gas laws

Unit 5 Application Assignment: Gas Laws There are 4 gas variables that are used to describe the behavior of gases. These 4 variables are in a delicate balance and if one of the variables is changed, one or more of the variables may change relieve the stress on the gas system. This activity is designed to look at what happens when you change 3 of the 4 variables. We will keep the number of particles constant in each “experiment” and in addition, each experiment will hold an additional variable constant. Get Started 1. Click on this Gases Intro Phet Simulation to open the gas simulation 2. Choose the Laws option on the right. See picture Experiment 1- Constant volume 1. Give one pump of gas into the chamber. See picture 2. Choose to hold the volume constant by selecting that option in the upper right hand corner. See the picture. What is the initial temperature (in K) and pressure (in atm) in the chamber? 5.8atm 3. Use the slider at the bottom of the simulator to add heat and double the temperature. Did the pressure go up or go down? What is the new pressure in the chamber? The pressure went up, the new pressure is 11.5atm. Experiment 2 - Constant Temperature 1. Reset the simulator by selecting the reset button in the bottom right corner of the simulation. 2. Give one pump of gas into the chamber. 3. Choose to hold the temperature constant by selecting that option in the upper right hand corner. See the picture. What is the initial pressure (in atm) in the chamber? 5.8atm 4. Locate the handle on the left of the chamber and slide it to the right as far as it will go. Does the volume go up or go down when you slide it to the right? Did the pressure go up or go down? The pressure went up.

5. Slide the handle all the way to the left as far as it will go. Did the pressure go up or go down? The pressure went down.

Practice Problems Gas Law Formula Description Boyle’s Law P 1 V 1 = P 2 V 2 At constant T, as P increases, V decreases. Charles’ Law V 1 = V 2 T 1 T 2 At constant P, as V increases, T increases. Gay-Lussac’s Law P 1 = P 2 T 1 T 2 At constant V, as P increases, T increases. Combined Gas Law P 1 V 1 = P 2 V 2 T 1 T 2 This equation is the combination of the previous three equations. Ideal Gas Law PV = nRT There are 4 variables (P, V, n, T) and one constant (R). R= 0.0821 L atm/mol K Remember to change all temps to Kelvin: K = ℃ + 273 1. The gas left in a used aerosol can is at a pressure of 1 atm at 27°C. If this can is thrown into a fire, what is the internal pressure of the gas when its temperature reaches 927°C? Given Variables: T1=300K P1=101kPa T2=1200K P2=x Work: 101/300=x/1200 x=404 Unknown Variable: P2 Formula: P1/T1=P2/T2 Answer: 4ATM 2. A sample of carbon dioxide occupies a volume of 3.50 L at 125 kPa. What pressure would the gas exert if the volume were decreased to 2.00 L? Given Variables: V1=3.5L V2=2L P1=KPA P2=x Work: 125(3.5)=2x x=218.75kPa

Unknown Variable: P2 Formula: P1V1=P2V2 Answer: 218.75kPa 3. Oxygen gas is at a temperature of 40°C when it occupies a volume of 2.3 L. To what temperature in Celsius should it be raised to occupy a volume of 6.5 L? Given Variables: T1=313K V1=2.3L T2=x V2=6.5L Work: 2.3/313 = 6.5/x x=884 Unknown Variable: T2 Formula: V1/T1=V2/T2 Answer: 611 C 4. Fluorine exerts a pressure of 90.0 atm. When the pressure is changed to 1.5 atm, its volume is 250. L. What was the original volume? Given Variables: P1=120kPa P2=151.5kPa V1=x V2=250mL Work: 120x=151.5(250) x=315.625mL Unknown Variable: V1 Formula: P1V1=P2V2 Answer: 315.625mL 5. A sample of N2 occupies a volume of 250 L at 25°C. What volume will it occupy at 95°C? Given Variables: V1=250ML T1=298K V2=x T2=368K Work: 250/298 = x/368 x=308mL

Unknown Variable: V2 Formula: P1V1=P2V2 Answer: 47L