Chemical Equilibria & Kc Flashcards

Interactive active recall cards for dynamic equilibrium, Le Chatelier's Principle, and Kc calculations.

Dynamic Equilibrium & Le Chatelier: read all 7 questions and answers

Define dynamic equilibrium.
A state in a closed system where the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.
State Le Chatelier's Principle.
If a system at equilibrium is subjected to a change in conditions, the system will shift its position of equilibrium to oppose the change.
What is a closed system?
A system in which matter cannot enter or leave, but energy can be exchanged with the surroundings.
Explain the effect of increasing temperature on the position of equilibrium for an exothermic forward reaction.
The position of equilibrium shifts to the left (in the endothermic direction) to absorb the added heat and oppose the change.
Explain the effect of increasing pressure on the position of equilibrium for a gaseous reaction.
The equilibrium shifts to the side with fewer moles of gas to decrease the pressure and oppose the change.
Explain the effect of increasing the concentration of a reactant on the position of equilibrium.
The equilibrium shifts to the right (towards the products) to consume the added reactant and oppose the change.
What is the effect of adding a catalyst on the position of equilibrium?
It has no effect on the position of equilibrium because it increases the rates of both the forward and reverse reactions by the same factor.

Equilibrium Constant Kc: read all 5 questions and answers

Write the general expression for the equilibrium constant \(K_c\) for the reaction: \(a\text{A} + b\text{B} \rightleftharpoons c\text{C} + d\text{D}\).
\(K_c = \frac{[\text{C}]^c [\text{D}]^d}{[\text{A}]^a [\text{B}]^b}\), where [X] represents the concentration of species X at equilibrium in mol dm⁻³.
How do you determine the units of \(K_c\)?
Substitute the unit 'mol dm⁻³' for each concentration term in the \(K_c\) expression and simplify the expression by cancelling terms.
If the value of \(K_c\) is very large (e.g. > 10³), what does this indicate about the position of equilibrium?
The equilibrium lies heavily to the right, meaning there is a high concentration of products relative to reactants at equilibrium.
If the value of \(K_c\) is very small (e.g. < 10⁻³), what does this indicate about the position of equilibrium?
The equilibrium lies heavily to the left, meaning there is a high concentration of reactants relative to products at equilibrium.
Outline the ICE method for calculating equilibrium moles.
Set up a table with columns for each reactant and product, and rows for Initial moles, Change in moles, and Equilibrium moles. Convert equilibrium moles to concentration by dividing by the volume.

Factors Affecting Kc: read all 6 questions and answers

Which factor is the only one that changes the value of the equilibrium constant \(K_c\)?
Temperature.
For an endothermic forward reaction, how does increasing the temperature affect the value of \(K_c\)?
The value of \(K_c\) increases because the equilibrium shifts to the right, raising the concentration of products and lowering the concentration of reactants.
For an exothermic forward reaction, how does increasing the temperature affect the value of \(K_c\)?
The value of \(K_c\) decreases because the equilibrium shifts to the left, lowering the concentration of products and raising the concentration of reactants.
Explain why changing the concentration of a reactant does not change the value of \(K_c\).
The concentrations of all species adjust so that the ratio in the \(K_c\) expression remains constant at that temperature.
Explain why adding a catalyst does not change the value of \(K_c\).
It increases the rate of both forward and reverse reactions equally, so the equilibrium concentrations remain unchanged, leaving the ratio constant.
Explain why changing the total pressure does not change the value of \(K_c\) for a gaseous reaction.
Although concentrations of gases change, they adjust so that their ratio in the \(K_c\) expression remains constant at that temperature.