Unit 9: Gases
Why a gas has no shape of its own, and how far you can push that idea before real molecules stop cooperating with the ideal gas law.
11 topics · 41 questions
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9.1 Gas Pressure and Its Units
- How it worksHow do trillions of gas particles slamming into a container's walls add up to what we measure as pressure?
- Worked exampleFind the pressure in atmospheres of a gas measured at 740 mmHg.
- Common mistakeWhy isn't gas pressure the same thing as the force of one single particle hitting the wall?
Your turn1 of 2
Find the pressure in atmospheres of a gas measured at 1105 mmHg.9.2 Boyle's Law: Pressure and Volume
- Common mistakeWhy doesn't Boyle's law apply if a gas's temperature is also changing at the same time as its volume?
- How it worksHow does squeezing a gas into a smaller volume, at constant temperature, force its pressure to rise?
- Worked exampleFind the new pressure of a gas that starts at 1.00 atm in a 2.00 L container and is compressed to 0.500 L at constant temperature.
- Going furtherWhat happens to the pressure-volume graph of a gas obeying Boyle's law once the experiment's temperature is raised?
Your turn1 of 2
A gas starts at 2.24 atm in a 4 L container and is compressed to 1.41 L at constant temperature. Find the new pressure.9.2 Charles's Law: Volume and Temperature
- How it worksHow does heating a gas at constant pressure make its particles push the container's boundary outward?
- Worked exampleFind the volume of a gas at 350 K if it occupies 2.00 L at 275 K, holding pressure constant.
- Common mistakeWhy does Charles's law require temperature to be measured in Kelvin instead of Celsius?
Your turn1 of 2
A gas occupies 4 L at 265 K. Find its volume at 394 K, holding pressure constant.9.2 The Combined Gas Law and Gay-Lussac's Law
- How it worksHow does the combined gas law let pressure, volume, and temperature all change at once while the amount of gas stays fixed?
- Worked exampleFind the final pressure of a gas that starts at 1.50 atm, 2.00 L, and 300 K and is changed to 1.00 L and 350 K.
- Common mistakeWhy isn't Gay-Lussac's law about volume changing at all, unlike Boyle's and Charles's laws?
- Going furtherWhat happens to a gas's pressure, under Gay-Lussac's law, if its rigid container can't expand and its temperature climbs sharply?
Your turn1 of 2
A gas starts at 2.24 atm, 3 L, and 315 K. Find the final pressure if it is changed to 0.71 L and 336 K.9.2 Avogadro's Law and Molar Volume
- How it worksHow does Avogadro's law connect the number of gas particles directly to volume, independent of what the gas actually is?
- Worked exampleFind the volume occupied by 2.50 mol of an ideal gas at standard temperature and pressure.
- Common mistakeWhy doesn't a gas's molar mass affect the volume one mole of it occupies at STP?
Your turn1 of 2
Find the volume occupied by 6.99 mol of an ideal gas at standard temperature and pressure (22.4 L/mol).9.2 The Ideal Gas Law
- How it worksHow do Boyle's, Charles's, and Avogadro's laws all combine into the single equation PV equals nRT?
- Worked exampleFind the number of moles of gas in a 5.00 L container at 2.50 atm and 298 K.
- Worked exampleFind the pressure exerted by 0.500 mol of gas in a 10.0 L tank at 350 K.
- Common mistakeWhy isn't R just a number you memorize without paying attention to the units attached to it?
- Ties togetherHow does the ideal gas law reduce back down to Boyle's law once temperature and moles are both held constant?
Your turn1 of 2
Find the number of moles of gas in a 7 L container at 3.42 atm and 390 K (R = 0.0821 L times atm per mol per K).9.3 Gas Density and Molar Mass from the Ideal Gas Law
- How it worksHow does rearranging the ideal gas law let you calculate a gas's molar mass from nothing but its density, temperature, and pressure?
- Worked exampleFind the molar mass of a gas that has a density of 1.964 g/L at 273 K and 1.00 atm.
- Common mistakeWhy isn't a gas's density a fixed property the way a solid's or a liquid's density is?
Your turn1 of 2
Find the molar mass of a gas that has a density of 2.24 g/L at 295 K and 1.453 atm (R = 0.0821 L times atm per mol per K).9.4 Dalton's Law of Partial Pressures
- How it worksHow does each gas in a mixture contribute its own partial pressure as though the other gases weren't even there?
- Worked exampleFind the total pressure of a mixture containing oxygen at 0.20 atm and nitrogen at 0.60 atm.
- Worked exampleFind the partial pressure of oxygen gas collected over water at a total pressure of 760 mmHg, given water's vapor pressure of 24 mmHg.
- Common mistakeWhy isn't a gas's partial pressure affected by other gas molecules physically bumping into it?
- Going furtherWhat happens to each gas's partial pressure once the mixture's total volume is compressed to half its original size?
Your turn1 of 2
Find the total pressure of a mixture containing oxygen at 0.587 atm and nitrogen at 0.554 atm.9.5 Kinetic Molecular Theory and Molecular Speed Distributions
- How it worksHow do the assumptions of kinetic molecular theory explain pressure and temperature purely in terms of particle motion?
- How it worksWalk me through how the Maxwell-Boltzmann speed distribution curve shifts and spreads out as a gas is heated.
- Common mistakeWhy don't all the particles in a gas sample move at exactly the same speed, even at one fixed temperature?
- Going furtherWhat happens to the average kinetic energy of a gas's particles when its Kelvin temperature is doubled?
Your turn1 of 2
An ideal gas's average kinetic energy per mole is (3/2)RT. Find the average kinetic energy per mole at 727 K (R = 8.314 J per mol per K).9.5 Graham's Law of Effusion
- How it worksHow does a lighter gas molecule's higher average speed let it escape through a tiny hole faster than a heavier molecule?
- Worked exampleFind the ratio of effusion rates between hydrogen gas and oxygen gas using Graham's law.
- Common mistakeWhy isn't effusion the exact same process as diffusion, even though both depend on molar mass the same way?
Your turn1 of 2
Find the ratio of effusion rates between a gas with molar mass 13 g/mol and a gas with molar mass 137 g/mol (rate1 divided by rate2 equals the square root of m2 divided by m1).9.6 Real Gases and the Van der Waals Equation
- How it worksHow do the van der Waals constants a and b correct the ideal gas law for real molecular attraction and real molecular size?
- Worked exampleFind the pressure predicted by the van der Waals equation for 1.00 mol of CO2 in a 1.00 L container at 300 K, and compare it with the ideal gas law's prediction.
- Common mistakeWhy doesn't a real gas behave ideally at very high pressure or very low temperature?
- Ties togetherHow do the deviations the van der Waals equation corrects for connect back to the intermolecular forces that also govern liquids?
Your turn1 of 2
Using the van der Waals equation for 1.00 mol of CO2 (a = 3.59 L2 atm/mol2, b = 0.0427 L/mol, R = 0.0821 L times atm per mol per K), find the predicted pressure in a 1.54 L container at 358 K.