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Place the following gases in order of decreasing average molecular speed at 300K: He, SF6, SO2, Ar

User Terminador
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Temperature is a way to measure the kinetic energy of the molecules of gases. The kinetic energy is a kind of energy that a moving body has. it is related to the mass of the body and the speed they are moving. The kinetic energy can be calculated as:


E_k=(1)/(2)mv^2

Where Ek is the kinetic energy, m is mass of the molecules and v is the speed of the molecule

Knowing that gasses with the same temperature have same kinetic energy, then gasses with larger mass will move slower and viceversa.

Since the molar mass of those gases are:

He: 4.00 g/mol

SF6: 146.06 g/mol

SO2: 64.066 g/mol and

Ar: 39.948 g/mol

the ligther gasses move faster and the hevier slower, so we just have to order them by increasing mass:

He, Ar, SO2 and SF6

User Carl Sagan
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