Lecture 4 Flashcards
(25 cards)
What happens if more A is added to a system at equilibrium?
If more A is added, Q < K → equilibrium position moves to the right, reducing [A] and increasing [B] until equilibrium is again reached.
Example: Q = K
What happens if some A is removed from a system at equilibrium?
If some A is removed, Q > K → equilibrium position moves to the left, increasing [A] and decreasing [B] until equilibrium is again reached.
Example: Q = K
How does adding PCl(g) affect the equilibrium position?
Adding PCl(g) will instantaneously decrease Q, and the system will no longer be at equilibrium. To return to equilibrium, Q must increase, which can be done by making more PCl and using up Cl. The equilibrium position will move to the right.
How can pressure be changed in a system?
Pressure can be changed by changing volume or by adding an inert gas.
What is the relationship between Q and volume?
Qc is proportional to 1/V. Thus, if V increases, Qc decreases. If volume increases, Q < K and the equilibrium position will move to the right.
What happens when changing pressure in a system with equal moles of gas on both sides?
Changing the pressure by changing the volume will have no effect on equilibrium, as the volume terms cancel out in the expression for Q.
Does adding an inert gas affect the position of equilibrium?
Adding an inert gas (e.g., helium) will have no effect on the position of equilibrium, as there is no term for the inert gas in the expression for Q.
What is solubility?
Solubility (s) is a measure of how much solute will dissolve in a given volume of solvent.
What is a saturated solution?
A saturated solution is formed when the maximum amount of solute is dissolved in a particular volume of solvent at temperature T.
What factors affect solubility?
Solubility depends on the chemical nature of solute and solvent, temperature (T), and pressure (p) for gaseous solutes.
How much NaCl can dissolve in water at 25 °C?
Can dissolve 35.9 g NaCl in 100 mL water at 25 °C. We say that NaCl is soluble in water.
How much AgCl can dissolve in water at 25 °C?
Can only dissolve 0.00019 g AgCl in 100 mL water at 25 °C. AgCl is considered insoluble in water, but it is slightly (sparingly) soluble.
What is Ksp?
Ksp, the Solubility Product, is the equilibrium constant for the dissolution of a slightly soluble salt in water.
What is the equilibrium expression for the dissolution of AgCl?
The equilibrium for the dissolution of AgCl(s) is written as the products of the ions, each raised to the power of their stoichiometric coefficients.
Pure solids do not appear in an equilibrium constant expression.
Do equilibrium constants have units?
No, equilibrium constants have no units.
What is the relationship between Ksp and solubility (s)?
You can derive a relationship between Ksp and s by following these steps:
1. Write the expression for Ksp.
2. Express the concentration of ions in terms of s.
3. Substitute (2) into (1).
What does the solubility (s) represent?
The solubility is equal to the amount of solid that can dissolve in 1L of water.
What is the Ksp expression for AgCl?
Ksp = [Ag+][Cl-]
If s moles of AgCl(s) dissolve, there will be s moles each of Ag+ and Cl-.
How do you calculate s from Ksp for BaSO4?
For BaSO4, Ksp = [Ba2+][SO4^2-]. Given Ksp = 1.1 × 10^-10, you can calculate s.
What is the solubility of BaSO4 in water?
s = 1.0 × 10^-5 mol L^-1
This is based on Ksp = 1.1 × 10^-10.
What does EPA recommend for Ba2+ concentration in drinking water?
[Ba2+] < 1.46 × 10^-5 mol L^-1 (< 2 mg L^-1).
How can you determine if a precipitate will form?
Compare Qsp and Ksp:
- If Qsp < Ksp, no precipitate will form.
- If Qsp > Ksp, precipitation will occur.
What is Qsp?
Qsp is sometimes called the ionic product.
