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.
-Approximately how much heat in kJ was released from the combustion of the 1-g sample?

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.
-Approximately how much heat in kJ was released from the combustion of the 1-g sample?

Quizplus · Accepted Answer

11ecba2d_12f9_863b_a3bf_f766f2867d41_MD0008_00 Calorimetry is a technique used to measure heat transfer from changes in temperature. The amount of heat q required to change the temperature of a substance is the product of its mass m, specific heat c (the amount of heat required to increase 1 g of a substance by 1°C), and the change in temperature ΔT: 11ecba2d_12f9_863c_a3bf_65122b4d17a3_MD0008_00 In the experiment described in the passage, the heat released from the combustion reaction is absorbed by the surrounding water (m = 500 g). The description of a gram calorie (cal) is the definition of water's specific heat: c = 1 cal/(g⋅°C). The maximum temperature change ΔT = 10°C (Figure 1) is due to the total heat released from the combustion reaction. The heat q released in cal is the product of these values (Choice A): 11ecba2d_12f9_863d_a3bf_d7ed71184095_MD0008_00 The value of 5,000 cal of heat energy is converted to kJ using the conversion provided in the passage: 1,000 cal = 4.185 kJ ≈ 4.2 kJ (rounded to two significant digits). 11ecba2d_12f9_863e_a3bf_7f428f82dc35_MD0008_00 This value is closest to 20 kJ. (Choice C) The mass of the water is used in the calorimetry equation because it absorbs the heat from the combustion reaction. If the mass of the sample (1 g) and the incorrect conversion 1 cal ≈ 4.2 kJ are used, q is calculated as 42 kJ. (Choice D) The amount of heat transferred depends on the change in temperature ΔT, not the final temperature reached. If the final temperature of the water (35°C) is incorrectly used, q is calculated as 70 kJ. Educational objective: Calorimetry is a technique used to measure heat transfer from changes in temperature. The specific heat of a substance is the amount of heat required to increase 1 g of a substance by 1°C. The change in heat q is the product of the mass m, the specific heat c, and the change in temperature ΔT: q = mcΔT.

Passage A Student Performed an Experiment to Determine the Energy Content