14. Chemical Equilibrium
The General Equilibrium-Constant Expression
 Exercise. From the abundance table in Chapter 7, what are the concentrations of H and He atoms in the entire universe, expressed in mole fractions? Answer. = 0.928 = 0.072 The other common concentration unit for gases is partial pressure, . In a mixture of gases, each gas molecule moves independently, and every gas in the mixture behaves as if it were alone in the same volume. In a mixture of gases, if one molecule out of every three is a moIecule, then the chlorine gas acts as if it alone occupied the same volume with the same total number of molecules, or one third the total pressure. If the total pressure is 1 atm, then the partial pressure of gas is one third of an atmosphere. In any gas mixture the partial pressure of each component is its mole fraction times the total pressure from all gases: = x Thus oxygen gas in our atmosphere has a partial pressure of 0.20 atm and nitrogen gas has a partial pressure of 0.80 atm. The sum of partial pressures of all components in a mixture must add to give the total pressure of the mixture.
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