AP Chemistry - Gas Laws Practice Test Answer KeySolve the following problems. Show all work. Use correct units. Assume that all gases behave ideally unless the problem states otherwise.

1. Two gas particles are bragging about the distance running they used to do in high school. If the two gases, methane (CH4) and oxygen gas, run an ultra-marathon who will run the farthest and how much farther will they run? (An ultra-marathon is a 24 hour race, in which each runner goes as far as they can in the twenty four hours. Winners are determined by distance alone since the time is the same for each runner.)

By Graham’s Law:sqrt(Mass A/Mass B) = velocity B/ velocity A

Let A = methane, B = O2

sqrt(16.0425/31.9988) = velocity B/ velocity Avelocity B = 0.708059 velocity A

or, velocity A = 1.41141 velocity B

CH4 will go 1.412 times further than O2

2. If a tanker car is filled with 1.000 x 105 g of helium gas so that the pressure inside the 3000.0 L tanker is 20057 mm Hg, what is the temperature of the car?

3. The gas in #2 behaves ideally under the conditions described. Why?

Temperature is extremely low - normally, stickiness would increase. However, the He atoms are extremely small, keeping collisions virtually elastic. The atoms therefore hit the walls of the container as they would in an ideal situation, causing pressure to be ideal. Additionally, the container of the He is large enough that the molecules maintain their distance from one another (for the most part) and do not attract.

4. If a can of Lysol is designed to withstand internal pressures of up to 4.500 atm, how hot must the can get before it explodes, assuming that it has a volume of 0.400 L and an initial pressure of 3.00 atm at a temperature of 25.7ºC?

5. Hydrogen gas is collected over water as you did in the experiment with the magnesium and concentrated hydrochloric acid. The temperature of the gas collected is 23.7oC and the pressure in the room is 778.3 mm Hg. If the volume of the gas is 45.00 ml and the vapor pressure of the water is 21.3 mm Hg how many grams of magnesium were used in the reaction. (Assume complete reaction and no loss of gas.)

0.0447 grams Mg

Answer the following questions. Make sure that your answers are as complete as possible. (Most answers will require a discussion of molecules)6. Why does the pressure of a gas go up when the temperature does?Pressure is defined as force over area. When temperature increases, the gas molecules have more kinetic energy, meaning they hit the walls of the container harder and more often, thus increasing force, while area remains constant. Since force is in the numerator, an increase in force will cause the pressure to increase.

7. What is true about gases at the same temperature?

They have the same kinetic energy. Kinetic energy is . If a very massive molecule and a very light molecule have the same kinetic energy, the massive molecule will have a very low velocity while the light molecule will have a high velocity.

8. Derive Graham's Law from the kinetic energy expression. SHOW WORK.

9. Why is a decrease in volume accompanied by an increase in pressure?This happens because there is less room for molecules to bounce against the walls of the container that they’re in so these molecules have to bounce against the walls more often. If pressure is force/area, then area is getting smaller while force increases, so pressure has to increase.

10. What is pressure?Pressure is the measure of force over area. This means how much something pushes on a surface over how much area that force is spread over. If the same force is spread over a smaller area, the pressure will increase. For more details, see http :// abetterchemtext . com / gases / pressure . htm

11. How does a straw work?http :// abetterchemtext . com / gases / straw . htm

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