Equilibrium Flashcards
What happens to the concentrations of reactants and products at when they reach equilibrium?
The concentrations of the reactants and products become constant, even if they aren’t always equal. They stop changing and the reaction continuously and dynamically continues in both directions.
At chemical equilibrium, does the rate of reaction in the forward direction equal the rate of reaction in the reverse direction?
Yes
Does it matter what mixture of reactants and products equilibrium originates from?
No, chemical equilibrium can originate from a mixture of reactants and products or a pure reactants and pure products.
What is the equilibrium constant K a ratio of?
The concentrations (or partial pressures) or reactants and the concentrations (or partial pressures) of products at equilibrium. K = [products]^nu/[reactants]^nu, where nu is the stoichiometric coefficient.
What is the reaction quotient Q?
Q is a measure of the progression of a reversible reaction in non-equilibrium conditions. It is a ratio of concentrations or a ratio of partial pressures of reactants and products to the powers of their stoichiometry. Q = [products]^nu/[reactants]^nu, where nu is the stoichiometric coefficient.
How are Q or K (partial pressures) and Q or K (concentration) related?
Pressure = concentration * (RT)^(deltanu) where delta nu is the difference in stoichiometric coefficients
What happens when Q(c) > K(c)?
If Q > K then that means that products is greater than reactants. So the reaction goes towards reactants to establish equilibrium.
What happens when Q(c) < K(c)
If Q < K, then that means products is less than the reactants. So the reaction goes towards products to establish equilibrium.
What is activity when talking about equilibirum constant k?
Activity is the concentration or partial pressures as a ratio to respect with a standard reference state (pressure, temp)
When K < 1 at equilibrium
More reactants than products
When K ~ 1 at equilibrium
Similar amts of reactants and products
When K > 1 at equilibrium
More products than reactants
What phases are not included in the equilibrium constant expression?
Pure solids, liquids and solvents since their concentrations/activities are considered constant and equal to one.
What is the definition of Le Chatelier’s principle?
When a reaction mixture at equilibrium is disturbed to non-equilibrium concentrations, the concentrations will change to counteract the disturbance and re-establish equilibrium.
According to Le Chatelier, what happens to equilibrium when there is an increase in pressure?
The equilibrium shifts to the side with less molecules.
According to Le Chatelier, what happens to equilibrium when there is an decrease in pressure?
The equilibrium shifts to the side with more molecules.
What happens when the pressure is doubled?
The concentration is doubled as well.
What happens to the progress of a reaction when the pressure changes, but the number of moles of gas in the reactants and products are the same? (Or if there is no gas present)
There is no effect on the progress of a reaction.
Why is the change in temperature ‘pseudo le chatelier?’
Because it results in a new equilibrium value, not the same value.
What happens when a reaction at equilibrium is heated for an endothermic reaction? Hint: heat + reactants –> products
Increase in products, rate of reaction to products is faster so k increases.
What happens when a reaction at equilibrium is heated for an exothermic reaction? Hint: reactants –> products + heat
Increase in reactants, rate of reaction to reactants is faster so k decreases.
What is the equilibrium constant in the opposite direction?
The equilibrium constant in one direction is the inverse of that in the opposite direction. K’(c) = 1/K(c) or K’(p) = 1/K’(p)
What happens with the equilibrium when the reaction occurs in the presence of a catalyst?
A catalyst increases the rate of the reaction by making a lower-energy pathway available for both forward and reverse reactions, equilibrium is achieved quickly but there is no change in equilibrium position.
How do you calculate K when reactions are added together?
Multiply their respective K values together to get a new K value.
Do Acids accept or donate protons?
Acids are proton donors, add protons to base
Do bases accept or donate protons?
Bases accept protons from acids
Water is referred to as amphiprotic, what does this mean?
It can donate and accept protons
What does amphoteric mean?
Water and compounds that can react with both acids and bases
What is the conjugate base?
The compound that forms from the acid.
What is the conjugate acid?
The compound that forms from the base.
How can pH be expressed logarithmically?
pH = -log[H3O+] or 10^(-pH) = [H3O+]
How can pOH be expressed logarithmically?
pOH =-log[OH-] or 10^(-pOH) = [OH-]
What does pKw = ?
14 = pH + pOH in any aq. solution at 25C
What are the requirements for a strong acid?
The ionization reaction is complete in water and there is no equilibrium arrow present. All strong acids have equal strength, but not necessarily pH.
List the 6 Strong Acids as compounds.
HClO4, H2SO4, HNO3, HBr, HI, HCl
List the 6 Strong Acids with their names.
Perchloric Acid (HClO4), Sulfuric Acid (H2SO4), Nitric Acid (HNO3), Hydrobromic Acid (HBr), Hydroiodic Acid (HI), Hydrochloric Acid (HCl)
What are the requirements for a strong base?
The dissociation reaction is complete in water (reacts with H2O but dissociates), no equilibrium arrow. They are all salts of metals (alkali and earth).
List the 6 Strong Bases as compounds.
LiOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2, NaOH
List the 6 Strong Bases with their names.
Lithium Hydroxide (LiOH), Potassium Hydroxide (KOH), Calcium Hydroxide (Ca(OH)2), Strontium Hydroxide (Sr(OH)2), Barium Hydroxide (Ba(OH)2), Sodium Hydroxide (NaOH).`
How are weak acids different than strong acids?
They are not at equal strength and their reaction does not go to completion (equilibrium). They partially ionize in aq. solutions to reach equilibrium.
What happens when the equilibrium acid-ionization constant Ka increases?
As Ka increases, so does the strength of the weak acid because pKa decreases. The lower the pKa, the stronger the acid.
How are weak bases different than strong bases?
They partially ionize in aq. solutions to establish equilibrium and react with H2O unlike strong bases.
What happens when the equilibrium base-ionization constant Kb increases?
As Kb increases, so does the strength of the weak base because pKb decreases. The lower the pKb, the stronger the base.
What is the weak acid equation?
[H3O+] = sqrt.Ka[HAinitial]
What is percent ionization for acids?
[H3O+]/[HAinital] * 100
What is percent ionization for bases?
[OH-]/[BOHinitial] * 100
How does higher values of Ka or Kb affect percent ionization?
Higher Ka & Kb = higher percent ionization.
How are the relative strengths of conjugate acid-base pairs related?
Stronger acids have weaker conjugate bases and weaker acids have stronger conjugate bases.
What is the Kw equilibrium constant equal to in terms of Ka and Kb?
Kw = Ka * Kb
How does the acidity or basicity of a solution change in the presence of salts?
Salts like NaCl dissolve in water and dissociate into their ions. Acidity/basicity of solution depends on relative acidity and basicity of ions based on their conjugate acids and bases. For instance, the conjugate of Na+ is a strong base NaOH so Na+ is a very very weak conjugate acid and Cl- is the very weak conjugate base of a strong acid HCl. Thus NaCl will not affect the pH of a solution.
What are polyprotic acids and bases?
Acids/bases that accept more than one proton or donate more than one proton. Generally, the first Ka/b is bigger than the second Ka/b so acidity/basicity is determined by the first Ka/b.
What happens to natural waters as the amount of CO2 increases?
the concentration of CO2(aq) in water increases so the concentration of carbonic acid and concentration of hydronium ions decreases - pH decreases and acidity increases.
What are buffer solutions?
Buffer solutions make small pH changes when concentrated strong acids or bases are added to them. They contain similar concentrations of a weak acid and a salt of its conjugate base or similar concentrations of a weak base and a salt of its conjugate acid. [HA] (weak base) ~ [A-] (conjugate acid).
What is the Henderson-Hasselbalch Equation for buffers?
pH = pKa + log([A-]/[HA]), aka pKa + log(Ka)
What is the buffer capacity?
The amt of strong acid/base added to a buffer solution will be buffered as long as the pH does not change more than +/- 1 unit.
Examples of buffers in human body.
Phosphate system for intracellular fluid, ammonia/phosphate system in urine
