PRACTICE MULTIPLE CHOICE QUESTIONS FROM UNIT 10
1.) A cylinder is filled with 2.00 moles of nitrogen, 3.00 moles of argon, and 5.00 moles of helium. If
the gas mixture is at STP, what is the partial pressure of the argon?
(A) 152 torr (B) 228 torr (C) 380. torr (D) 760. torr
2.) Compared to the average kinetic energy of 1 mole of water at 0 oC, the average kinetic energy
of 1 mole of water at 298 K is
(A) the same, and the number of molecules is the same
(B) the same, but the number of molecules is greater
(C) greater, and the number of molecules is greater
(D) greater, but the number of molecules is the same
3.) If the pressure on a given mass of gas in a closed system is increased and the temperature
remains constant, the volume of the gas will
(A) decrease (B) increase (C) remain the same
4.) Which gas has approximately the same density as C2H6 at STP?
(A) NO (B) NH3 (C) H2S (D) SO2
5.) At a temperature of 273 K, a 400. milliliter gas sample has a pressure of 760. millimeters of
mercury. If the pressure is changed to 380. millimeters of mercury, at which temperature will
this gas sample have a volume of 551 milliliters?
(A) 100 K (B) 188 K (C) 273 K (D) 546 K
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Considering the Dalton's partial pressure and STP conditions, the total pressure of argon in the mixture of gases is 0.3 atm.
On one side, the STP conditions refer to the standard temperature and pressure. Pressure values at 1 atmosphere and temperature at 0 ° C are used and are reference values for gases. And in these conditions 1 mole of any gas occupies an approximate volume of 22.4 liters.
On the other side, the pressure exerted by a particular gas in a mixture is known as its partial pressure.
So, Dalton's law states that the total pressure of a gas mixture is equal to the sum of the pressures that each gas would exert if it were alone:
[tex]P_{T} =P_{1} +P_{2} + ... + P_{n}[/tex]
where n is the number of gases in the gaseous sample.
Dalton's partial pressure law can also be expressed in terms of the mole fraction of the gas in the mixture.
So in a mixture of two or more gases, the partial pressure of gas A can be expressed as:
[tex]P_{A} =x_{A} P_{T}[/tex]
In this case, the mole fraction of the argon can be calculated knowing that:
Then:
[tex]x_{argon} =\frac{3 moles}{10 moles} = 0.3[/tex]
So, if the gas mixture is at STP, the total pressure of the gas mixture is 1 atm and the partial pressure of argon can be calculated as:
[tex]P_{argon} =x_{argon} P_{T}[/tex]
[tex]P_{argon} =0.3x 1 atm[/tex]
[tex]P_{argon} =0.3 atm[/tex]
In summary, the total pressure of argon in the mixture of gases is 0.3 atm.
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