Pressure Versus Temperature

Pressure Versus Temperature Relationship Lance Schell, Ben Latteman, Nathan Duda, and Eric Young Park Hill South High School Block Two Chemistry November 13, 2008

Abstract In this experiment, the purposeaim was to prove the ideal gas law, as well as find a value for absolute zero on the Celsius temperature scale e using the information discovered in the first part of the experiment. The absolute zero Celsius temperature value can be found by converting degrees Kelvin into degrees Celsius by subtracting 273.15°. [Results]

Introduction The theory behind the ideal gas law is that pressure bears an inverse relationship to temperature, and as such, when the pressure increases, the temperature of the gas will decrease. That is, of course, assuming a constant volume.

Absolute zero is the lowest possible temperature. Temperature is defined as a measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designed on a standard scale.2 Absolute zero therefore is a specific temperature at which all molecular activity ceases, or stops.3 The temperature itself is an impossible mark, as it is impossible (for the time being) to reach the approximate temperature of -273.15 °C. From this, one can infer that there is no such thing as “cold” in the world, but rather something colder than another is actually less hot, or contains less heat, which in turn, means less kinetic energy. The absolute part of the name comes from the fact that Kelvin and Rankine are both absolute scales of Celsius and Fahrenheit, respectively. Thus, the only point where Rankine and Kelvin are exactly the same is at zero, as zero is considered an absolute temperature.

Experimental The experiment was taken from the LabQuest 7: Pressure – Temperature Relationship in Gases experiment handout from Vernier Software. Data / Calculations In this experiment, we used two different equations to find the data we wanted. In an ideal gas versus a real gas, an ideal one When an ideal gas exists, we can use the pv=nRT equation developed by We used the first one to express the relationship between pressure and temperature, as well as using it for finding the number of moles of a gas, the volume of the gas, the pressure of the gas, or the temperature of the gas, depending on what information was given. P in this case stands for pressure [expressed in kilopascals (kPa)], v for volume [expressed in

liters (L)], n for the number of moles present, R for the constant (which is 8.31), and T which stands for temperature [expressed in degrees Kelvin (° K)]. The second equation allows us to convert the Celsius temperatures the LabQuest™ unit gives us into degrees Kelvin.

First Equation: Using PVNRT To Find Varying Values (Depending On Given Information) pv=nRT Example:

A biochemist at the University Of North Carolina School Of Medicine

wants to calculate

the amount of space an 18.00g sample of calcium

chloride will occupy with a

temperature of 100 degrees

Kelvin and a pressure of 1520 torr. Solution:

First, we convert the units given into the units we can use in the

equation. In this case,

the pressure of 1520 torr needs to be

converted into kilopascals (kPa). 1520 torrx kPa= 760 torr1 kPa We solve by cross multiplying and dividing by 760 torr to reach our answer of 2 kPa. 1520 torr1 kPa= 760 torrx kPa 1520 kPa760 = x kPa 2 kPa = x Next, we find the present number of moles of calcium chloride gas by adding the atomic

masses of calcium and chlorine.

40.08g Ca + 35.45g Cl=75.53g Calcium Chloride

The information found above tells us that 1 mole of calcium chloride (CaCl2) is equal to

75.53g. We now set up a proportion to find the

number of moles present. 18.00gx mol=75.53g1 mol 18.00g1 mol= 75.53g 18.00g75.53g=x mol .2383 = x mol

= Now, we continue with the problem by plugging the converted value, and all of the

other given information into the problem.

(2.00 kPa)(x L)= (.238n mol)(8.31)(100 °K) 2x=800

We finish multiplying the right side of the equation and divide by

two to reach our final

answer of 100 liters (L).

2.00x=200 x=100 L

Second Equation: Converting From Kelvin To Celsius, Finding Absolute Zero In Celsius °K-273.15=°C Example:

Suppose that a group of chemistry students had obtained data from

lab equipment and

were given all temperature data in degrees Celsius.

Calculators were able to convert all one -- 0°K. Using the formula given to you, find the

of the temperatures except for value for

zero on the Celsius scale (also known as absolute zero). {This is the exact problem used in our lab.} Solution:

We plug the temperature we are given into the equation.

0°K-273.15°=° C -273.15=° C We end up with a final answer in that 0° K is equal to -273.15° C. We now divide 70.09 by 9.88 to get the value for t, which is our temperature.

First, we plug all of our known information into the problem. t= 70.09 kPa9.88 L. 7.09 degrees Kelvin (° K)We now arrive at our answer (with significant figures) of t=7.09 ° K

°K-273.15= °CFor example, if we wanted to find the absolute value of zero degrees Kelvin in terms of degrees Celsius, we would plug our information into the equation as follows. (This is the actual equation we used to determine our answer in the experiment.)

0 °K-273.15= °C 0 °K= -273.15 °C

Conclusion [4 Pages To This Point] In this experiment, we aimed to prove the inverse relationship of pressure to temperature. we were able to determine that pressure and temperature have an inverse relationship to each other (see figures 1 and 2), and as such, when either one goes up or increases, the other must go down, or decrease.

Graphs and Figures

Figure 1: Pressure To Temperature Relationship (K)

References Microsoft, Absolute Zero, 2008, http://encarta.msn.com/encyclopedia_761552437/Absolute_Zero.html Georgia State University Department of Chemistry, Ideal Gas Law, 2008, http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegas.html