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Chapter 11: Problem 80

Freeze-dried coffee is prepared by freezing brewed coffee and then removing the ice component with a vacuum pump. Describe the phase changes taking place during these processes.

Short Answer

Expert verified
The phase changes taking place during the freeze-drying of coffee are: liquid to solid when the coffee is frozen, and solid to gas when the ice is removed with a vacuum pump.

Step by step solution

01

Identifying the Initial Phase

The brewed coffee initially is in its liquid form.
02

Phase Change 1 - Freezing the Coffee

When the liquid (brewed coffee) is frozen, it changes its state from a liquid to a solid (ice). This is the first phase change that occurs. The molecules of coffee slow down and form a relatively fixed position as the temperature drops.
03

Phase Change 2 - Removing the Ice Component

Next, the ice (frozen coffee) is exposed to a vacuum pump. Under this low-pressure environment, the solid ice directly transitions to a gas in a process known as sublimation, skipping the liquid phase entirely. The water molecules in the ice gain enough energy to move from a solid state directly to a gas state.
04

Summary of Phase Changes

To sum up, the brewed coffee undergoes phase changes from being a liquid (coffee) to becoming a solid (ice), and then directly changes to a gas (water vapor) during the freeze-drying process.

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Most popular questions from this chapter

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