4B6 Equilibrium in Chemical Systems Flashcards
Apply Le Chatelier’s principle and calculate equilibrium constants for chemical systems.
Define:
chemical equilibrium
The state where the rate of the forward reaction equals the rate of the reverse reaction in a closed system.
It ensures no net change in the concentration of reactants and products over time.
What is required for a reaction to reach equilibrium?
A closed system where no substances can enter or exit.
This prevents external influences from disrupting the balance of reactants and products.
Which type of arrow is used in reversible reactions?
Two opposing arrows (⇌).
This denotes that the reaction can proceed in both the forward and reverse directions.
Fill in the blank:
At dynamic equilibrium, the concentrations of reactants and products are _______.
constant
The term “dynamic” highlights the ongoing processes within the system.
Reactants and products are continuously converted into each other at equal rates, maintaining constant concentrations.
Even though individual molecules are in constant motion, their overall concentrations do not change.
Why is photosynthesis not a reversible reaction?
It only proceeds in the forward direction; converting carbon dioxide and water into sugar and oxygen.
This is shown by the single arrow (→) in the chemical equation.
What happens to a system when equilibrium is disrupted?
The system adjusts to restore equilibrium, maintaining constant concentrations of reactants and products.
This adjustment is explained by Le Chatelier’s principle.
How does the reaction arrow change if a reaction proceeds only in the forward direction?
A single arrow (→) replaces the reversible reaction arrows (⇌).
This indicates that the reaction does not proceed in the reverse direction.
True or False:
At equilibrium, the concentrations of reactants and products are always equal.
False
The concentrations are constant but not necessarily equal.
How does dynamic equilibrium differ from static equilibrium?
Dynamic equilibrium involves ongoing reactions in both directions, while static equilibrium involves no movement.
Chemical equilibrium is dynamic because of the continuous movement of molecules.
What is Le Chatelier’s Principle?
It describes how a system at equilibrium adjusts to external stressors to find a new equilibrium.
Le Chatelier’s Principle applies to changes in concentration, pressure, and temperature.
True or False:
Le Chatelier’s Principle has a specific mathematical formula.
False
The principle is conceptual and can be applied to equilibrium equations but lacks a unique formula.
What happens when pressure increases in a system with more molecules on the reactants side?
Equilibrium shifts to the right (towards products).
Increased pressure favors the side with fewer molecules to reduce collisions.
Fill in the blank:
Decreasing the volume of a gas system _______ the pressure.
increases
Boyle’s Law governs the inverse relationship between volume and pressure in gases.
True or False:
Equilibrium will not shift if pressure changes but the number of molecules is equal on both sides.
True
When molecule numbers are balanced, pressure changes do not affect equilibrium.
What happens to equilibrium when the pressure decreases in a system with more molecules on the product side?
It shifts to the left (toward reactants).
Lower pressure favors the side with more molecules to equalize collisions.
How can you increase the pressure of a gaseous system at equilibrium?
By decreasing the volume of the container.
Reducing container size confines particles, increasing collision frequency.
Define:
exothermic reaction
A reaction that releases heat; ΔH is negative.
In exothermic reactions, products have lower energy than reactants.
How does adding heat to an exothermic reaction affect equilibrium?
It shifts equilibrium to the left (toward reactants).
Heat is treated as a product in exothermic reactions, so adding heat favors the reverse reaction.
Fill in the blank:
Removing heat from an endothermic reaction shifts equilibrium to the _______ .
Left (towards reactants).
Heat is a reactant in endothermic reactions, so removing it favors the reverse reaction.
How does increasing reactant concentration affect equilibrium?
It shifts equilibrium to the right, favoring product formation.
Adding reactants increases the forward reaction rate, seeking to restore balance.
Define:
concentration
The amount of a substance in a defined space.
Concentration changes can shift equilibrium by altering reaction rates.
Define:
equilibrium constant
(K)
The product-to-reactant ratio at equilibrium in a reversible reaction, expressed as a formula involving the concentrations or partial pressures.
The equilibrium constant is temperature-dependent and remains unchanged unless the temperature changes.
What does a K > 1 value indicate?
The equilibrium state is product-heavy.
A K > 1 means the products are favored at equilibrium, with a larger numerator in the K expression.
Write the formula for K for the reaction: A + B ⇌ C + D (all aqueous species).
K = ([C][D]) / ([A][B])
The square brackets denote molar concentrations of the reactants and products at equilibrium.
What does Q represent in a reaction?
The reaction quotient.
Q is the product-to-reactant ratio at a specific moment, not necessarily at equilibrium.
Q is used to determine the direction a reaction will proceed to reach equilibrium.
How is Q calculated for gaseous species?
Q is calculated using the partial pressures of the products and reactants in the same formula as K.
The pressures are raised to the power of their coefficients in the balanced chemical equation.
How is K different from Q?
K is calculated using equilibrium concentrations, while Q uses concentrations at any given moment.
K remains constant at a fixed temperature, whereas Q changes as the reaction progresses.
True or False:
Solids and liquids are included in the expression for K and Q.
False
Solids and liquids are excluded because their concentrations are constant.
Fill in the blank:
If Q > K, the reaction will proceed _______.
backward
When Q > K, the system shifts to produce more reactants to reestablish equilibrium.
What happens when Q < K?
The reaction will proceed forward to produce more products.
This adjustment occurs to bring Q closer to K, achieving equilibrium.
True or False:
Q = K at equilibrium.
True
At equilibrium, the reaction quotient equals the equilibrium constant, indicating no net change in concentrations.
What does the Law of Mass Action state?
The reaction rate is proportional to the product of the concentrations of the reactants, raised to their coefficients in the balanced equation.
The Law of Mass Action forms the basis for the expression of the equilibrium constant, though it strictly applies to elementary reactions.
What is the equilibrium constant expression for the reaction 2A + B ⇌ 3C?
K = ([C]^3) / ([A]^2[B])
The coefficients in the balanced reaction are used as exponents for the concentrations in the K expression.
What is the equilibrium constant expression for the reaction aA+bB→cC+dD?
K = ([C]^c[D]^d) / ([A]^a[B]^b)
Only gases and aqueous compounds are included; solids and liquids are excluded.
What is the general purpose of equilibrium constant K in chemical reactions?
It indicates the extent to which a reaction favors the formation of products over reactants at equilibrium.
A large K (>1) means the reaction favors products, while a small K (<1) favors reactants.
What does the acronym RICE in a RICE table stand for?
- R: Reaction
- I: Initial concentration
- C: Change in concentration
- E: Equilibrium concentration
The RICE table is a systematic method used to solve equilibrium problems.
How do you calculate the ‘Change’ in a RICE table?
Subtract the initial concentration (I) from the equilibrium concentration (E).
The formula is C=E−I.
True or False:
Solids and liquids are included in RICE tables.
False
Solids and liquids do not factor into equilibrium constant calculations because their concentrations are constant.
What is the purpose of a RICE table?
To organize data related to a reaction’s equilibrium, stoichiometry, and reactant/product concentrations to solve equilibrium problems.
RICE tables are also called ICE charts or equilibrium tables.
Which quantities are entered in the ‘E’ row of a RICE table?
The equilibrium concentrations of all species involved in the reaction.
These values are either provided or calculated using known data and the equilibrium constant equation.
Fill in the blank:
In the reaction 2A+B→C, the change in concentration of A is represented as ______ in the RICE table.
−2X
The negative sign indicates a decrease, and the coefficient 2 reflects the stoichiometry.
True or False:
The RICE table can only solve for equilibrium constants.
False
RICE tables can also be used to find unknown reactant or product quantities given the equilibrium constant.
What does ‘initial concentration’ refer to in a RICE table?
The concentration of reactants and products before the reaction begins.
This is the starting point for calculating changes and equilibrium concentrations.
List the steps to use a RICE table to find Keq.
- Write the balanced reaction.
- Enter initial concentrations in the ‘I’ row.
- Define changes in ‘C’ row.
- Calculate equilibrium concentrations in ‘E’ row.
Plug equilibrium concentrations into the K formula to solve for the equilibrium constant.
How is the equilibrium concentration of a product calculated if the change is +X?
Add the initial concentration and the change: E=I+X.
This applies only when the product is being formed during the reaction.
Fill in the blank:
The change in concentration for a reactant is represented by a _______ value in the RICE table.
negative
Reactants are consumed in the reaction, so their change is negative.
What is the change in concentration for Y in the reaction 2X→Y+3Z if X decreases by 0.6 M?
0.3 M
The stoichiometry shows that 2 moles of X produce 1 mole of Y, so the change for Y is 0.6×1/2=0.3 M.
