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.
-For the combustion reaction of the sample into CO₂ (g) and H₂O (g) in the bomb cell:

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.
-For the combustion reaction of the sample into CO₂ (g) and H₂O (g) in the bomb cell:

Quizplus · Accepted Answer

11ecba2d_12f8_74c4_a3bf_af73da44491b_MD0008_00 Enthalpy (H) is the thermodynamic quantity that measures the energy stored in a chemical bond, and ΔH is the net amount of energy (heat) released or absorbed from the formation and destruction of chemical bonds in a reaction. Energy is released as heat if the enthalpy of the products is lower than the enthalpy of the reactants, and ΔH is negative (exothermic). Because the temperature of the surroundings (water) increases in the combustion of the sample, heat is released and therefore ΔH is negative. Entropy (S) is the thermodynamic quantity that measures the disorder of a substance (or system). Solids have relatively low entropy because the structure of the molecules is ordered and their motion is more constrained. Gases have relatively high entropy because the molecules are disordered and their motion is less constrained. Because the gaseous products of the reaction are more disordered than the solid powdered sample, disorder increases and therefore ΔS is positive. (Choices A and D) Although the enthalpy (heat) of the surroundings increases, ΔH describes the reaction. ΔH would be positive (endothermic) if energy is absorbed in a chemical reaction. (Choice B) ΔS would be negative if disorder decreases (order increases). Educational objective: Enthalpy (H) is a measure of bond energy, and a change in the enthalpy of a reaction results in the release or absorption of heat. Entropy (S) is a measure of disorder, and it is highest in gases and lowest in solids due to their respective molecular structures. In the combustion of a solid to a gas, heat is released (ΔH is negative) and the products are more disordered (ΔS is positive).

Passage A Student Performed an Experiment to Determine the Energy Content