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Quizzes > High School Quizzes > Science

Chemical Reaction Practice Quiz: Master Equilibrium

Ace Chemical Equilibrium with Problems and Lab Answers

Difficulty: Moderate
Grade: Grade 12
Study OutcomesCheat Sheet
Colorful paper art promoting the Chemical Equilibrium Challenge trivia quiz for chemistry students.

What is chemical equilibrium?
A state in which only reactant concentration changes
A state where only product concentration increases
A state in which the concentrations of reactants and products remain constant over time due to equal forward and reverse reaction rates
A state where reactions stop entirely
Chemical equilibrium is characterized by the state in which both the forward and reverse reactions occur at the same rate, resulting in constant concentrations of reactants and products. This dynamic balance is a fundamental concept in reversible reactions.
Which symbol is used to represent the equilibrium constant in a reaction's equilibrium expression?
C
E
K
Q
The equilibrium constant is denoted by K and is used to express the ratio of the concentrations of products to reactants at equilibrium. It is a key parameter in determining the extent of a reaction.
In an exothermic reaction at equilibrium, what does the addition of heat do according to Le Chatelier's Principle?
Increases the equilibrium constant
Shifts the equilibrium towards the products
Shifts the equilibrium towards the reactants
Has no effect on the equilibrium
In an exothermic reaction, heat acts like a product. When additional heat is added, the equilibrium shifts to favor the reverse reaction, which consumes heat. Thus, the equilibrium shifts towards the reactants.
In a chemical equilibrium system, if no changes are made to the system, why do the concentrations remain constant?
The rates of the forward and reverse reactions are equal
Energy flows out of the system
The reaction has stopped
Only the reactants are consumed completely
At equilibrium, the forward and reverse reactions occur at the same rate, leading to unchanging concentrations of reactants and products over time. This is the defining characteristic of chemical equilibrium.
Which of the following best describes a reversible reaction?
A reaction that proceeds only in one direction
A reaction that does not involve a catalyst
A reaction that always reaches equilibrium instantaneously
A reaction that can proceed in both forward and backward directions
A reversible reaction is one in which the reactants form products and those products can convert back into reactants. This bidirectional process eventually leads to a state of equilibrium.
How does increasing the concentration of reactants affect the equilibrium of a reaction?
It increases the equilibrium constant
It has no effect on the equilibrium
It shifts the equilibrium towards the reactants
It shifts the equilibrium towards the products
According to Le Chatelier's Principle, increasing the concentration of the reactants disturbs the equilibrium. The system responds by shifting towards the products to reduce the effect of the added reactants, though the equilibrium constant remains unchanged.
What is the reaction quotient (Q) used for in relation to equilibrium?
To measure the concentration of one reactant
To predict the direction in which a reaction will proceed to reach equilibrium
To represent the rate of the forward reaction
To indicate the temperature change in a reaction
The reaction quotient (Q) compares the current ratio of product to reactant concentrations with the equilibrium constant (K). It helps predict whether the forward or reverse reaction will occur to achieve equilibrium.
For the reaction aA + bB ⇌ cC + dD, what is the correct expression for the equilibrium constant (Kc)?
Kc = ([A]^a [B]^b) / ([C]^c [D]^d)
Kc = ([C]^c [D]^d) / ([A]^a [B]^b)
Kc = ([C] + [D]) / ([A] + [B])
Kc = (a[A] + b[B]) / (c[C] + d[D])
The equilibrium constant Kc is expressed as the ratio of the products' concentrations raised to their respective stoichiometric coefficients to those of the reactants. This expression remains constant at a given temperature.
Which condition is the only one that changes the value of the equilibrium constant (K) for a reaction?
A change in the pressure
A change in the temperature
The addition of a catalyst
A change in the concentration
The equilibrium constant (K) is solely dependent on the temperature of the system. While changes in concentration, pressure, or the addition of a catalyst can shift the equilibrium position, they do not alter K.
What does Le Chatelier's Principle predict about a system at equilibrium when the pressure is increased by decreasing the volume of a gaseous reaction system?
The equilibrium shifts towards the side with fewer gas molecules
The equilibrium shifts towards the side with more gas molecules
The reaction rate decreases
The equilibrium remains unchanged
When the pressure is increased by reducing volume, the system reacts by shifting towards the side with fewer gas molecules to reduce the pressure. This is a direct prediction of Le Chatelier's Principle in gaseous systems.
Which of the following expressions correctly represents the reaction quotient (Q) for the reaction: 2NO₂ ⇌ N₂O₄?
Q = [NO₂]² / [N₂O₄]
Q = [NO₂] / [N₂O₄]²
Q = [N₂O₄] / [NO₂]²
Q = 2[N₂O₄] / [NO₂]
For the reaction 2NO₂ ⇌ N₂O₄, each NO₂ is raised to the power of 2 reflecting its stoichiometric coefficient. Therefore, the correct reaction quotient expression is Q = [N₂O₄] / ([NO₂]²).
When a catalyst is added to a system at equilibrium, what is altered?
The enthalpy change of the reaction
The rate at which equilibrium is reached
The equilibrium constant value
The equilibrium position
A catalyst increases the speed of both the forward and reverse reactions equally, thereby helping the system reach equilibrium faster without affecting the equilibrium position or the equilibrium constant.
Why does an increase in temperature decrease the equilibrium constant for an exothermic reaction?
Because the pressure increases
Because the reaction shifts to favor the reactants
Because the catalyst becomes less effective
Because the reaction shifts to favor the products
In an exothermic reaction, heat is released as a product. Increasing the temperature adds heat to the system, prompting the equilibrium to shift towards the reactants (the endothermic direction) in order to absorb the excess heat. This shift results in a lower equilibrium constant.
For the reaction: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), what effect does removing CO₂ have on the system?
The equilibrium remains unchanged
The equilibrium shifts to the left
The equilibrium shifts to the right to produce more CO₂
The equilibrium constant increases
Removing CO₂ from the system decreases its concentration, causing a disturbance in equilibrium. To counteract this change, the equilibrium shifts to the right to produce more CO₂, in accordance with Le Chatelier's Principle.
How is the value of the equilibrium constant affected when a reaction is endothermic and the temperature is increased?
It depends on the catalyst
The equilibrium constant decreases
The equilibrium constant increases
The equilibrium constant remains unchanged
For an endothermic reaction, heat is treated as a reactant. Increasing the temperature provides more heat, which shifts the equilibrium towards the products and results in an increase in the equilibrium constant.
Given the equilibrium reaction: 2A + B ⇌ 3C, if the system is disturbed by decreasing the concentration of B, analyze how the reaction quotient (Q) compares to the equilibrium constant (K) and predict the shift in equilibrium.
Q = K, so no shift occurs
Q < K, so the equilibrium shifts to produce more C
Q < K, so the equilibrium shifts to produce more A and B
Q > K, so the equilibrium shifts to produce more A and B
Reducing the concentration of B causes a decrease in the value of Q relative to K because fewer reactant molecules are available. To re-establish equilibrium, the system shifts to the right, producing more of product C until Q equals K.
How does the addition of an inert gas at constant volume affect the position of equilibrium for a gaseous reaction?
It has no effect on the equilibrium position
It shifts the equilibrium to the side with more moles of gas
It increases the equilibrium constant
It shifts the equilibrium to the side with fewer moles of gas
Adding an inert gas at constant volume does not change the partial pressures of the reacting gases. Therefore, the equilibrium position remains unchanged as the system's composition is not affected.
In a reaction where Kc is defined as 0.05 at a certain temperature, what does this indicate about the reaction mixture at equilibrium?
The reactants are favored over the products
The reaction has a high rate of conversion to products
The products are favored over the reactants
The reaction is at exact stoichiometric balance
A small equilibrium constant (Kc < 1) means that the concentration of reactants is higher compared to the concentration of products at equilibrium. Thus, the reaction mixture favors the reactants.
Consider a reaction in a closed system at equilibrium. If the reaction is endothermic, what would be the effect of decreasing the temperature on both the equilibrium position and K?
The equilibrium shifts towards the reactants and K decreases
The equilibrium shifts towards the products and K increases
The equilibrium remains unchanged but K decreases
The equilibrium shifts towards the reactants but K increases
In an endothermic reaction, heat is a reactant. Decreasing the temperature removes heat from the system, causing the equilibrium to shift towards the reactants. This results in a decrease in the equilibrium constant (K).
For a complex equilibrium system involving multiple reactions, how can the principle of Le Chatelier be used to determine the net shift when a disturbance is applied?
By only considering the reaction with the highest equilibrium constant
By assuming the disturbance only affects the production of gases
By analyzing the system's individual equilibria and predicting the shift for each before determining the overall effect
By evaluating the change in temperature only
In complex systems, each equilibrium is first analyzed to understand how it responds to the disturbance according to Le Chatelier's Principle. The overall net shift is then determined by considering the combined effects of these individual shifts.
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Study Outcomes

  1. Understand the foundational principles of chemical equilibrium.
  2. Analyze the impact of temperature, pressure, and concentration changes on equilibrium systems.
  3. Apply Le Chatelier's principle to predict the direction of equilibrium shifts.
  4. Evaluate reaction quotients and equilibrium constants to determine reaction conditions.
  5. Solve quantitative problems involving dynamic equilibrium in chemical reactions.

Chemical Equilibrium Quiz & Practice Cheat Sheet

  1. Understanding Chemical Equilibrium - When the forward and reverse reactions are racing at the same speed, they meet at a dynamic hangout called equilibrium! No more changes in concentrations mean you've cracked the code on predicting where the reaction will chill out. Wikipedia: Chemical Equilibrium
    2. en.wikipedia.org/wiki/Chemical_equilibrium
  2. Equilibrium Constant (K) - Think of K as the scoreboard: a big number means products are dominating, while a tiny number means reactants hold the home advantage. By comparing product and reactant concentrations, K tells you which side the reaction favors at equilibrium. HyperPhysics: Equilibrium Constant
    3. hyperphysics.phy-astr.gsu.edu/hbase/Chemical/chemequi.html
  3. Reaction Quotient (Q) - Q is the sneak peek at your reaction's current score before halftime (equilibrium). If Q < K, the reaction pushes forward like an eager sprinter; if Q > K, it backpedals to catch up. Wikipedia: Reaction Quotient
    4. en.wikipedia.org/wiki/Reaction_quotient
  4. Le Châtelier's Principle - When you poke or prod a balanced system - by changing concentration, temperature, or pressure - it fights back to restore balance. It's chemistry's version of "don't mess with me" in action! Wikipedia: Le Châtelier's Principle
    5. en.wikipedia.org/wiki/Le_Chatelier%27s_principle
  5. Homogeneous vs. Heterogeneous Equilibria - Homogeneous means all players (reactants and products) share the same phase team - gas, liquid, or solid - while heterogeneous mixes phases like oil and water. Spotting the difference keeps you from writing bad equilibrium expressions. OpenStax: Key Terms
    6. openstax.org/books/chemistry-2e/pages/13-key-terms
  6. Law of Mass Action - This law says reaction rates are party favors from each reactant, multiplied together and raised to the power of their coefficients. It's the mathematical MVP behind why equilibrium constants look the way they do! OpenStax: Law of Mass Action
    7. openstax.org/books/chemistry-2e/pages/13-key-terms
  7. Calculating Kc and Kp - Use concentrations for Kc and partial pressures for Kp, then connect them with Kp = Kc(RT)Δn, where Δn is the moles of gas gained or lost. It's like converting kilometers to miles - same road, different units. HyperPhysics: Kc vs Kp
    8. hyperphysics.phy-astr.gsu.edu/hbase/Chemical/chemequi.html
  8. Effect of Temperature on Equilibrium - Turn up the heat and endothermic reactions get a boost, shifting equilibrium toward products. Cool things down and exothermic reactions take the limelight, swinging equilibrium back toward reactants. Wikipedia: Temperature Effects
    9. en.wikipedia.org/wiki/Le_Chatelier%27s_principle
  9. Role of Catalysts - Catalysts are the ultimate reaction personal trainers: they speed up both forward and reverse workouts equally, helping the system hit equilibrium faster without changing the final score. Wikipedia: Catalysts
    10. en.wikipedia.org/wiki/Le_Chatelier%27s_principle
  10. Gibbs Free Energy and Equilibrium - The magic formula ΔG° = −RT ln K links spontaneity with the equilibrium constant. If ΔG° is negative, products win; if it's positive, reactants reign supreme. PSU Unizin: Key Equations
    11. psu.pb.unizin.org/eshanichemistry110/chapter/key-terms-key-equations-summaries-and-exercises-chapter-13
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