Due Today: Pressure Worksheet

Due Monday: Ideal Gas Law Worksheet

Today, we learned many new things about gases like ideal gas law and saw the properties of gases in action by seeing many cool demos. 

First, we talked about the many laws that gases and pressure follow.

The first law is Boyle's Law: 

Boyle's law states that pressure is inversely proportional to volume. In other words, as Pressure goes up, volume goes down, and as pressure goes down, volume goes up. 

This can be written as:  P1V1=P2V2

 Mr. Lieberman Showed us a real life example of this by putting a balloon in a pressure chamber. When Mr. Lieberman decreased the pressure in the chamber, the volume of the balloon went up and the balloon got bigger.

                                                       

 When Mr. Lieberman increased the pressure in the chamber, the balloon shrunk and the balloon went back to normal size because the pressure went up so the volume went down.

The next law that Mr. Lieberman talked about was Charles's Law, which states that: The volume of a gas is directly proportional to the temperature, and extrapolates to zero at zero Kelvin. In other words, this law says that as temperature goes up, volume goes up and as temperature goes down, the volume goes down. 

To show us this law, Mr. Lieberman poured extremely cold liquid Nitrogen into a container and put 2 very big balloons into the container. The baloons volume decreased dramatically because of the extremely low temperature. 

 

Here is the Equation: V1 =  V2

                                  T1      T2
For the law to mathematically work, the temperature must be in Kelvins!
Converting from Celsius to Kelvins is easy: Just add 273.15 to degrees Celsius.
20 degrees Celsius would become 293.15 Kelvins.

The next law Mr. Lieberman showed us was Gay Lussac's Law.
This law states: The pressure and temperature of a gas are directly related. In other words, as temperature goes up, pressure goes up, and as temperature goes down, pressure goes down.

To show us this law, Mr Lieberman put a pressure measurement instrument in the liquid nitrogen container. The Pressure started at around 15 psi, the normal pressure measurement on ground level.

But then after being in the extremely cold liquid nitrogen, the pressure decreased dramatically.

 The equation for this law is:  P1 =  P2

                               T1     T2

Like Charles's Law, the temperature in Gay Lussac's Law needs to be in Kelvins for the law to work mathematically. 

The next law is Avagadro's Law. This law states that: For a gas a constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures). In other words, gases with the sam amount of volume will have the same number of moles.

The Formula can be written as:  V1 =  V2

                                  n1      n2

N= the number of moles and V= the volume

The last law that Mr. Lieberman taught us was the Ideal Gas Law. This is just a combination of all the laws listed above so they don't have to be individually used. 

The equation for this law is:  PV=nRT

P= pressure in either atm, or kPa

V= volume in liters

n= the amount of moles present

R= The universal gas constant. 

In other words, if atm is used for pressure, then R would be .0821 atm/ mol K(change)

If kPa is used for the pressure, then R would be 8.314 kPa/ mol K(change)

T= the temperature, in terms of Kelvin. 

In the homework that is due Monday, the Ideal Gas Law worksheet, we use the Ideal Gas Law to solve the problems. Since Mr. Lieberman already explained how to do number 1 in class, here is how to do number 2.

2. What temperature must be maintained to insure that a 1.00 L flask containing .04 moles of oxygen will show a continuous pressure of 745 mm Hg?

The first thing that should be done is to convert 745 mm Hg to atm or kPa, because the pressure has to be in one of these two units. 

Here's how to convert it: 745mm Hg    1atm             = .98 atm

                                         760mm Hg 

 You should use the conversion factor of 1 atm per 760mm Hg so you can cancel mm Hg out and get the pressure in terms of atmospheric pressure, atm.

So, P= .98atm

The volume is 1.00 Liters because in the problem it says that the flask is 1.00 Liters.
So, V= 1L

The amount of moles is .04 moles because the problems says that that is how many moles of oxygen are in the flask.
So n= .04 moles

R is .0821 because that is the gas constant of atmospheric pressure, which is what the pressure unit is in this problem.
R= .0821

Finally T is not known because it is not given to us in the problem.
So T will remain T for now because it is the variable.

So knowing all of this: (.98atm)(1.00L)= (.04moles)(.0821)(T)
After multiplying it out, you should get .98= .003218T.
Divide both sides by .003218 and you should get 305.3.
Remember, temperature has to be in terms of Kelvin for this formula, so the answer is:
305.3 Kelvin

The Next Scribe is... Renee H.