Init: 4/20/2009 by Daniel Raymond Barnes

EQUILIBRIUM Init: 4/20/2009 by Daniel Raymond Barnes

S.W.B.A.T. . . . . . . Explain how reversible reactions result in equilibrium.

Please open your textbooks to page 549. 2SO2(g) + O2(g) ↔ 2SO3(g) How would you translate this into English? “Sulfur dioxide gas reacts reversibly with oxygen gas to form sulfur trioxide gas.” You could just as truthfully say, “Sulfur trioxide decomposes reversibly into sulfur dioxide and oxygen gas.”

2SO2(g) + O2(g) ↔ 2SO3(g) Let’s say you have an airtight, rigid cannister of pure sulfur trioxide gas. According to the above equation, sulfur trioxide turns into . . . sulfur dioxide gas and oxygen gas.

2SO2(g) + O2(g) ↔ 2SO3(g) Let’s say you have an airtight, rigid cannister of pure sulfur trioxide gas. According to the above equation, sulfur trioxide turns into . . . sulfur dioxide gas and oxygen gas. The amount of SO3 starts out high . . . . . . But then immediately begins to fall because of SO3 turning into SO2 & O2. SO3 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) At first, the rate of SO3 turning into SO2 & O2 is very high because, at first, the concentration of SO3 is very high. Notice the slope of the line. It’s a pretty steep, downward slope. As the reaction proceeds, there is less and less SO3 left, so the reaction rate slows down. Notice the slope of the line. SO3 Concentration Not quite as steep, is it? Time

2SO2(g) + O2(g) ↔ 2SO3(g) As more and more SO3 turns into SO2 & O2, the rate of SO3 disappearing slows down . . . . . . and eventually reaches zero. When the amount of SO3 stops changing, the graph becomes horizontal. SO3 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) The reason the SO3 graph goes horizontal is because at some point, there is so much SO2 & O2 and so little SO3 that the rate at which SO2 & O2 turn back into SO3 is just as fast as the rate at which SO3 turns into SO2 & O2. SO3 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) When opposite processes occur at the same rate, their effects cancel each other out, and the amounts of things remain constant. When opposite processes occur at the same rate in a system, the system is said to be in a state of “equlibrium”. SO3 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) Let’s re-run the animation, but this time also graph the amount of sulfur dioxide gas and oxygen gas. SO3 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) At first, there are 10 moles of SO3 . . . Zero moles of SO2, and . . . Zero moles of O2. During the first hour, four SO3’s turn into . . . . . . four SO2’s and two O2’s Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) At first, there are 10 moles of SO3 . . . Zero moles of SO2, and . . . Zero moles of O2. During the first hour, four SO3’s turn into . . . . . . four SO2’s and two O2’s During the next two hours, two SO3’s turn into . . . . . . two SO2’s and one O2 Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) Another two moles of SO3 turn into two moles of SO2 one mole of O2, but it takes a much longer time. Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) Another two moles of SO3 graph turn into two moles of SO2 one mole of O2, but it takes a much longer time. At that point, the system has reached equilibrium and the amounts of the chemicals stop changing. Concentration Time

2SO2(g) + O2(g) ↔ 2SO3(g) A WORD OF CAUTION: At equilibrium, the forward reaction rate equals the reverse reaction rate. BUT The amounts of the chemicals do NOT equal each other. They’ve just stopped changing. Concentration Time

Chemical Equilibrium is DYNAMIC What does this mean?

DYNAMIC is the opposite of static

Statues are static. They don’t do anything. They don’t move. They don’t talk.

Living things are dynamic.

Systems of living things are dynamic, too. Let’s look at an example of a system of living things in “dynamic equilibrium”

Imagine a town where there are 100 marriages every year . . . This town is in a state of “dynamic equilibrium” with regard to marriage. Stuff is happening. The system is not static. . . . and 100 divorces every year. If the number of marriages equals the number of divorces, then the two processes cancel each other out and the number of married couples remains constant.

Consider the reversible decomposition of carbonic acid into carbon dioxide and water. This happens in your blood, and also in soda, beer, champagne, and other “carbonated” beverages. water carbonic acid carbon dioxide

There’s stuff going on here, isn’t there? It’s not static. It’s “dynamic”. Carbonic acid is forming in one place, and decomposing in another. These opposite processes cancel each other out, so the amounts of carbonic acid, carbon dioxide, and water remain constant.

[virtual school project has a good equlibrium video Includes hole filling/hole digging example, etc.]

If the force of gravity is equal and opposite to the force created by a vehicle’s engine, the vehicle will be in a state of equlibrium and will not accelerate upward or downward. Vertical velocity will be constant, maybe even zero, which would cause the vehicle to hover in place, motionless. PHYSICS!

EARTH SCIENCE!

S.W.B.A.T. . . . . . . Predict the outcome of disturbing a system that is in equilibrium

LeChatelier’s principle, according to Wikipedia [snicker]: “If a chemical system at equilibrium experiences a change in concentration, temperature or total pressure, the equilibrium will shift in order to minimize that change.” Henry Louis Le Châtelier (October 8th 1850 - September 17th 1936) http://www.howjsay.com/index.php?word=le+Chatelier LeChatelier’s Principle is a chemical shock absorber that helps make life possible. It helps prevent extremes by opposing change.

Some lingo . . . If we say that disturbing an equlibrium “shifts the equilibrium to the left”, this means that the system responds to the disturbance by increasing the amount of reactants and decreasing the amount of products. A + B  C + D If we say that disturbing an equlibrium “shifts the equilibrium to the right”, this means that the system responds to the disturbance by increasing the amount of products and decreasing the amount of reactants. A + B  C + D

Download & run the “reactions & rates” simulation. http://phet.colorado.edu/en/simulations/category/chemistry/general

Mr. Barnes’ LeChatelier’s PrincipleWorksheet ¿Porque? Porque es bonito

I hate this question. I’m deactivating it. It’s a CST reject.

NO2(g)  N2O4(g) + heat

Nitrogen dioxide-rich smog in Sao Paolo, Brazil

How many gas molecules on each side? No gas on the left Two gas molecules on the right System tries to raise the pressure back up again by . . . . . . increasing the number of gas molecules by . . . . . . shifting the equilibrium to the right.

Here’s a link for a YouTube video about the Haber process. It’s one of the most important industrial processes in the world. It’s a great example of how understanding how pressure, temperature, concentration, and catalysts affect reaction rates can help people make useful stuff. This process, by some estimates, creates one third of the food eaten by the human race. That means it, alone, increases human population on the planet 50%, if I’ve interpreted it right. Without it, one out of every three people couldn’t exist. It may smell awful, but, Indirectly, ammonia feeds a LOT of people. Fritz Haber 1868-1934 http://www.youtube.com/watch?v=c4BmmcuXMu8 3H2 + N2 2NH3

Please pardon our mess. All of my PowerPoint presentations are eternal works-in-progress, but this one is espcially incomplete. Sorry.

Lesson Sketch Definition of equilibrium opposite processes occur at equal rates effects cancel amounts problably NOT equal; rates are equal dynamic, not static; effects cancel, but plenty of activity balance, stability; amounts of chemicals remain constant Non-chemical examples marriage/divorce income/expenses mortality/natality gravity/lift immigration/emmigration LeChatelier’s Principle: definition Example problems Concentration changes Temperature changes Pressure changes Non-effect (!) of catalysts – same eq pos, just reached faster Applications in industry

Init: 4/20/2009 by Daniel Raymond Barnes