Hess's Law

Through our excitement filled class today, we not only got a glimpse at carbon dioxide and nitrogen's triple point, but we also learned about the amazing science that is Hess's Law. We started off with a demo, where we were instructed to put on our trusty viser-gogs and crouch around the front table. Assuming the lab was going to be a harmless one, as the dry ice started to melt, we slowly got closer. With Mr. Lieberman encouraging us to get a closer look, we were all surprised when it exploded, showering everyone with water. This caused more then a few screams, one of which from the notorious Korri and even the stoic people of the class were startled by this outburst.

From there we moved on to Hess's Law, as depicted in slides 33-59 in the following slides:

Hess Law And Thermodynamics

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After learning about this law and Mr.Lieberman's super power affiliated with it, we observed Nitrogen's triple point. This we used a vacuum to ensure an extremely low pressure and though it was not as thrilling as the last, the outcome was interesting to watch. The bubbles rose and dropped continuously as the pressure reached the triple point. From then to the end of the class we proceeded to practice more enthalpy problems which we all somewhat mastered by the end.

Make sure to do the homework and practice practice practice as it makes perfect.
And the moment you've all been diligently checking the blog for is here! The next scribe will be...Ellen H. congratulations

All About Phases

Today in chemistry class we started out by learning about phase diagrams. They are representations of the state of substances based on the temperature and pressure conditions. The pressure is listed on the y-axis( in mmHg) and the temperature on the x-axis (in degrees celsius). The points on the graph indicate that states are in equilibrium. Point A, the triple point, is a point where all three states are in equilibrium. If a substance is gotten to exactly the right temperature and pressure of its triple point, all three states will be present.

We learned that the state of a substance can be manipulated by using pressure. For example, a tank of propane gas used for grilling is kept at high pressure in order for it to remain in liquid state in the tank before it is needed. However, when the valve is open to get the propane gas to the grill, the pressure is lessened and the propane needed is changed to gas form.

Mr. Lieberman did a demo where he simulated boiling by putting dry ice in a beaker of water. He said that once the pressure in the gas bubbles equals the pressure in the water, vapor will be formed.

Mr. Lieberman also did a demo that proved that pressure affects the state of water and any other pure substance. He put a beaker of water inside a vacuum and started lowering the pressure. The water started boiling within 30 seconds and produced vapor.

Lastly, Mr. Lieberman showed us dry ice in all three states by putting some in a tube and sealing all the holes. He then held this tube into a beaker of water and we watched the dry ice turn into liquid form from its solid state. Also, we saw vapor bubbles frequently during many attempts at perfecting this demo. These vapor bubbles indicated the presence of a hole in the seal of the tube. Finally we saw dry ice in liquid form!

This has been Korri H!!

The next scribe is Katie I.

Don't forget to do the worksheet!

Hurts like Steam!

Today in chemistry class, Mr. Lieberman discussed with us how our tables should look like for the lab we did on January 24th, as shown by the image on the left.

The theoretical heat curve that can be observed has two platforms. The first platform is at the bottom left, which is the melting phase where the ice melts into a liquid. This platform only has temperatures from 0 degrees C to approximately 5 degrees C. After this melting phase, it is liquid, where it immediately gains energy and increases in temperature all the way to the boiling point. The boiling point is the second platform. Here, the water is boiled and vaporized into the air at the temperatures 100 degrees C to approximately 101 degrees C.

The amazing section of this lecture was that past beyond the vaporization

point, the temperature of the steam can keep increasing to an infinitely high number. This is equally true for the melting point, for before the ice melts, it can have an infinitely low temperature. Both of these situations is demonstrated by the picture below.

We also learned that during the melting phase \Delta H fusion = kJ/\o is the equation used to determine the heat in order to cause this physical change from solid to liquid. To f

ind the energy that is used to reach the boiling point, this equation must be utilized: q=M x C x \Delta T . And finally, to find the energy that is used to actually turn the water into vapor, this equation must be utilized: \delta H vaporization = KJ/ \o

Stepping aside from Chemistry for a moment, I give you a picture of a small monkey. Attempt to absorb his cute-ness and calculate the percent error of cute-ness absorbed versus the theoretical cute-ness that the monkey gives off.

Mr. Lieberman performed a demonstration where he had a coiled copper tube inside of a flask, which is has water and is on a hotplate. Once the water began to boil, the hot steam went into the copper tube. Under the coiled part of the copper tube, the steam trap, there was a burner that heated the steam substantially in order to prove that steam can be heated to a way higher temperature. This can be seen by the line graph farther above. The steam, however, was able to burn a hole through a sheet of paper and it was able to light a match!

The next scribe is Korri H.

Kickin'!

Watch the Ice MELT and then BOIL

Today in Mr. Liberman's class he started of by giving us five labs back that went on our semester 1 grade Next he handed out a calender of our continuation of Unit 7. Next he told us that there is a couple of Web Assign up for us to do. Also, he told us that the

question set for the second set of Unit 7 may not be done by paper, but by a Web Assign and he told us he'd give us his answer tomorrow. Then we switched seats and have new lab partners. Eventually we learned about our new lab format. Where we are given a sheet with less post-lab questions YES! and no pre-lab. It is a more organized format that helps us come to the conclusion of our labs better this lab was called Heating Curve Lab. The first part of the lab was to write the lab goal which in this case is to use a heating curve to determine the temperature at which a sample of ice melts and boils.

The procedure of this lab is as follows: First we obtained 150 mL beaker of crush iced which we took the initial temperature of, for my group it was -.02 degrees celsius. After we began heating it until it melted which was .1 degrees celsius because this is when the ice started to turn into water. Next we began checking the temperature of the water every minute until it began to boil which was 90.0 degrees celsius and after we raised the hot plate to the highest temperature for 3 more recoreded temperatures. Next we had to make a graph of our data so i made my like the photo above. You use your time as the x coordinate and temperature as the y. Next you had to do the percent error for your boiling temp vs. the actual which is 1oo degrees celsius. To do this you do 90.o + 273 (kelvin) -100.o + 273/ 373 which is -2.7 % error which is not but that is what my data states. This is correct because you do actual -theorectical/ theorectical. So my actual was 90 degrees because that is when ours began to boil. Then you do the same thing for melting so my group was .1 degrees celsius so you do .1 + 273 - 0 -273/ 373= .037 % error. You use 0 because that is the melting point of water. So to answer the first post lab question you give your own boiling and melting point of water. To answer the second you explain how you got it and, finally for the third you explain what you may have done wrong like in my case where I got -2.7 % error. Well that is about is the next scribe is Emillio I.