4B6 Equilibrium in Chemical Systems

Question 1

Define:

chemical equilibrium

Answer 1

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.

Question 2

What is required for a reaction to reach equilibrium?

Answer 2

A closed system where no substances can enter or exit.

This prevents external influences from disrupting the balance of reactants and products.

Question 3

Which type of arrow is used in reversible reactions?

Answer 3

Two opposing arrows (⇌).

This denotes that the reaction can proceed in both the forward and reverse directions.

Question 4

Fill in the blank:

At dynamic equilibrium, the concentrations of reactants and products are _______.

Answer 4

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.

Question 5

Why is photosynthesis not a reversible reaction?

Answer 5

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.

Question 6

What happens to a system when equilibrium is disrupted?

Answer 6

The system adjusts to restore equilibrium, maintaining constant concentrations of reactants and products.

This adjustment is explained by Le Chatelier’s principle.

Question 7

How does the reaction arrow change if a reaction proceeds only in the forward direction?

Answer 7

A single arrow (→) replaces the reversible reaction arrows (⇌).

This indicates that the reaction does not proceed in the reverse direction.

Question 8

True or False:

At equilibrium, the concentrations of reactants and products are always equal.

Answer 8

False

The concentrations are constant but not necessarily equal.

Question 9

How does dynamic equilibrium differ from static equilibrium?

Answer 9

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.

Question 10

What is Le Chatelier’s Principle?

Answer 10

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.

Question 11

True or False:

Le Chatelier’s Principle has a specific mathematical formula.

Answer 11

False

The principle is conceptual and can be applied to equilibrium equations but lacks a unique formula.

Question 12

What happens when pressure increases in a system with more molecules on the reactants side?

Answer 12

Equilibrium shifts to the right (towards products).

Increased pressure favors the side with fewer molecules to reduce collisions.

Question 13

Fill in the blank:

Decreasing the volume of a gas system _______ the pressure.

Answer 13

increases

Boyle’s Law governs the inverse relationship between volume and pressure in gases.

Question 14

True or False:

Equilibrium will not shift if pressure changes but the number of molecules is equal on both sides.

Answer 14

True

When molecule numbers are balanced, pressure changes do not affect equilibrium.

Question 15

What happens to equilibrium when the pressure decreases in a system with more molecules on the product side?

Answer 15

It shifts to the left (toward reactants).

Lower pressure favors the side with more molecules to equalize collisions.

Question 16

How can you increase the pressure of a gaseous system at equilibrium?

Answer 16

By decreasing the volume of the container.

Reducing container size confines particles, increasing collision frequency.

Question 17

Define:

exothermic reaction

Answer 17

A reaction that releases heat; ΔH is negative.

In exothermic reactions, products have lower energy than reactants.

Question 18

How does adding heat to an exothermic reaction affect equilibrium?

Answer 18

It shifts equilibrium to the left (toward reactants).

Heat is treated as a product in exothermic reactions, so adding heat favors the reverse reaction.

Question 19

Fill in the blank:

Removing heat from an endothermic reaction shifts equilibrium to the _______ .

Answer 19

Left (towards reactants).

Heat is a reactant in endothermic reactions, so removing it favors the reverse reaction.

Question 20

How does increasing reactant concentration affect equilibrium?

Answer 20

It shifts equilibrium to the right, favoring product formation.

Adding reactants increases the forward reaction rate, seeking to restore balance.

Question 21

Define:

concentration

Answer 21

The amount of a substance in a defined space.

Concentration changes can shift equilibrium by altering reaction rates.

Question 22

Define:

equilibrium constant

(K)

Answer 22

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.

Question 23

What does a K > 1 value indicate?

Answer 23

The equilibrium state is product-heavy.

A K > 1 means the products are favored at equilibrium, with a larger numerator in the K expression.

Question 24

Write the formula for K for the reaction: A + B ⇌ C + D (all aqueous species).

Answer 24

K = ([C][D]) / ([A][B])

The square brackets denote molar concentrations of the reactants and products at equilibrium.

Question 25

What does **Q represent** in a reaction?

Answer 25

The reaction quotient. ## Footnote 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.

Question 26

How is Q calculated for **gaseous species**?

Answer 26

Q is calculated **using the partial pressures** of the products and reactants in the same formula as K. ## Footnote The pressures are raised to the power of their coefficients in the balanced chemical equation.

Question 27

How is K **different** from Q?

Answer 27

K is calculated using equilibrium concentrations, while **Q uses concentrations at any given moment**. ## Footnote K remains constant at a fixed temperature, whereas Q changes as the reaction progresses.

Question 28

# True or False: Solids and liquids **are included** in the expression for K and Q.

Answer 28

False ## Footnote Solids and liquids are excluded because their concentrations are constant.

Question 29

# Fill in the blank: If **Q > K**, the reaction will proceed \_\_\_\_\_\_\_.

Answer 29

backward ## Footnote When Q > K, the system shifts to produce more reactants to reestablish equilibrium.

Question 30

What happens when **Q < K**?

Answer 30

The reaction will **proceed forward** to produce more products. ## Footnote This adjustment occurs to bring Q closer to K, achieving equilibrium.

Question 31

# True or False: Q = K at **equilibrium**.

Answer 31

True ## Footnote At equilibrium, the reaction quotient equals the equilibrium constant, indicating no net change in concentrations.

Question 32

What does the **Law of Mass Action** state?

Answer 32

The reaction rate is proportional to the product of the concentrations of the reactants, **raised to their coefficients** in the balanced equation. ## Footnote The Law of Mass Action forms the basis for the expression of the equilibrium constant, though it strictly applies to elementary reactions.

Question 33

What is the **equilibrium constant expression** for the reaction **2A + B ⇌ 3C**?

Answer 33

K = ([C]^3) / ([A]^2[B]) ## Footnote The coefficients in the balanced reaction are used as exponents for the concentrations in the K expression.

Question 34

What is the **equilibrium constant expression** for the reaction **aA+bB→cC+dD**?

Answer 34

K = ([C]^c[D]^d) / ([A]^a[B]^b) ## Footnote Only gases and aqueous compounds are included; solids and liquids are excluded.

Question 35

What is the general **purpose of equilibrium constant** K in chemical reactions?

Answer 35

It indicates the extent to which a reaction **favors the formation of products** over reactants at equilibrium. ## Footnote A large K (>1) means the reaction favors products, while a small K (<1) favors reactants.

Question 36

What does the **acronym RICE** in a RICE table stand for?

Answer 36

* **R**: Reaction * **I**: Initial concentration * **C**: Change in concentration * **E**: Equilibrium concentration ## Footnote The RICE table is a systematic method used to solve equilibrium problems.

Question 37

How do you **calculate** the '**Change**' in a RICE table?

Answer 37

**Subtract** the initial concentration (I) from the equilibrium concentration (E). ## Footnote The formula is C=E−I.

Question 38

# True or False: Solids and liquids **are included** in RICE tables.

Answer 38

False ## Footnote Solids and liquids do not factor into equilibrium constant calculations because their concentrations are constant.

Question 39

What is the **purpose** of a RICE table?

Answer 39

To organize data related to a reaction's equilibrium, stoichiometry, and reactant/product concentrations to **solve equilibrium problems**. ## Footnote RICE tables are also called ICE charts or equilibrium tables.

Question 40

Which quantities are entered in the '**E**' **row of a RICE table**?

Answer 40

The equilibrium concentrations **of all species involved** in the reaction. ## Footnote These values are either provided or calculated using known data and the equilibrium constant equation.

Question 41

# Fill in the blank: In the reaction **2A+B→C**, the **change in concentration of A** is represented as \_\_\_\_\_\_ in the RICE table.

Answer 41

−2X ## Footnote The negative sign indicates a decrease, and the coefficient 2 reflects the stoichiometry.

Question 42

# True or False: The RICE table can **only solve** for equilibrium constants.

Answer 42

False ## Footnote RICE tables can also be used to find unknown reactant or product quantities given the equilibrium constant.

Question 43

What does '**initial concentration**' refer to in a RICE table?

Answer 43

The concentration of reactants and products **before the reaction begins**. ## Footnote This is the starting point for calculating changes and equilibrium concentrations.

Question 44

List the **steps to use a RICE table** to find Keq.

Answer 44

1. Write the balanced reaction. 2. Enter initial concentrations in the 'I' row. 3. Define changes in 'C' row. 4. Calculate equilibrium concentrations in 'E' row. ## Footnote Plug equilibrium concentrations into the K formula to solve for the equilibrium constant.

Question 45

How is the **equilibrium concentration of a product** calculated if the change is +X?

Answer 45

Add the initial concentration and the change: **E=I+X**. ## Footnote This applies only when the product is being formed during the reaction.

Question 46

# Fill in the blank: The **change in concentration** for a reactant is represented by a \_\_\_\_\_\_\_ value in the RICE table.

Answer 46

negative ## Footnote Reactants are consumed in the reaction, so their change is negative.

Question 47

What is the change in concentration for Y in the reaction 2X→Y+3Z **if X decreases by 0.6 M**?

Answer 47

0.3 M ## Footnote 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.