The apparatus shown consists of three temperature-jacketed 1.000-L bulbs connected by stopcocks. Bulb A contains a mixture of H₂O(g), CO₂(g), and N₂(g) at 25 °C and a total pressure of 564 mm Hg. Bulb B is empty and is held at a temperature of -70 °C. Bulb C is also empty and is held at a temperature of -190 °C. The stopcocks are closed, and the volume of the lines connecting the bulbs is zero. CO₂ sublimes at -78 °C, and N₂ boils at -196 °C.
(a) The stopcock between A and B is opened, and the system is allowed to come to equilibrium. The pressure in A and B is now 219 mm Hg. What do bulbs A and B contain?

Verified step by step guidance

1. Identify the physical states of the gases at the given temperatures. Since CO₂ sublimes at -78 °C and the temperature in Bulb B is -70 °C, CO₂ will remain as a solid in Bulb A and will not transfer to Bulb B. N₂ boils at -196 °C, so it remains as a gas at -70 °C and can transfer to Bulb B.
2. Consider the behavior of H₂O(g). Water vapor can condense at temperatures below 100 °C, and since Bulb B is at -70 °C, H₂O will likely condense when it enters Bulb B.
3. Calculate the partial pressures of the gases that can transfer to Bulb B. Since the total initial pressure in Bulb A is 564 mm Hg and the pressure after equilibrium is 219 mm Hg, the gases that transferred must account for the difference in pressure.
4. Determine the composition of gases in Bulb A after equilibrium. Since CO₂ does not sublime at -70 °C, it remains in Bulb A. The remaining pressure in Bulb A is due to the partial pressures of CO₂ and any residual H₂O(g) or N₂(g) that did not transfer.
5. Conclude what Bulbs A and B contain after equilibrium. Bulb A will contain CO₂(s) and possibly some residual H₂O(g) and N₂(g), while Bulb B will contain condensed H₂O and N₂(g).

Key Concepts

Phase Changes

Phase changes refer to the transitions between solid, liquid, and gas states of matter. In this scenario, understanding sublimation and boiling is crucial, as CO2 sublimates at -78 °C and N2 boils at -196 °C. This means that at the temperatures in bulbs B and C, CO2 will transition from gas to solid, while N2 will transition from gas to liquid, affecting the composition of the gases in bulbs A and B.

Gas Laws

Gas laws describe the behavior of gases under various conditions of temperature and pressure. The ideal gas law (PV=nRT) is particularly relevant here, as it allows us to relate the pressure, volume, and temperature of the gases in the bulbs. When the stopcock between A and B is opened, the gases will redistribute according to these laws, leading to a new equilibrium pressure of 219 mm Hg.

Equilibrium

Equilibrium in a chemical system occurs when the rates of forward and reverse processes are equal, resulting in stable concentrations of reactants and products. In this case, after opening the stopcock, the gases will reach a new equilibrium state between bulbs A and B. Understanding how the gases interact and the impact of temperature on their states is essential for predicting the final contents of the bulbs.