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General Chemistry

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Gases

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The behavior of gases can be predicted to a large extent on the basis of various laws. Gases are expressed mainly in terms of pressure, volume, and temperature. Many gases obey the ideal gas laws and those gases are called ideal gases. If we are not doing precision experiments, we can normally ignore the slight deviations that occur under normal conditions. Nevertheless, we cannot completely ignore the deviation factors.

According to Boyle's law, the pressure is inversely proportional to the volume at a constant temperature. Charles' law states that the volume is directly proportional to the temperature at a constant pressure. Combining these laws and Avogadro's law gives the combined gas law.

PV = nRT

(The ideal gas law)

Not all gases behave ideally. There are often deviations from the ideal behavior. At low temperatures, gases often behave differently apart from what is described by kinetic-molecular theory of gases. Considering these correction factors, the modified gas equation is:

The correction constants or Vander Waal constants, a and b, of gases are experimentally found. The Van der Waal constants of some gases are given in Table 1.


Table 1

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What is the most likely Van der Waal constant correction factor of bromine?

A 0.97 L2.atm/mol2
B 2.34 L2.atm/mol2
C 5.32 L2.atm/mol2
D 9.80 L2.atm/mol2
Ans. D The clues to answer this question have to be taken from the given data. What can we infer from the data given about halogens? The correction factor of fluorine is 1.170 L2.atm/mol2. The correction factor of chlorine is 6.340 L2.atm/mol2. By analyzing the trend, we can deduce that bromine must have a correction factor that is higher than that of chlorine. The only value that is higher than that of chlorine is 9.80 L2.atm/mol2. Hence, the best choice is D. If you were looking at the values of b, you probably did not notice the units represented in the answers. All units correspond to that of constant a and not of b.

Gases Flashcard List

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The behavior of gases can be predicted to a large extent on the basis of various laws. Gases are expressed mainly in terms of pressure, volume, and temperature. Many gases obey the ideal gas laws and those gases are called ideal gases. If we are not doing precision experiments, we can normally ignore the slight deviations that occur under normal conditions. Nevertheless, we cannot completely ignore the deviation factors. According to Boyle's law, the pressure is inversely proportional to the volume at a constant temperature. Charles' law states that the volume is directly proportional to the temperature at a constant pressure. Combining these laws and Avogadro's law gives the combined gas law. PV = nRT (The ideal gas law) Not all gases behave ideally. There are often deviations from the ideal behavior. At low temperatures, gases often behave differently apart from what is described by kinetic-molecular theory of gases. Considering these correction factors, the modified gas equation is: The correction constants or Vander Waal constants, a and b, of gases are experimentally found. The Van der Waal constants of some gases are given in Table 1. Table 1 Based on kinetic-molecular theory, which of the following are true? I. At a given temperature, all gases have the same average kinetic energy. II. At a given temperature, different gases have different average velocities. III. The average kinetic energy is proportional to the absolute temperature.A I onlyB II onlyC I & III onlyD I, II & III