1. Explain the nature of the equilibrium constant, define various variations of the equilibrium constant, and write an equilibrium expression for a reaction or Law of Mass Action.
2. Calculate the value of the equilibrium constant using the Law of Mass Action.
3. Define entropy and and enthalpy.
4. Explain how changes in entropy relate to a change of state, a change in temperature, and a change in the number of product particles compared with the reactant particles.
5. Define Gibbs Free Energy, state the equation for Gibbs Free Energy, and examine various combinations of entropy and enthalpy that lead to a spontaneous reaction.
Here is a brief video providing a quick overview for defining equilibrium and writing a Law of Mass Action (or equilibrium expression):
The concentration values are in Molarity (M), but the units are not included in the expression. This is one of the few instances where the units are not included in the calculation. The brackets around the number, e.g. [0.5], are used for molar solutions.
Pure liquids or solids, even though they may be in a reaction, are not included in the equilibrium expression.
By the way, Keq is typically a general abbreviation for an equilibrium expression, but sometimes a slightly different symbol is used -- it's still the equilibrium expression but specific to water, Kw, acids, Ka, bases, Kb, and Ksp for solubility product.
This page is a nice overview of the equilibrium expression variations as well is calculating Kp:
Here's one worksheet to practice writing Keq expressions:
Using this equilibrium expression, values for the substance concentrations can be calculated or used to determine Keq. The following video (10 minutes) but shows a few examples using the ICE method. ICE is I for initial concentration, C for change in concentration, and E for equilibrium concentration.
I may have mentioned enthalpy and entropy in previous entries, but I'm going a little more in-depths here -- enthalpy, or heat content, is represented by delta H -- it can only be measured by the release of energy -- calorimetry is the accurate and precise measurement of heat change for chemical and physical properties.
Entropy is the disorder of a system. The law of disorder states that processes move in the direction of maximum disorder or randomness. An easy to remember example is that of a bedroom starting cleaned and orderly and eventually getting messy and disordered, not to return to a state of order unless energy is exerted.
The natural tendency in the universe is to a state of lower energy (negative delta H) and higher entropy (positive delta S).
Here is a brief overview of enthalpy (delta H) -- the narrator later gets into adding reactions to get an overall delta H value -- Hess' Law states that if you add two or more thermochemical equations to give a final equation, then you can also add the heats of reaction to give the final heat of reaction -- a few examples are solved in this video as well. Not all introductory courses get into Hess' Law problems, so use your discretion about covering it. If it's not in the course syllabus and you cover it, there might be complaints.
This page contains multiple-choice questions and answers:
Here is another worksheet:
The topics of enthalpy, entropy and Gibb's Free Energy can be covered during a thermodynamics unit. Calorimetry labs are typical during this coverage -- I have a Calorimetry lab in my book "Chemistry on a Budget."
The National Science Teacher Association (NSTA ) annual conference was this past week in Boston, Massachusetts. If you attended the convention, please write me about it!
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Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired!
Have a good week!