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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

image\27236 Ch 6-no Alpha Chanel.png


If the Vander Waal constant a is found to be zero for gas A, what are true regarding this gas?

I. Gas A does not behave ideally.

II. Gas A behaves ideally.

III. Gas A is Xenon.



A I only
B II only
C II & III only
D III only
Ans. A A value of zero alone will not ensure ideal behavior. So gas A does not behave ideally. Hence item I is correct. Item II contradicts what we just said. We cannot say whether gas A is xenon. So item III is not a valid statement.

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