Monday, May 2, 2011

Gas Laws

Recently in Chemistry, we have been dealing with the types of gas laws and then we even went into how all of those laws work together to create an ideal gas law. This ideal gas law helps you to identify unknown gases or pieces of the equations when one variable is needed.

Let's start back with the lab we did earlier this week. This lab was known as Boyle's Law: Pressure-Volume Relationship in Gases. This lab was based around the law K= P1 X V1 meaning that K (constant) is equal when the pressure and volume are multiplied together. This can also be written as P1 X V1 = P2 X V2 meaning that data has been collected about pressure and volume at one time should have about the same constant as data collected about pressure and volume recorded at a different time, therefore we set them equal to each other. When we preformed this lab, it was very simple, we used a
Volume and Pressure Connection
syringe and a gas pressure sensor connected to the computer to collect data that shows the connection between volume and pressure. We were trying to decide if pressure and volume were direct or inverse. The direct formula was P/V and the inverse formula was P X V and since that was our equation we knew these two conditions were inverse. The inverse conditions means that when volume decreases, pressure increases and when volume increases the pressure decreases.
If we analyse this data table from the first experiment we can tell that pressure and volume have an inverse direction. This graph clearly that as volume increases the pressure drops at a fairly rapid rate. From the 5.0ml to the 7.5ml the pressure drops about 44atm. From 7.5 to 10.0 and 10.0 to 12.5 the pressure drops about half of that amount. As the volume starts getting even larger we notice a less drastic pressure change, but it is still decreasing. This inverse relationship plays in with the ideal gas later explained later in my blog.
We did a few more labs after Boyle's Law, one of those including Pressure Temperature Relationship In Gases (Gay-Lassac's Law). In this lab our groups had a flask with just regular air in it. We had the flask sealed so that our pressure was always in a constant volume. Then, we took our flask around to different stations and placed our flask and temperature prob into bodies of water with different temperatures. We measured the temperature of 4 different tubs of water and our pressure for each we recorded as well. Our data read as follows:

From this data chart we can clearly see that as temperature increases pressure increases. Because both of these factors rise together we can infer that they have a direct connection between them when volume is constant. Finally, since these two are direct, their equation is know as K=P1/T1, which means that any point on the graph can be pressure divided by temperature and it should have the same konstant as another point on the chart. Because this is the case, just like Boyle's Law it means that P1/T1 = P2/T2. Again, this means that one pressure and temperature should be constant to another pressure and temperature calculation at another time and their constant will still be the same.

Finally, the third law is the law created by Charles. This law states that volume and temperature have a direct connection between them as well. So, if temperature increases, volume increases; if temperature decreases, volume decreases.  The equation is V1/T1 = K or V1/T1 = V2/T2. We did not do an experiment for this law, but we talked about it and because the connection is direct like the pressure and temp law, if data were collected the graph would look similar to the chart for that experiment of Gay-Lassc's law. Although we didn't do an experiment an easy example is of a helium balloon in a car. If the temperature is hot, the balloon has a good chance of popping because it's volume increases bigger than the balloon's barriers can hold. If it is a cold day, the balloon may shrivel up and sag.

As you can see from all of these experiments, these 3 factors play a large roll all together. Therefore, these factors, when placfed together make up the Ideal Gas Law. This law is written PV = mRT (pressure X volume = mass X constant R X temperature). This law can be used to find missing variables of an equation or identify the gas of an unknown substance. In order to do this we need to move the equation around to read M = mRT/PV. M stands for molar mass (g/mole). To find M, we must measure and plug in all of the other varibles. The varible m, is the mass (grams) of the substance. That is a good one to start with. Next, replace R with the number .0821 which is a constant. Then, measure your temp [degrees K (degrees C + 273)] and place it in the equation. Pressure is pretty constant at room temperature, but it can vary depending on altitude and humidity; here is La Junta, CO pressure at room temp is about .8 atm. Finally, calculate your volume and make sure it is in L not mL. When all of this is complete and the equation is calculated you will get what the gas's molar mass equals. This is a fun and easy way to identify and understand gases and their laws.

-working on data analysis and self analysis

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