Gen Chem Final Exam Flashcards
3How can the value of Kc be calculated?
Using the equilibrium concentrations of reactants and products.
What does a small Kc value distinguish?
More reactants than products.
- little reaction takes place
What does a large Kc value distinguish?
More products than reactants
- reaction is essentially complete
What does it mean when the Kc = 1?
Reactants = Products
- moderate reaction
What does the size of the equilibrium constant not affect?
How fast the equilibrium is reached.
Reaction Quotient (Qc)
Qc = [products]/[reactants]
- same as Kc
What happens if Qc=Kc?
-Reactant and product concentrations are equilibrium concentrations
-Reaction mixture is at equilibrium
What happens if Qc≠Kc?
-Reactant concentrations are NOT equilibrium concentrations
-Reaction mixture is NOT at equilibrium
Le Chatelier’s Principle
When a stress (a change) is placed on a reaction at equilibrium.
How does the system respond to stress (changes)?
Momentarily changing the rate of the forward/reverse reaction in the direction.
= Relieves that stress until the equilibrium is re-established
What happens to the rate of reaction when more reactant is added?
Rate of forward reaction increases to form more products until the system re-establishes equilibrium.
What happens to the equilibrium when more reactants are added?
The equilibrium shifts toward the products (forward direction)
What happens to the rate of reaction when reactant is removed?
Rate of the reverse reaction increases to form more reactant until the system re-establishes the equilibrium.
What happens to the equilibrium when reactants are removed?
The equilibrium shifts toward the reactants (reverse direction)
What happens to the rate of reaction when more product is added?
Rate of the reverse reaction increases to consume the product until the system re-establishes the equilibrium
What happens to the equilibrium when more products are added?
The equilibrium shifts toward the reactants (reverse direction)
What happens to the rate of reaction when product is removed?
The rate of the forward reaction increases to form more products until the system re-establishes equilibrium.
What happens to the equilibrium when products are removed?
The equilibrium shifts toward the products (forward direction).
What does changing the volume of a gas mixture at equilibrium cause?
Change in the concentration of gases in the mixture
What happens to the pressure of a mixture when the volume is decreased?
The pressure increases
What happens to the concentration of a mixture when the volume is decreased?
The concentration increases
What happens to the equilibrium when the volume is decreased?
The equilibrium shifts in the direction of the smaller number of moles to compensate.
What happens to the pressure of a mixture when the volume is increased?
The pressure decreases
What happens to the concentration of a mixture when the volume is increased?
The concentration decreases
What happens to the equilibrium when the volume is increased?
The equilibrium shifts in the direction of the larger number of moles to compensate.
What effect does volume/pressure change have on a reaction with the same amount of reactants and products?
NO EFFECT
What happens to the rate of reaction when temperature is increased in ENDOTHERMIC reactions?
The rate of the forward reaction increases to consume the added heat energy until the system re-establishes equilibrium.
What happens to the equilibrium when temperature is increased in ENDOTHERMIC reactions?
The equilibrium shifts toward the products (forward direction)
What happens to the rate of reaction when temperature is decreased in ENDOTHERMIC reactions?
The rate of the reverse reaction increases to generate more heat energy until the system re-establishes the equilibrium.
What happens to the equilibrium when temperature is decreased in ENDOTHERMIC reactions?
The equilibrium shifts toward the reactants (reverse direction).
What happens to the rate of reaction when temperature is increased in EXOTHERMIC reactions?
The rate of the reverse reaction increases to consume the added heat energy until the system re-establishes the equilibrium.
What happens to the equilibrium when temperature is increased in EXOTHERMIC reactions?
The equilibrium shifts toward the reactants (reverse direction).
What happens to the rate of reaction when temperature is decreased in EXOTHERMIC reactions?
The rate of the forward reaction increases to generate more heat until the system re-establishes the equilibrium.
What happens to the equilibrium when temperature is decreased in EXOTHERMIC reactions?
The equilibrium shifts toward the products (forward direction)
How does the addition of a catalyst affect the rate of reaction?
Speeds up a reaction by lowering the activation energy, which increases the rate of the forward and reverse reactions equally.
Are the ratios of reactants and products changed when a catalyst is added?
No; only the time to reach equilibrium is shorter
Does the addition of a catalyst shift the equilibrium?
No
What are the 5 properties of acids?
- Have a sour taste
- Have a stinging feel
- Turn litmus paper red
- Neutralize bases
- Corrode some metals
What are the 4 properties of bases?
- Have bitter (chalky) taste
- Have a soapy (slippery) feel
- Turn litmus paper blue
- Neutralize acids
What is the rule of naming a hydrogen ion and nonmetal?
- Use the prefix “hydro”
- End with “ic acid”
Example:
Hydrochloric Acid
What is the rule of naming a hydrogen ion and polyatomic group?
If it ends in “ate”
add “ic acid” to the end
add “ous acid” to the end
What is the exception to naming acids?
HCN: Hydrocyanic Acid
- Only follows rule 1
How do you name bases?
Add “hydroxide” to the end of the first element
What is the exception to naming bases?
NH3: Ammonia
Monoprotic Acids
Have only one reactive H+ that can be donated.
Diprotic Acids
Have two reactive H+ that can be donated
Triprotic Acids
Have three reactive H+ that can be donated
Do all hydrogen ions react?
NO
How can bases be categorized?
- Monobasic
-Dibasic
-Tribasic
(based on the number of OH- ions)
Are categorizing bases or acids more common?
Acids
What are acids and bases both considered?
Electrolytes
Why are acids and bases considered electrolytes?
They produce ions when dissolved in water.
Arrhenius Definition of Acids
Acids produce hydrogen ions when dissolved in water.
Arrhenius Definition of Bases
Bases produce hydroxide ions when dissolved in water
What is distinct about ammonia and forming hydroxide ions?
Ammonia tests as a base but does not have OH- in the formula.
What is a problem with the Arrhenius definition of bases and acids?
The definition is too narrow
Bronsted-Lowry Definition of Acids
Acids donate hydrogen ions/protons when dissolved in water
- lose H+
What does the Bronsted-Lowry Definition of Acids expand on?
The Arrhenius definition of bases and acids
What hydronium ion should we know?
H3O+
Hydronium Ions
H+ bonded to a water molecule
Bronsted-Lowry definition of bases
Bases accept hydrogen ions/protons when dissolved in water
- Gain H+
What is the Bronsted-Lowry Theory summarized?
- An acid is a substance that loses H+
- A base is a substance that gains H+
Amphoteric Substances
Have the capability to act as both acids and bases in the solution
What are the 3 most common examples of amphoteric substances?
- HCO3-
- H2O
- HPO4 2-
When do amphoteric substances act as an acid?
When they react with a stronger base.
When do amphoteric substances act as a base?
When they react with a stronger acid.
Strong Acids
Completely dissociates into ions in aqueous solutions.
What are strong acids also known as?
Strong electrolytes
What arrow is used in a chemical reaction with strong acids?
Forward facing arrow
What are the 6 common strong acids?
- HCl
- HBr
- HI
- HNO3
- HClO4
- H2SO4
Weak Acids
Dissociates only slightly in water to form few ions in aqueous solutions
What are weak acids also known as?
Weak electrolytes
What arrow is used in a chemical reaction with weak acids?
Double arrow
What do we refer to an acid as when it is not apart of the strong acid list?
A weak acid
Strong Bases
Completely dissociate into ions in aqueous solutions
What are strong bases also known as?
Strong electrolytes
What are the 8 most common strong bases?
- LiOH
- NaOH
- KOH
- RbOH
- CsOH
- Ba(OH)2
- Sr(OH)2
- Ca(OH)2
Weak Base
Ionizes only slightly in water to form a few ions in an aqueous solution
What are stronger acids correlated with?
Weaker conjugate bases
What are stronger bases correlated with?
Weaker conjugate acids
What do aqueous reactions favor?
The direction from stronger chemical species to weaker chemical species.
What is meant when the product side of a reaction is favored?
Favors forward direction of equation
More products than reactants
What is meant when the reactant side of a reaction is favored?
Favors reverse direction of equation
More reactants than products
Reversible Reactions
Dissociations of weak acids and bases
Ka and Kb Formula
[products] / [reactants]
What is not included in the Ka and Kb formulas?
Pure solids (s) and liquids (l)
What is correlated with a Ka/Kb value less than 1?
Favors reverse reaction
- more reactants
What is correlated with a Ka/Kb value greater than 1?
Favors forward reaction
- more products
What is correlated with a Ka/Kb value equal to 1?
Equilibrium
- same number of products and reactants
The larger the Ka value…
the stronger the acid
The larger the Kb value…
the stronger the base
pKa formula
-log(Ka)
The smaller the pKa value…
the stronger the acid
What can two water molecules react to produce?
H3O+ and OH-
When there is a reaction with two water molecules, water acts as…
Both an acid and a base (amphoteric)
Kw
Water Dissociation Constant
What is the solution called when H3O+ and OH- concentrations are equal?
Neutral Solution
What is the solution called when the H3O+ concentration is larger than OH-?
Acidic Solution
What is the solution called when the OH- concentration is larger than the H3O+?
Basic Solution
What is used to describe the acidity/basicity of solutions?
The pH scale
What can be used. to determine the pH of a solution?
- pH meter (probe in solution)
- pH paper (paper with dye)
- Indicators that turn different colors corresponding to different pH values
What is the formula for pH?
pH = -log [H3O+]
Does pH have any units?
No
What does the change of 1 pH unit correspond to?
A tenfold change in H3O+ .
As pH decreases…
H3O+ increases
(negative log scale)
What values does the pH scale range from?
0-14
When is the pH of a solution acidic?
Values less than 7
When is the pH of a solution neutral?
Value = 7
When is the pH of a solution basic?
Values greater than 7
How do you find the given H3O+ value when you have the pH value?
Anti-log = 10^(-pH)
