Dalton's Law of Partial Pressure

Consider a container with three different gasses (e.g ). The molecules of each gas collide with the container walls and with the sensor on the pressure gauge. Each gas exerts a pressure called its partial pressure.

A closed container contains a mixture of and . If the pressure is and the temperature is , calculate the partial pressure of if the mixture is .

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of and of are placed in a container at . What are their partial pressures and the total pressure in ATM?

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Convert mass to moles:

Use Ideal Gas Law to find pressure:

What is the final total pressure if the barrier between the two containers is removed?

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The chemical composition of air that is exhaled is different from ordinary air. Is the density of expired air greater or less than that of ordinary air at the same temperature and pressure?

Volumetric analysis:

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The formula for average molar mass:

So for each:

Gas density formula:

we have , so exhaled air has lower density.

A gaseous mixture of acetylene () and carbon monoxide () is contained in a rigid vessel at and . The mixture is burned in an excess of . The total pressure of the gaseous and produced by combustion was measured to be in the same vessel at .

What is the mole fraction of in the original mixture?

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Chemical equations:

Assume that at , is an ideal gas.

Comparing the moles of the gasses we are considering (i.e ignoring oxygen, since it's not a factor in the original pressure), we have:

Since we have constant , from , we know .

• At the beginning, we had
• At the end, we had

Now we solve the system. From the first part, we have , and then and .

To find the pressure of , we can relate it to the number of moles directly:

Finally, to find the mole fraction:

A container holds a mixture of ethene (), ethane (), and oxygen at a total pressure of and temperature of . The mixture is ignited and all reactants completely combust to form carbon dioxide and water, according to the unbalanced reactions below.

The mixture is then cooled to and the water is removed from the vessel, leaving only carbon dioxide at a total pressure of . What is the mole fraction of oxygen in the original mixture?

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Balancing the equations:

In terms of moles, we have:

Since we have constant , we have .

• At the beginning, we had
• At the end, we had

Solving, we have and .

Finally, to get the pressure of oxygen, we can relate it to the number of moles directly:

To find the mole fraction: