Passage
A student performed an experiment to determine the energy content of a sample of potato chips. The chips were blended and then freeze-dried to remove moisture from the sample. Freeze-drying, or lyophilisation, is the preferred dehydration process for food calorimetry due to its minimal impact on nutritional content. Lyophilisation removes water from frozen food samples at low pressure through sublimation. The water is later collected in a cooled condensation chamber to prevent damage to any electric components.After freeze-drying, the sample was ground into a dry homogenous powder. A 1-g sample of the powder was placed in a bomb cell, an enclosed steel-walled container, and pressurized to 25 atm with pure oxygen to ensure complete combustion. The bomb cell was submerged in 500 g of water at room temperature (25°C) in an enclosed and thermally insulated calorimetry device. The sample was combusted using an electric fuse. The temperature of the surrounding water was measured with a glass thermometer every 30 s for several minutes (Figure 1) .
Figure 1 Temperature of the water in the bomb calorimeterThe energy content of food is given in units of dietary calories (Cal) , which is equal to 4.185 kJ, or 1,000 gram calories (cal) . A gram calorie is the amount of energy required to increase 1 g of water by 1°C.
Adapted from Jumpertz R, Venti CA, Le DS, et al., Food label accuracy of common snack foods. Obesity 2013 Wiley-Blackwell.
-What is the order of the phase changes of water throughout the lyophilisation process after freezing?

Question

Passage
A student performed an experiment to determine the energy content of a sample of potato chips. The chips were blended and then freeze-dried to remove moisture from the sample. Freeze-drying, or lyophilisation, is the preferred dehydration process for food calorimetry due to its minimal impact on nutritional content. Lyophilisation removes water from frozen food samples at low pressure through sublimation. The water is later collected in a cooled condensation chamber to prevent damage to any electric components.After freeze-drying, the sample was ground into a dry homogenous powder. A 1-g sample of the powder was placed in a bomb cell, an enclosed steel-walled container, and pressurized to 25 atm with pure oxygen to ensure complete combustion. The bomb cell was submerged in 500 g of water at room temperature (25°C) in an enclosed and thermally insulated calorimetry device. The sample was combusted using an electric fuse. The temperature of the surrounding water was measured with a glass thermometer every 30 s for several minutes (Figure 1) .

Figure 1 Temperature of the water in the bomb calorimeterThe energy content of food is given in units of dietary calories (Cal) , which is equal to 4.185 kJ, or 1,000 gram calories (cal) . A gram calorie is the amount of energy required to increase 1 g of water by 1°C.
Adapted from Jumpertz R, Venti CA, Le DS, et al., Food label accuracy of common snack foods. Obesity 2013 Wiley-Blackwell.
-What is the order of the phase changes of water throughout the lyophilisation process after freezing?

Quizplus · Accepted Answer

11ecba2d_12f9_fb6f_a3bf_49205e5f6050_MD0008_00 The phases of matter describe the uniform physical state of the matter's molecules, and include solid, liquid, and gas: Molecules in a solid are tightly packed in an ordered structure and retain a fixed shape. Molecules in a liquid move past each other (but stay close together) and assume the shape of their container at a fixed volume. Molecules in a gas move past each other, can be well separated, and assume the shape and volume of their container. The phase of matter depends on the temperature and pressure of its environment, and therefore changes in pressure and/or temperature can cause phase changes. According to the passage, the lyophilisation process begins with a frozen sample, so the water in the sample starts out in its solid phase. Afterward, the frozen water is sublimated at low pressures, and sublimation is the phase change of a solid directly to a gas. In the last step, the sublimated water vapor (gas) is collected in a condensation chamber, and condensation is the phase change of a gas to a liquid. (Choices B and D) The phase change from a gas to a solid is deposition, and the change from a liquid to a solid is freezing. There is no indication that the water returned to a solid at the end of the lyophilisation process. (Choice C) The phase changes from solid to liquid and liquid to gas are melting and vaporization, respectively. The sublimation of water is the direct transition from its solid phase to its gas phase without entering the intermediary liquid phase. Educational objective: The phases of matter describe the physical state of the matter's molecules, and include solid, liquid, and gas. Sublimation is the phase change from solid to gas, and condensation is the phase change from gas to liquid.

Passage A Student Performed an Experiment to Determine the Energy Content