is equal. A reaction reaches equilibrium when entropy (energy distribution) is at a maximum and Gibb’s free energy is at minimum.
What is the unit of entropy?
J/Kmol
Distribution of energy throughout a system or between a system and its environment
What is the law of mass action equation?
For aA+bB→cC+dD,
Ke = [C]^c[D]^d / [A]^a[B]^b
What is the difference between Keq and Q?
Keq defines the position of the reaction equilibrium and is based on concentrations at equilibrium. Keq is a specific Q.
Q is the reaction position at any point.
How does the reaction proceed if Q < Keq?
When Q < Keq the forward reaction has not yet reached equilibrium. There is a greater concentration of reactants than equilibrium so the FORWARD rate is INCREASED to restore equilibrium.
How does the reaction proceed if Q = Keq?
The reaction is at dynamic equilibrium. The forward and reverse rates are equal.
How does the reaction proceed if Q > Keq?
When Q > Keq the forward reaction has exceeded equilibrium. There is a greater concentration of products than equilibrium so the REVERSE rate is INCREASED to restore equilibrium.
What is the ΔG when Q < Keq? Q = Keq? Q > Keq?
ΔG is negative when Q < Keq
ΔG is zero when Q = Keq
ΔG is positive when Q > Keq
What phases are left out of the equilibrium constant equation?
The concentrations of pure solids and pure liquids
What condition can alter Keq?
Temperature
Describe how a system responds when it is compressed.
When a system is compressed, volume decreases, and pressure increases. The increase in total pressure is associated with an increase in the partial pressures of each gas in the system. Therefore, the system is no longer at equilibrium.
The system will move towards whichever side has lower total number of moles of gas. As stated by the gas law (PV=nRT), an increase in moles increases pressure. Thus, the system will move to the side with less mole to decrease pressure.
How do Keq and Q change immediately after temperature changes? Why?
Keq changes immediately and depends on enthalpy.
Q does not because temperature does not cause the concentrations or partial pressure of the reactants and products to change immediately.
How does the system decide which direction to move in when temperature changes?
Enthalpy: When the reaction is endothermic (ΔH > 0), heat is a reactant. When the reaction is exothermic (ΔH < 0), heat is a product.
When a reaction endothermic is heat a product or reactant?
Reactant
When a reaction exothermic is heat a product or reactant?
Product
