Chemistry and Gases Help (page 3)

By — McGraw-Hill Professional
Updated on Aug 29, 2011

Standard Temperature And Pressure

When studying the gas laws, you will sometimes see a problem talk about standard temperature and pressure (STP). Table 17.2 lists the values for temperature and pressure that are called gas standards .

Table 17.2 Using standard temperature and pressure units for gases makes conversions simpler.

Gases Standard Temperature And Pressure

Vapor Pressure

Since some gases are non-polar and don’t mix with water, they can be collected using water as a filter. Water is displaced by the gas that is bubbled through it and collected. The vapor pressure of a gas is directly affected by temperature. As temperature increases, vapor pressure increases.

Vapor pressure of a sample is equal to the partial pressure of the gas molecules above the liquid phase of the sample added to the pressure of the water vapor.

P total = P gas collected + P water pressure

P gas collected = P totalP water pressure

Molar Volume

To figure out the volume of a mole of gas, use Avogadro’s number of 6.022 × 10 23 molecules in a mole. To figure out the molar volume of a gas, multiply the density times its molar mass.

Molar volume describes the density of a gas times its molar mass. At STP all gases have the same molar volume.

Molar volume = d × m

The density of oxygen at STP is 1.43 grams/liter and its molar mass is 32.0 grams/mol. To figure out the molar volume of oxygen at STP, use the following formula:

32.0 grams/mol × 1 liter/1.43 grams = 22.4 liters/mol

Since Avogadro’s number is so huge, every gas works out to be very close to 22.4 liters/mol, so it is commonly said that the molar volume of every gas at STP is 22.4 liters/mol.

The activity of gases can be calculated using a lot of different ratios. If you know the temperature, pressure, and volume of gases, then lots of different ideas can be tested. The gas club is definitely the most changeable of the solid, liquid, and gas forms of matter.

Practice problems for these concepts can be found at – Chemistry and Gases Practice Test

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