Suppose you start with a liquid mixture of 60% nitrogen and 40% oxygen.
Describe what happens as the temperature of this mixture increases. Be sure to
give the temperatures and compositions at which boiling begins and ends.
Liquid nitrogen will evaporate first as the temperature rises to -196 C, but the O2 will not start evaporating until the temperature reaches -183 C, the boiling point of pure O2.. While the liquid N2 is evaporating first, some O2 from the air will condense into the mixture, making it even richer in liquid O2. Finally, the liquid wil be almost all O2 as it all boils away at -183 C.
To describe what happens as the temperature of the liquid mixture increases, we need to consider the boiling points and compositions of nitrogen and oxygen.
First, let's understand the concept of boiling point. Boiling is the phase transition from a liquid to a gas that occurs when the vapor pressure of the liquid equals or exceeds the atmospheric pressure surrounding it.
The boiling points of nitrogen and oxygen are different due to their distinct molecular properties. Nitrogen boils at a lower temperature compared to oxygen. At standard atmospheric pressure, nitrogen boils at approximately -196 degrees Celsius (-321 degrees Fahrenheit), while oxygen boils at approximately -183 degrees Celsius (-297 degrees Fahrenheit).
Now, let's analyze the temperature range for the given liquid mixture of 60% nitrogen and 40% oxygen.
Since the mixture is currently in a liquid state, it means the temperature is below the boiling point of both nitrogen and oxygen. As we increase the temperature, the liquid mixture starts to heat up.
At a certain temperature, the composition of the vapor formed above the liquid mixture will begin to change. This happens because the molecules with lower boiling points (in this case, nitrogen) tend to evaporate first.
As the temperature rises, more nitrogen molecules will evaporate, increasing the nitrogen content in the vapor phase. Consequently, in the liquid phase, the remaining liquid will have a higher oxygen concentration.
At the boiling point of nitrogen (-196 degrees Celsius), the nitrogen in the liquid mixture will start to boil and transform into a gas. However, since oxygen has a higher boiling point, it will still remain in the liquid phase.
Therefore, at the boiling point of nitrogen (-196 degrees Celsius), the composition of the vapor phase will be richer in nitrogen compared to the initial mixture.
Continuing to raise the temperature, the liquid mixture will approach the boiling point of oxygen (-183 degrees Celsius). At this temperature, oxygen will also start to boil, and the vapor composition will become more oxygen-rich.
Finally, at a temperature higher than the boiling point of oxygen (-183 degrees Celsius), the entire liquid mixture will have transformed into a gas, and the composition of the vapor phase will be the same as the starting composition (60% nitrogen, 40% oxygen), as both gases will be fully evaporated.
In summary, as the temperature increases, the boiling of nitrogen begins at -196 degrees Celsius, leading to an increase in nitrogen concentration in the vapor phase. The boiling of oxygen begins at -183 degrees Celsius, resulting in a transition from the liquid to the gas phase for both gases. At temperatures above -183 degrees Celsius, the entire liquid mixture will be in the gas phase, maintaining the initial composition (60% nitrogen, 40% oxygen).