ChemStd 9a: Le Chatelier's Principle

First of all, what is Le Chatelier's principle? If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

In essence, whatever is added to the equation or shifts the equilibrium, Le Chantelier's principle states that the equation will automatically shift to counter this change and maintain an equilibrium; it will do exactly the opposite of whatever is disrupting the equilibrium.

• Effect of the change in concentration:

CO + 2 H₂ ⇌ CH₃OH

If more CO was added, then according to Le Chantelier's principle, the amount of CH₃OH would increase also. Whenever there is a change in concentration, the opposite side of the equation will experience a similar change, whether a decrease or increase of molecules.

• Effect of the change in temperature:

N₂ + 3 H₂ ⇌ 2 NH₃ + 92kJ

In the above equation, it shows heat is part of the product, making this an exothermic reaction. If the temperature increases, the equilibrium will shift to the side that does not have heat to create a balance and decrease the temperature, which is to the left. Decreasing the temperature will shift the equilibrium left, towards the reactant.

H₂(g) +I₂(s) + 52 kJ ⇌ 2HI(g)

In this equation, heat is part of the reactant, making this an endothermic reaction. Increasing the temperature will cause shift the equilibrium right, however, decreasing the temperature, shifts the equilibrium toward the left to balance the equation at a constant temperature.

• Effect of the change in pressure:

2NO₂(g) ⇌ N₂O₄(g)
An increase in pressure results in a shift towards the side with the least molecules, which is N₂O_{4. A decrease in pressure however causes the equilibrium to shift to the side with more molecules to counter the decrease in molecules and maintain an equilibrium; in this case} 2NO_2.

For a full complete explanation of Le Chantelier's Principle:
http://www.youtube.com/watch?v=Ywzvzw6Rdpk

Rock Candy!! (a chemistry mini project)

How to make rock candy...

You need:
-sugar
-water
-spoon (to mix the sugar and water solution
-hot plate (to heat the sugar and water solution)
-life saver candy
-string
-Popsicle stick
-beaker or jar

Procedure:
-mix sugar and water together and heat at a high temperature until the sugar is dissolved.
-take the string, tie one end to the Popsicle stick and the other end to the life saver (through the hole in the candy)
-coat the hanging string with the life saver with dry sugar.
-pour the sugar and water mixture into the jar or beaker.
-balance the Popsicle stick on top of the jar so the life saver hangs down but DOES NOT touch the bottom of the jar.
-wait, and watch, you should see some crystals that grow in a 3-7 days!

The science of crystals:
Precipitation: The sugar and water solution is supersaturated, meaning there is more solute (sugar) than water. A supersaturated solution is unstable and so the solute is pushed out from the solution and a precipitate forms.

Evaporation: as days past, the water slowly evaporates from the solution, making it more saturated, which forces more sugar to cling to the string. The crystals slowly build on each other until you eventually have your rock candy.

Photo credit: Rachel Kawawaki!!

USMAIL (say it fast and it sounds like U SMELL) (a chemistry mini project)

Smells, when I think of them I automatically think of the chocolate factory by our school and how during brunch we can smell the delicious chocolate that wafts over the school walls. But what makes it so you can smell the smell of fresh baked cookies in the living room, or the odor of the porter potty down the street. It's all due to diffusion.

It was mother's day on Sunday and my cousin brought these beautiful pink roses for the mothers in our family. They were put in a vase and after a while, we sat down to watch the Suns vs Spurs game and after a while, I started to notice this lovely flowery scent. It smelled really nice, but I wondered how I could smell it from all the way across the room!

Molecules naturally move from a high concentration to a low concentration. Since the smell of the flowers were highly concentrated in one part of the air, the smell (molecules) would gradually mix with the unscented molecules to try and create an equilibrium. This is why a scented candle makes the whole room smell nice.

Another experiment you could try with this is simply:
1. spray a febreze bottle into the air
2. wait for a while then see if you could smell the scent.
3. have several people with you, one in front of the other, so that you can see the gradual diffusion of the molecules over a period of time. (the person closest to the sprayed molecules should smell the scent first, gradually working back to the person furthest away.)

Photo credit: my dad!

Lets Make Play Dough!!! (a chemistry mini project)

In class we made play dough using:
- 1 teaspoon of oil
- 1 cup of flour
- 1 cup of sugar
- 1 cups of water
- couple drops of food coloring

We mixed all of together at high heat and stir the mixture until in becomes more puddy and manageable and then we took it out, coated it with flour to not make it so sticky and then presto, you have play dough!! Now you can make whatever shapes you want with it, a star, a heart, one guy even made a mini tank!!

The chemistry behind it:
Flour is held together by hydrogen bonds, however, using the sugar we were able to transform the molecular structure and cut the hydrogen bonds, creating the dough's new texture of play dough.

Photo credit: Rachel Kawawaki! :)

Brownies anyone?? (a chemistry mini project)

So for my mini chem project, I decided to make brownies!!! What's so scientific about brownies you say? Well here's the answer (according the the various websites I researched):

- Flour is used to make the bread or whatever you're baking to supports the ingredients as it rises. In the case of bread, CO2 bubbles are released to make the bread light and airy.
- Sugar is almost like a catalyst, it feeds the yeast, causing the CO2 reaction to happen faster.
- Baking Soda forms CO2 in this equation: NaHCO3 + H+ → Na+ + H2O + CO2.
- Eggs are used to keep the CO2 from escaping too soon and also to bind the ingredients together.
- Fat (butter) gives what you are baking a lighter texture.
- Why so much talk about CO2? It's because CO2 helps the dough rise, and that's definitely important when it comes to talking about bread!

So anyways, here's the ingredients for the brownies I made (based off of Food Networks' Ina Garten):
- 1 pound unsalted butter
- 1 pound plus 12 ounces semisweet chocolate chips, divided
- 6 ounces unsweetened chocolate
- 6 extra-large eggs
- 2 tablespoons pure vanilla extract
- 2 1/4 cups sugar
- 1 1/4 cups all-purpose flour, divided
- 1 tablespoon baking powder
- 1 teaspoon kosher salt
- 3/4 cup smooth peanut butter


The recipe actually called for stiring the eggs instead of beating them, and since the egg yolk is used to keep the CO2 from escaping, and CO2 is used to help the brownies rise, My brownies ended up to be almost 2 in tall!! I think I overcooked them a little, but they were still delicious! This sure was a yummy project!

Photo credit: my dad! :)

Mills Creek Canyon Park!!!!

On Thursday all of Mr. Olson's class took a field trip to Mills Creek Canyon Park. As you can see in the map below, we walked all the way there. I can assure you, that the walk up Martinez Dr. was not easy. It was fun though, just being able to take a break from the classroom and enjoy the sun and everything else nature had to offer. There were about 150 some kids I think, so it was kinda of chaotic, but still awesome to hang out with friends. It was hot because we were walking up pretty steep hills and all, and the ground was muddy from the rain the previous day, but I think most of us did not mind it so much.

I didn't see many animals, well, actually, I saw a dead lizard in the street and a rolly polly but no birds or little critters. I did get to enjoy the green trees, and beautiful flowers that were in full bloom. They were gorgeous! The view was also pretty cool and we could see the houses and the airport at one point in the hike.

We walked around following the trail for an hour and then we ate lunch and socialized. Some people went back down to the creek and I know my friends found this secret trial of some sort and played in a hammock that was hanging on the tree. I had to leave early because of a swim meet, but overall it was't so bad. I was really tired after we got because of all the walking, but I think it was a good kind of tired.

Here's a map of the route we took from Mills to the Park. Make sure you click on the icons because I've put pictures of me and my friends on them.


View Mills Creek Canyon Park in a larger map

I Propose We Burn Money! =]

Did you say burn money?! YUP! Here's how you do it...

Materials:
-dollar bill
-tongs
-water
-alcohol
-a lighter
-salt, or to color the flame: use Potassium Chloride for a purple flame, or Copper Chloride for a green flame

Procedure:
1. Make a solution with 50mL of water and 50mL of alcohol.
2. Mix in a pinch of salt or chemical of choice to color the flame.
3. Soak the dollar bill in the solution of water, alcohol, and salt until it is completely wet.
4. Use the tongs to hold the bill and move it away from the solution.
5. Light the dollar bill on fire; watch and wait until the fire burns out.

Safety Precautions:
-wear goggles, just in case!
-have an easy access to water near by in case you burn yourself.
-use tongs to prevent burning yourself
-have an adult near by if you are a minor.
-ask for help if needed.

The Science Behind It:
COMBUSTION!
C₂H₅OH + 4 O₂ -> 2 CO₂ + 3 H₂O + energy
The alcohol is what burns, instead of the dollar bill itself. The flame is also not hot enough to burn the water, since water has a high heat capacity. Therefore, since the water is not burned away, the dollar bill itself does not burn either. In the end, the flame burns out itself, leaving a damp dollar bill.