Review on Gases: Chapter 14 March 2007
Part I: Multiple Choice with explanation: Circle the correct answer and justify your choice with an explanation, name of the gas law or with work to support your calculation.
1.
Reducing the volume of a contained gas from 3.0 L to 1.0L, while holding
temperature constant, means that the pressure: (a) decreased three times.
(b) increased three times. (c) decreased two times. (d) increased two times.
2. The pressure of a gas in a container is 76 cmHg. This is equivalent to: (a) 0.10 atm. (b) 1.0 atm. (c) 0.20 atm. (d) 0.76 atm.
3. If the temperature of a gas in a closed container increases: (a) the pressure of the gas decreases. (b) the average kinetic energy of the gas molecules in the container decreases. (c) the gas molecules collide with the walls of the container less frequently. (d) the pressure of the gas increases.
4.
Which of the following would double the volume of a gas in a balloon?
(a) doubling the pressure on the balloon (b) halving the number of particles in
the balloon
(c) doubling the Kelvin temperature of the gas in the balloon (d) none of these
5.
The average kinetic energy of particles is greatest in: (a) N2
at 200oC.
(b) Helium gas at 90oC. (c) CO2 at 373K. (d) O2
at 0oC.
Part II: Problems and Short Answers: Solve the
following problems or answer the questions in the space provided. Show steps.
[R = 0.0821 L-atm/(mol-K); 8.314 L-kPa/(mol-K)]
6. What volume would 25.0 g of CH4 occupy at 202.6 mmHg and 127oC? ***Name the law that you use.
7. A gas occupies a volume of 2.50 L at a temperature of 35.0oC. If the pressure remains constant, what volume would the gas occupy at standard temperature? ***Name the law that you use.
8. Helium is still ideal at -173oC and 0.675 atm. If the gas occupies a volume of 65.5 mL at these conditions, what will its volume be at STP, if the amount of gas does not change? ***Name the law that you use.
9. Charles’s Law describes the relationship between the volume that a gas occupies and the absolute temperature of the gas. Explain what happens to a fixed amount of gas at a constant external pressure in a flexible container is heated. In your explanation be sure to describe what is happening at the particle level, using the Kinetic Molecular Theory.
10. If two different gases fill a latex balloon, which one will effuse more quickly? If one gas is xenon and the other is carbon dioxide, how many times faster will the one effuse over the other?
11. A student lab team is competing for first place in a “Fill the Bottle” lab competition. The students are reacting magnesium carbonate with HCl in order to produce CO2 gas to fill a graduated cylinder with exactly 1.00 L of the gas. On the day of the competition the temperature is a sweltering 31oC and the pressure is 75.10 cm Hg. How many grams of MgCO3 do they need and how many moles of HCl do they need to provide to be sure that they will fill the bottle?
Balanced chemical equation:
If the student collects the CO2 over water at 99.7 kPa pressure and at a temperature of 31oC how should he account for collecting the gas over water? What volume would the dry gas occupy at STP if the vapor pressure of water was 3.2 kPa at 31oC? If the student realizes that CO2 is slightly soluble in water, what effect would this have on the amount of CO2 that he collected?
