8. Equilibrium Flashcards
Define equilibrium.
At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction, and thus, no changes in concentration are observed (although forward and reverse reactions are constantly occurring).
What is the equilibrium constant? What is the equilibrium expression?
Keq = [products]^x / [reactants]^y
x and y are stoichiometric coefficients.
At a given temperature, any reaction will proceed towards its equilibrium concentrations of product and reactant. Using the above equation, we can find the equilibrium constant.
Pure liquids and solids are not included in the equilibrium expression because their concentrations cannot change. If have gases, we use partial pressures instead of concentrations.
t or f, the equilibrium constant changes with temperature.
true, therefore, Keq is only a constant for a given temperature.
Explain
K = 1
K > 1
K < 1
K = 1 indicates that [R] = [P] at equilibrium
K > 1 indicates that products are favored at equilibrium
K < 1 indicates that reactants are favored at equilibrium
t or f, Keq can be negative.
False, Keq can only be positive
concentrations cannot be negative
What is the reaction quotient (Q)?
At a given temperature, the [R] and [P] are governed by their Keq. However, in real world situations, the concentrations may be anything (i.e. not actually at equilibrium concentrations). The reaction quotient is the equilibrium expression using the given concentrations (not eq concentrations).
Explain
Q = K
Q > K
Q < K
Q = K, then the concentrations are at equilibrium.
Q > K, products are currently favored, and the reaction will shift to the left to find equilibrium.
Q < K, reactants are currently favored, and the reaction will shift to the right to find equilibrium
What is Le Chateliers principle?
The principle explains that a system at equilibrium will try to restore equilibrium if any changes are imposed on that system. The most common situation is adding or removing reactants or products.
If we add reactant, the system will want to consume that reactant to return to equilibrium concentrations (right shift).
N2 (g) + 3H2 (g) 2NH3 (g) + heat
Explain what happens if you decrease the volume this reaction takes place in.
Recall for gaseous reactions, we use partial pressures instead of []’s. If volume decreases, then pressure will increase. To help restore equilibrium, the reaction must shift to the side with LESS moles (to try reduce pressure).
N2 (g) + 3H2 (g) 2NH3 (g) + heat
So V decreases, P increases, the reaction will shift to the products. If volume increases, the opposite would occur to try maintain pressure.
N2 (g) + 3H2 (g) 2NH3 (g) + heat
Explain what happens if you increased the temperature of the reaction.
heat is written on the products side, thus, this reaction releases heat (exothermic). Similar to []’s, if we add heat (increase temperature), the reaction will shift to the left to try and restore equilibrium.
Note: unlike changing pressure or []’s, changing temperature will affect a reactions Keq.
t or f, Le Chateliers principle only applies to reactions that are already in equilibrium.
true! for example, all reactions proceed faster with increased temperature. For an exothermic reaction with no products formed, increased temperature will make the forward reaction go faster (collision theory). Once at equilibrium the increased T will encourage the reverse reaction.
What happens if you add an inert gas to a system that is held at constant pressure?
The added gas will cause volume to increase which effectively reduces the partial pressures of the system. If their partial pressures have been reduced, the system will shift to the side with more moles.
What happens if you add an inert gas to a system that is held at constant volume?
The added gas has no effect, unlike if you add an inert gas to a system that is held at constant pressure
How does a catalyst affect equilibrium?
A catalyst has no effect at equilibrium as it increases the forward and reverse reactions equally.
What is solvation? What is hydration?
When a solute is dissolved (dissolution) in a solvent. solvation is when the solvent fully surrounds the solute. When this occurs with water, it is hydration.
t or f, a solid inside another solid is a solution.
True (alloy)
How can you predict, in general, what solutes will dissolve in a given solvent?
Like dissolves like.
solutes will dissolve in a solvent if the IMF’s being broken are replaced with equal or stronger IMF’s between the solute and solvent.
What is the van’t Hoff factor (i)?
The van’t Hoff factor explains how many ions a given unit of a compound will dissociate into.
glucose, i = 1
NaCl, i = 2
CaCl2, i = 3
What is a strong electrolyte? Ionic compounds verses covalent compounds?
If a compound dissociates completely (100%) it has more ions in solution and is called a strong electrolyte. All ionic compounds are strong electrolytes.
What is a saturated solution, molar solubility, and precipitation?
A solutes molar solubility is the maximum amount of solute (in moles) a solvent can dissolve. At this point the solution is saturated because no more solute can dissolve.
Added solute will precipitate out of solution.
At saturation, dissolution and precipitation work against each other in dynamic equilibrium.
What are the three phase solubility rules, with regards to temperature and pressure?
- solids in liquids
- gases in liquids
- gases in liquids
- the solubility of solids in liquids increases with increasing temperature
- the solubility of gases in liquids decreases with increasing temperature
- the solubility of gases in liquids increases with increasing pressure
What are the three salt solubility rules in water?
- group 1 salts
- Nitrates, etc.
- Silver, etc.
- All group 1 salts (Li+, Na+, etc.) and ammonia salts (NH4+) are soluble in water
- All nitrate (NO3-), perchlorate (CLO4-), and acetate (methyl-COO-) salts are soluble
- All silver, lead, and mercury salts are insoluble, EXCEPT if they are paired with any anion in section 2.
What is the solubility product (Ksp)?
Ka, Kb, Ksp, Kp are all forms of the equilibrium constant in different situations. The solubility product explains the extent a salt dissociates (similar to how Ka explains the extent an acid dissociates).
Remember: pure solids and liquids are not included in the reaction.
t or f, at equilibrium, a solution is saturated.
true: precipitation = dissolution
The ion product (Qsp) is the reaction quotient for solubility problems that are not at equilibrium (i.e. saturated). Explain,
Q = K
Q > K
Q < K
Q = K, at equilibrium / saturation
Q > K, products are currently favored so the system will precipitate
Q < K, reactants are currently favored, so the system will dissolve more solute
What is the common ion effect?
We can alter the solubility of one salt by adding another salt.
MgOH –> Mg + OH
If we now add NaOH into solution, we increase the concentration of OH ions. By Le-Chateliers principle, the above reaction will try consume some OH, shifting the reaction to the left.
Thus, adding a common ion decreased the solubility of the slightly soluble salt, MgOH.
What is a complex ion? What do they do?
Complex ions are typically metal ions surrounded by 2, 4, or 6 ligands. Opposite to the common ion effect, the addition of certain species can increase the solubility of an already dissolved salt, by forming a complex ion.
AgCl –> Ag + Cl
add ammonia
Ag(NH3)2 forms, which is very soluble
What is a chelating agent?
A chelating agent is a chemical compound that reacts with metallic ions to make them more soluble in water (i.e. formation of complex ions)
When ΔG = 0, a reaction is at equilibrium (K = Q)
How is ΔG related to the reaction quotient (Q)?
ΔG = ΔG° + RTlnQ
If at equilibrium then ΔG = 0, and ΔG° = -RTlnK
Explain the difference between ΔG and ΔG°.
ΔG = the free energy of a given situation where the products and reactants are at random []’s = Q. This describes the spontaneity of a reaction. The reaction will proceed until it reaches equilibrium.
ΔG° = the free energy at standard conditions. This explains the relative proportions of products to reactants at equilibrium
Explain
ΔG° = 0
ΔG° > 0
ΔG° < 0
ΔG° = 0, K = 1, products and reactants are at roughly equal amounts at equilibrium
ΔG° > 0, at equilibrium, reactants are favored
ΔG° < 0, at equilibrium, products are favored
