AP Chemistry : Gases
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Example Questions
Example Question #13 : Ideal Gas Law
A mixture of three gases in a balloon is able to generate 2 atm of pressure. The identies and amounts of each gas are as follows. 2 moles of O2, 3 moles of N2, 5 moles of H2.
What is the partial pressure of Oxygen gas?
0.4 atm
0.5 atm
4 atm
2 atm
1.6 atm
0.4 atm
Partial pressure is the amount of pressure that is the result of one gas. This is calculated by mutiplying the mole fraction of the gas by the overall pressure. The mole fraction is calculated as the moles of the compound of interest divided by the total amount of moles present. 2 moles O2/ 2 moles O2 + 3 moles N2 + 5 moles H2 = 2/10 = mole fraction of O2. 2/10 multiplied by the total pressure gives us the answer as 0.4 atm.
Example Question #141 : Solutions And States Of Matter
A mixture of gases is present in a container. The total pressure on the container is 12atm. Six moles of one of the gases accounts for nine atmospheres of pressure. What is the molar fraction of the remaining gases in the container?
There are a couple of things to consider in this problem. First, the problem asks for the molar fraction of the remaining gases in the mixture. As a result, we do not need to know how many different gases are in the mixture, since they all have the same effect on the pressure in the container. Second, the number of moles that one gas accounts for is not relevant since the question is asking to find the molar fraction for the remaining gases. Knowing this, we can find the molar fraction for the described gas, and then subtract it from the total in order to find the remaining molar fraction. The equation for partial pressure is written as 
Since we know how much pressure one gas accounts for, we can solve for the molar fraction of that particular gas.
In other words, the known gas accounts for 75% of the gas molecules in the container. This means that the remaining gases must account for 25% of the gas molecules in the container.
So, the molar fraction for the remaining gases is 0.25.
Example Question #41 : Gases
If a container holds 1mol of hydrogen, 2.5mol of helium, and 2mol of oxygen at a total pressure of 4atm, what is the partial pressure of the oxygen gas?
According to Dalton's law of partial pressures, when two or more gases are in one container without chemical interaction, each behaves independently of the others. The partial pressure of oxygen can, therefore, be found by multiplying the molar fraction of oxygen in the container by the total pressure of the three gases.
Example Question #12 : Ideal Gas Law
A glass container holds a mixture of two gases. Gas A exerts a pressure of 5atm on the container.
If there are twice as many moles of gas A as there are moles of gas B in the container, what is the total pressure in the container?
The pressure is unaffected by the gas of lower concentration
This is an equation which requires us to find the partial pressures of each gas in the container. The equation for partial pressure is 
Example Question #42 : Gases
A gas mixture at equilibrium held over water at 
The molar quantity of a gas is directly proportional to its partial pressure, so if we have a total of 12 moles of gas, and 
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