Real vs. Ideal Gases: van der Waals Explained for General Chemistry
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In developing the ideal gas
In developing the ideal gas law (PV=nRT), any attractions or repulsions between gas particles are ignored. In 1873, Johannes van der Waals adjusted the ideal gas law to include the effects of attractive forces (symbolized by a) and repulsive forces (given the symbol b).
Under certain conditions, the attractive forces of a gas are more dominant than the repulsive forces. van der Waals found that the real pressure of a gas was less than that predicted by the ideal gas law when the attractive forces were dominant.
Under certain conditions, the repulsive forces of a gas are more dominant than the attractive forces. van der Waals found that the real pressure of a gas was greater than that predicted by the ideal gas law when the repulsive forces were dominant.
The van der Waals equation is one of may relationships that describes the deviations we expect in measuring the pressure of a gas in a container, compared to the theoretical ideal gas value.
Many people call the repulsive forces the "excluded volume" because the size of each gas particle takes up some space in the volume of the container...the V in the ideal gas law. Since repulsive forces won't allow two particles to occupy the same space, the excluded volume is really a way of talking about the repulsive forces between any two particles.
The attractive forces between molecules in a gas are intermolecular forces (IMF) and are weak.
Under certain conditions, the attractive forces of a gas are more dominant than the repulsive forces. van der Waals found that the real pressure of a gas was less than that predicted by the ideal gas law when the attractive forces were dominant.
Under certain conditions, the repulsive forces of a gas are more dominant than the attractive forces. van der Waals found that the real pressure of a gas was greater than that predicted by the ideal gas law when the repulsive forces were dominant.
The van der Waals equation is one of may relationships that describes the deviations we expect in measuring the pressure of a gas in a container, compared to the theoretical ideal gas value.
Many people call the repulsive forces the "excluded volume" because the size of each gas particle takes up some space in the volume of the container...the V in the ideal gas law. Since repulsive forces won't allow two particles to occupy the same space, the excluded volume is really a way of talking about the repulsive forces between any two particles.
The attractive forces between molecules in a gas are intermolecular forces (IMF) and are weak.
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