CITATIONS

http://chem102-leegroup.blogspot.com/

(I used this website for a quick equilibrium summary)

http://dictionary.com

(I used this website for the important definitions I posted)

http://www.google.com/images

(I used google images for all the images I put on my blog)

EQUILIBRIUM SUMMARY

1. Equilibrium has been reached when concentrations no longer change over time.
2. The equilibrium constant of a reaction in the reverse direction is the inverse of the equilibrium constant of the reaction in the forward direction
3. The equilibrium constant of a reaction that has been multiplied by a number is the equilibrium constant of the reaction raised to a power equal to that number
4. The equilibrium constant for a net reaction made up of two or more steps is the product of the equilibrium constants for the individual stepsIf K >> 1 (big) then equilibrium lies to the right (products)
5. If K <<>
6. Leave solids and pure liquids out of equilibrium expressions, the concentration of these substances does not change with time.
7. Calculating Equilibrium Constants; is easy when we know all the equilibrium concentrations (or pressures), a balanced equation, and can write a rate expression.
8. When we know initial concentrations and an equilibrium concentration, use the stoichiometric coefficients to predict the change in concentrations.U se the Initial, Change, Equilibrium (ICE) procedure to find all the equilibrium concentrations and sub these values into the equilibrium expression
9. Calculating Equilibrium Concentrations; when we know K and all the initial concentrations only, use the ICE procedure and solve for x the change in concentration, possibly by solving a quadratic function.

Click on any of the links below for online quizzes on different aspects of equilibrium!

http://library.thinkquest.org/C006669/data/Chem/quizzes/equilibrium.html

http://lrc-srvr.mps.ohio-state.edu/under/chemed/qbank/quiz/bank11.htm

http://www.sciencegeek.net/Activities/lechatelier.html

http://www.sciencegeek.net/Activities/equilcalcconc.html

http://www.sciencegeek.net/Activities/calcK.html

This science teacher has posted videos on Youtube, reviewing everything that we have learned this year, including equilibrium, kinetics, bonding, stoichiometry, atomic theory, the mole, acids and bases, redox, and energetics. His reviews are short and easy to follow! The link below will take you to the 100 videos he has posted so far: you will have to look through them for the equilibrium videos (on page 4), or watch all of them.

http://www.youtube.com/view_play_list?p=959A532E49F9F95C&page=1

LeCHATELIER'S PRINCIPLE

"If a change is made to the conditions of chemical equilibrium, then the position of the equilibrium will readjust to minimize made."

1. Concentration
   - If you increase the concentration, the equilibrium will shift away from that increase in the opposite direction.
   - If you decrease concentration, equilibrium will shift toward the decrease.
   
2. Pressure
   - If you increase the pressure, equilibrium shifts to the side with the fewest moles of gas.
   - If you decrease the pressure, equilibrium shifts to the side with the most moles of gas.
   
3. Temperature
   - an increase in temperature shifts in the endothermic direction.
   - a decrease in temperature shifts in the exothermic direction.
   -note that temperature also affects the Kc values.
   
   
   
   
   Go to http://www.youtube.com/watch?v=Ywzvzw6Rdpk for a video on LeChatelier's Principle!
   
   Go to http://ths.sps.lane.edu/chemweb/unit11/problems/eq/ for an online quiz on LeChatelier's Principle!
   
   
   

THE EQUILIBRIUM CONSTANT (Kc)

1. The equilibrium constant does not have fixed units.


2. Concentrations of certain substances remain constant... so they are not included in the equilibrium equation. Solids have a constant concentration and a fixed density... so they are omitted. The concentration of water is also taken as a constant in aqueous solutions.
   
3. Coefficients in this equation are represented by raised powers.
   
   4NH3 + 5O2 ↔ 4NO + 6H2O
   
   Kc = ([NO]^4)([H2O]^6)/([NH3]^4)([O2]^5)
   



4. Because forward and reverse constants never change at a given temperature, their ratio will always give the same value at equilibrium. This is known as the equilibrium constant.

Kf[A][B] = Kr[C][D]

Therefore:

Kf/Kr = [C][D]/[A][B]

OR

Kc = [C][D]/[A][B]

**What can Kc values tell us?

1. If Kc is very large, the reaction goes to completion.
2. If Kc is less than 1, it will not go to completion and may be an equilibrium reaction.
3. If Kc is very small, the reaction may not occur at all.
   
   Go to http://www.geocities.com/junebug_sophia/equilConst.htm for an online Equilibrium Constant quiz!

DETERMINATION OF RATE

The rate of reaction is determined by the rate constant (K) multiplied by the concentration of either the products or the reactants.

A + B ↔ C + D

Rate Determination

Forward Rate = Kf[A][B]
Reverse Rate = Kr[A][B]

**Remember that the [ ] symbols represent concentration!

In equilibrium, the forward rate equals the reverse rate.

Kf[A][B] = Kr[A][B]

TYPES OF EQUILIBRIUM

There are three main types of equilibrium: chemical equilibrium, phase equilibrium, and solution equilibrium.

1. Chemical Equilibrium
   
   As in the previous examples, the products of a reaction can go in reverse, creating an equaling out of products and reactants.
   Go to http://www.youtube.com/watch?v=sjkuUUf-DJM for a video on chemical equilibrium!
   
   
2. Phase Equilibrium
   
   Phase equilibrium exists between the solid and liquid phase of a substance. It is the point at which both the liquid and the slid exist at the same time, for example, ice in water. This occurs at the melting/freezing point.
   
   
3. Solution Equilibrium
   
   Solution equilibrium is when both the dissolved solute and the re-crystallized form are present, for example, sugar in water. This occurs at the point of saturation.
   

RATES OF EQUILIBRIUM REACTIONS

1. Forward reactions occur first because no products have formed yet.
   
2. As products form, they may again react to form initial reactants. When the rate of the products forming equals the rates the reactants are re-forming, the system is in a state of dynamic equilibrium.
   
3. In essence, forward reactions occur more quickly in the beginning to form products.
   
4. Reverse reactions start off slowly because they must wait for products to form.
   
5. Eventually, both the forward and reverse reactions equal out.
   
6. The Effect of Surface Area on Reactions: The more finely divided the solid is, the faster the reaction happens. A powdered solid will normally produce a faster reaction than if the same mass is present as a single lump.
   **(Go to http://www.youtube.com/watch?v=srKewy69Pdk for a video on how SURFACE AREA affects the rate of reaction!)
   
   



7. The Effect of Concentration on Reactions: As the concentration of the reactions decreases, the forward reaction slows. As the concentration of the products increase, the reverse reaction speeds up.
   **(Go to http://www.youtube.com/watch?v=srKewy69Pdk for a video on how SURFACE AREA affects the rate of reaction!)
   
8. The Effect of Temperature on Reactions: As you increase the temperature the rate of reaction increases. As a rough approximation, for many reactions happening at around room temperature, the rate of reaction doubles for every 10°C rise in temperature.
   **(Go to http://www.youtube.com/watch?v=0XQVXFL4uoo for a video on how TEMPERATURE affects the rate of reaction!)
   
   


9. Eventually the rates of reaction for the forward and the reverse process equal out!

**Example:

CH4 + H2O ⇌ 3H2 + CO

(In this reaction, as the CH4 and water get "used up," more products form and the forward reaction slows. As the products form, there is now the potential for the reverse reaction. As more and more product form - meaning, as the concentration of product increases - the reverse reaction speeds up.