Pressure – Temperature Relationship in Gases

Chem I

PURPOSE:      Using your data and graph, you will determine what kind of mathematical relationship exists between the pressure and absolute temperature of a confined gas.

PROCEDURE:            1.   Submerge 125 ml Erlenmeyer flask into a water bath.

2.      Heat water, stir water with temperature probe to distribute the

heat as evenly as possible.

3.      Start collecting data.  Click collect

4.      Once a temperature is constant, click keep

Collect 5 temperature points.  Try to obtain temperatures that are 10 degrees apart from each other.

Example:          approximately (not exactly) 50, 60, 70, 80, 90

DATA:

 Pressure (atm) Temperature (oC) Temperature (K) Constant, k (P/T or P * T)

ANALYSIS:

1. Build a graph of pressure versus temperature (K).

1. In order to perform this experiment, what two experimental factors were kept constant? (Help)

1. Based on the data and graph that you obtained for this experiment, express in words the relationship between gas pressure and temperature. (Help)

1. Explain the relationship using the concepts of molecular velocity and collisions of molecules. (Help)

1. Write an equation to express the relationship between pressure and temperature (K).  Use the symbols P, T, and k (Help)

1. One way to determine if a relationship is inverse or direct is to find a proportionality constant, k, from the data.  If this relationship is direct, k = P/T.  If it is inverse, k = P*T.  Based on your answer to Question 5, choose one of these formulas and calculate k for the five ordered pairs in your data table.  Show the answer in the fourth column of the Data and calculations table.  How “constant” were your values?

1. According to this experiment, what should happen to the pressure of a gas if the Kelvin temperature is doubled?  Check this assumption by finding the pressure at –73oC (200 K) and at 127oC (400 K) on your graph of pressure versus temperature.  How do these two pressure values compare?

EXTENSION:

1. The data that you have collected can also be used to determine the value for absolute zero on the Celsius temperature scale.  Instead of plotting pressure versus Kelvin temperature like we did previously, this time you will plot Celsius temperature on the y-axis and pressure on the x-axis.  Since absolute zero is the temperature at which the pressure theoretically becomes equal to zero, the temperature where the regression line (the extension of the temperature-pressure curve) intercepts the y-axis should be the Celsius temperature value for absolute zero.