Next, Mr. H projected Emma's blog on the screen and went over the specific heat for each phase of thermochemistry and other main ideas. He also talked about how Emma's blog was very useful, because it explained how to do phase change calculations very well. If you are someone who is confused about phase change calculations and heating curves, i would recommend that you refer to Emma's blog.
After going over Emma's blog, Mr. H had the everyone open their packets to page 15. He reiterated the idea that if you lower the pressure around an element, then you can boil it; just like yesterday's demo. Mr. H then focused the rest of his time on page 15 to go over some of the answers and explain how to use the graph. He explained to the class, while using the graph, that at any given temperature, if you were to increase the pressure, then, an element would change its phase to either a solid or liquid (depending on the temperature of course). He also explained how if you were to decrease the pressure while at any temperature, then that element would turn to gas. For those of you who are still confused on how to use the graph on page 15, i would recommend trying to do problem #2 on page 15. For instance, if you want to find the phase type of an element when its pressure is 1atm and its temperature is 300°C, the answer would be a liquid. You would find this answer by using your finger and going along the x-axis and finding 300°C, then you would use your finger and go up the y-axis until you found 1atm. Then, you would slide your finger from the y-axis, to the right until you got to the point where 1atm and 300°C met. From there, you would look at which part of the graph you were in (solid,liquid,gas) and then record that answer. Its pretty simple once you understand how to do it.
After Mr. H explained how to use the graph, he then worked with the class on problems #3-5 and then he had the class do the rest on our own. the answers are as followed:
#3) Solid
#4)100°C
#5) 450°C
#6)175°C
#7) T=100°C P=0.70atm
#8) No, because although it is in the liquid state, its minimum temperature would have to be 100°C
#9) Melting
#10) 1st: Condensation 2nd: Freezing
After going over the answers in class, Mr. H then prepared a demo for the class. Prior to the demo occurring, he got dry ice (CO2 as a solid) from a container and then went around the class and had some students hold it. He warned that you can't hold the dry ice for too long because then it would burn your hand, so he advocated that students should hold it as if they were holding a hot potato. He then proceeded to crush it up, put the crushed up pieces in what seemed to be a pill capsule and then closed the lid of the capsule while using pliers. This demo was significant because it showed the transfer of heat from the water to the dry ice in the capsule (endothermic). Mr. H was also trying to demonstrate how an element could reach the triple point in a reaction. Mr. H then proceeded to put the capsule of dry ice in a beaker of water while holding the capsule with a pair of pliers. At first, bubbles began to escape from the capsule, after a couple seconds, there was a mini-explosion. That occurred because enough pressure built up inside the capsule and when it couldn't hold any more, it caused this mini explosion to occur.
After doing this lab, Mr. H had everyone turn their packets to page 17. Once everyone did, he began to talk about Spontaneity, what it means, and what it would look like with real world examples. It is important to note that Spontaneity= reactions that occur naturally (once activated). Also, there are 2 factors to be considered, and they are:
- Enthalpy Δ (ΔH)
- Entrapy Δ (ΔS)
Next, Mr. H had us answer questions #1-2. The answers are as followed:
a) NS
b) S
c) NS
d)NS
e)S
f) NS
g)S
h)NS
i)S
#2) Tosh, because not all exothermic reactions are spontaneous
Once we finished talking about page 17, Mr. H did a special demo for the class. Mr. H prepared the demo by using Jovan's water bottle, then putting a lot of crushed up dry ice inside it and then closing the water bottle with the cap. Enough pressure built up inside the water bottle, and the outcome was similar to this:
^^this is similar to what Jovan's water bottle looked like after the reaction.
Mr. H advocated to the entire class not to do this type of experiment at home since it can have negative results. To conclude, today was mostly a review of phase calculations and phase diagrams and an introduction to Spontaneity. Tonight's homework: Webassign and study page 13 for the pop quiz.
