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Questions and Answers
What happens to a reaction at equilibrium when the concentration of a reactant is increased?
What happens to a reaction at equilibrium when the concentration of a reactant is increased?
How does increasing pressure affect a gaseous reaction at equilibrium?
How does increasing pressure affect a gaseous reaction at equilibrium?
For an exothermic reaction, what effect does raising the temperature have on the equilibrium?
For an exothermic reaction, what effect does raising the temperature have on the equilibrium?
What characterizes a strong electrolyte in solution?
What characterizes a strong electrolyte in solution?
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What is the definition of a Brønsted-Lowry acid?
What is the definition of a Brønsted-Lowry acid?
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Which of the following statements about catalysts is true?
Which of the following statements about catalysts is true?
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What does a positive ΔH signify about a reaction?
What does a positive ΔH signify about a reaction?
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What is the expression for the acid dissociation constant (Ka) of a weak acid?
What is the expression for the acid dissociation constant (Ka) of a weak acid?
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What does the equilibrium constant Kb represent for a weak base?
What does the equilibrium constant Kb represent for a weak base?
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In polyprotic acids, which statement about Ka values is accurate?
In polyprotic acids, which statement about Ka values is accurate?
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What does a lower pKa value indicate about an acid?
What does a lower pKa value indicate about an acid?
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What effect occurs when a common ion is added to a solution of a weak electrolyte?
What effect occurs when a common ion is added to a solution of a weak electrolyte?
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What type of solution results from the hydrolysis of a strong acid and a weak base?
What type of solution results from the hydrolysis of a strong acid and a weak base?
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How do buffer solutions work to resist changes in pH?
How do buffer solutions work to resist changes in pH?
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What conclusion can be drawn about a solution where IP equals Ksp?
What conclusion can be drawn about a solution where IP equals Ksp?
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Which mixture would likely create an acidic buffer solution?
Which mixture would likely create an acidic buffer solution?
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What impact does an increase in pKb have on the base strength?
What impact does an increase in pKb have on the base strength?
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What is the primary role of the blood buffer in the human body?
What is the primary role of the blood buffer in the human body?
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Study Notes
Le Chatelier's Principle
- Reactions always oppose changes in conditions to attempt to reach equilibrium.
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Concentration Effects:
- Increasing a reactant's concentration drives the reaction forward to consume the added reactant.
- Decreasing a reactant's concentration drives the reaction backward to produce more of that reactant.
- Increasing a product's concentration drives the reaction backward to consume the added product.
- Decreasing a product's concentration drives the reaction forward to produce more of that product.
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Pressure Effects:
- Reactions shift to favor the side with fewer moles of gas when pressure is increased (to reduce pressure).
- Reactions favor the side with more moles of gas when pressure is decreased (to increase pressure).
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Temperature Effects:
- Endothermic Reactions: Raising the temperature drives the reaction forward (heat is added as a reactant).
- Exothermic Reactions: Raising the temperature drives the reaction backward (heat is added as a product).
- Determining Endothermic/Exothermic: Look for the sign of ΔH (enthalpy change). A positive ΔH indicates an endothermic reaction and a negative ΔH indicates an exothermic reaction.
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Catalyst Effects:
- Catalysts do not alter the equilibrium position; they only speed up the rate at which equilibrium is reached.
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Inert Gas Effect:
- Inert gases (noble gases), which do not participate in the reaction, generally have no effect on the equilibrium position.
Acid-Base Definitions
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Arrhenius:
- An acid is a substance that produces H+ ions in solution.
- A base is a substance that produces OH- ions in solution.
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Brønsted-Lowry:
- An acid is a proton (H+) donor.
- A base is a proton acceptor.
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Lewis:
- An acid is an electron pair acceptor.
- A base is an electron pair donor.
Electrolytes
- Electrolytes are substances that produce ions in solution, capable of conducting electricity.
- Strong Electrolytes: Dissociate completely in solution, resulting in no equilibrium.
- Weak Electrolytes: Dissociate partially in solution, resulting in an equilibrium between the dissociated and undissociated forms.
Dissociation Constants
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Weak Acid Dissociation:
- Ka = equilibrium constant for a weak acid.
- Ka = [H+][A-]/[HA]
- Where [HA] is the concentration of the undissociated acid and [H+] and [A-] are the concentrations of the dissociated ions.
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Weak Base Dissociation:
- Kb = equilibrium constant for a weak base.
- Kb = [BH+][OH-]/[B]
- Where [B] is the concentration of the undissociated base and [BH+] and [OH-] are the concentrations of the dissociated ions.
Polyprotic Acids
- Polyprotic acids are acids capable of donating multiple protons.
- Each dissociation step has a corresponding Ka value (Ka1, Ka2, Ka3...).
- Ka values decrease (Ka1 > Ka2 > Ka3...), meaning the first dissociation step is favored over subsequent steps.
pKa and pKb
- pKa is the negative logarithm of the acid dissociation constant (Ka).
- pKb is the negative logarithm of the base dissociation constant (Kb).
- pKa + pKb = pKw = 14 (for a conjugate acid-base pair).
- Relationship to Strength: A lower pKa value indicates a stronger acid, and a lower pKb value indicates a stronger base.
Common Ion Effect
- The common ion effect occurs when a soluble salt containing an ion that is already present in a solution of a weak electrolyte is added.
- This addition shifts the equilibrium to favor the undissociated form of the weak electrolyte, decreasing its ionization.
Salt Hydrolysis
- Salt hydrolysis is the process where a salt reacts with water to produce an acidic or basic solution.
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Types of Salt Hydrolysis:
- Strong Base + Weak Acid -> Basic solution.
- Strong Acid + Weak Base -> Acidic solution.
- Weak Acid + Weak Base -> Solution can be acidic, basic, or neutral, depending on the relative strengths of the acid and base.
Buffer Solutions
- Buffers are solutions that resist changes in pH upon addition of small amounts of acid or base.
- Components of a Buffer: A buffer solution contains a weak acid (or base) and its conjugate base (or acid).
- Mechanism: The buffer components react with any added acid or base, minimizing the change in pH.
Key Terms
- Equilibrium: A state where the forward and reverse rates of a reversible reaction are equal.
- Dissociation: The process of a compound separating into its constituent ions.
- Hydrolysis: The reaction of a compound with water.
- Conjugate Acid-Base Pair: Two species differing by the presence or absence of a proton (H+).
Blood Buffer
- The human body maintains a neutral pH using a blood buffer solution, preventing large pH changes due to consumed acids or bases.
- The buffering capacity is limited; excessive consumption of acids or bases will result in pH shifts.
Buffer Solutions
- Buffer solutions resist pH changes upon addition of acids or bases.
- Acidic buffer: Formed by mixing a weak acid and its salt with a strong base.
- Basic buffer: Formed by mixing a weak base and its salt with a strong acid.
- Neutral buffer: Formed by mixing a weak acid with a weak base.
Solubility Product
- Solubility product (Ksp) indicates the extent a substance dissolves in water.
- Ksp is the product of the concentration of ions in a saturated solution.
- Higher Ksp indicates greater solubility.
- If ionic product (IP) > Ksp, precipitation (formation of a solid) occurs.
- If IP < Ksp, the solution is unsaturated; the solid will continue dissolving until IP = Ksp.
- If IP = Ksp, the solution is saturated, containing the maximum amount of dissolved solid at that temperature.
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Description
Explore the key concepts of Le Chatelier's Principle and how different factors such as concentration, pressure, and temperature affect chemical equilibrium. This quiz will test your understanding of equilibrium reactions and their responses to changes in conditions.
