Topic 7: Equilibrium Flashcards
What is chemical equilibrium?
A state in which the rate of the forward reaction equals the rate of backward reaction. Both reactions continue to occur, but the concentrations of products/reactants stays the same.
What are five characteristics of equilibrium?
Dynamic, closed system, concentrations stay the same, no change in macroscopic properties, can be reached from either direction
What does it mean that equilibrium is dynamic?
The reaction has stopped by the forward and reverse reactions still occur at the same rate.
What does it mean that equilibrium is achieved in a closed system?
No matter can escape the system
What does it mean that concentrations of products and reactants are the same for equilibrium?
Forward and reverse reactions occur at the same rate, so there is an equal concentration of products and reactants
What does it mean that a reaction at equilibrium has no change in macroscopic properties?
Visible properties, like color and density, do not change
What does it mean that equilibrium can be reached from either direction?
Backward and forward reactions can both arrive to equilibrium
What is the equilibrium constant represented as?
K subscript c
How can an equilibrium reaction be represented?
aA + bB <—-> cC + dD. The lowercase letters represent the molar coefficients, the uppercase letters represent the element symbol
How do you calculate Kc?
If aA + bB <—-> cC + dD, then Kc=
([C]^c x [D]^d) / ([A]^a x [B]^b). In other words, Kc is the concentration of the products raised to their molar coefficients over the concentration of reactants raised to their molar coefficients.
What does [X] represent?
The concentration of element X
Which elements/states should be included in a Kc calculation? Which elements/states should not
Only use gases and aqueous solutions. Liquids and solids don’t count!
How do you interpret Kc values?
If Kc > 1, reaction favors products. If Kc < 1, reaction favors reactants.
If Kc = 1, reaction is at equilibrium
What is the reaction quotient? How is it different from Kc?
It measures the relative amount of products/reactants at a certain time in the reaction. It is calculated the same way as Kc but Q is for reactions NOT at equilibrium.
How do you interpret Q in the context of Kc?
If Q=Kc, equilibrium.
If Q > Kc, Q will decrease to produce more reactants
If Q < Kc, Q will increase to produce more products
What do the expressions “lying to left” or “lying to right” mean?
Left=reaction favors reactants
Right=reaction favors products
What happens to Q as time passes?
It will eventually equal Kc as the reaction reaches equilibrium
What is Le Chatelier’s Principle?(which I will refer to as LCP for ease :)
If a dynamic equilibrium is disturbed by changing conditions, the position of equilibrium shifts to counteract the change and reestablish equilibrium
According to LCP, how does increasing or decreasing concentration shift the reaction?
Increasing the concentration shifts the reaction to favor the side with fewer moles of solute.
Decreasing the concentration shifts the reaction to favor the side with more moles of solute.
How does increasing or decreasing pressure shift the reaction according to LCP?
Increasing pressure shifts rxn to favor side with fewer moles of gas.
Decreasing pressure shifts rxn to favor side with more moles of gas.
What do you need to know about a reaction to determine how increasing or decreasing temp affects it?
If it’s endo/exo.
What is unique about temperature in terms of LCP and Kc?
It is the only factor that can change Kc and the position of equilibrium
How does increasing temperature affect an EXOthermic reaction?
In an exo rxn, heat is a product, so increasing heat shifts reaction to favor reactants
How does increasing temp affect an ENDOthermic rxn?
In endo, heat is a reactant, so increasing heat shifts rxn to favor products
Do catalysts have any effect on Kc?
No
