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Units of Energy

Q. The evaporation of four grams of water at 100°C utilizes 9027 J heat. (a) Express this amount of heat in calories and kJ. (b) Is the evaporation process endothermic or exothermic? When water evaporates and transforms into a gas, heat energy is ___ by the system. Thus, the process of evaporation is ___ (c) Will the heat transfer value (q) be positive or negative for this reaction? In the evaporation of water, the system (water) ___ heat. Therefore, q will be ___.

Solved • Jul 18, 2019

Units of Energy

Q. Two friends, Pamela and Elaine, compared snack items they planned to enjoy during a work break. Pamela's snack was a small bag of shortbread cookies composed of 2.5 grams fat, 18 grams carbohydrates, and 2.3 grams protein. Elaine had a bag of popcorn composed of 2.7 grams of fat, 29 grams of carbohydrates, and 3.6 grams protein. Nutrient: Fuel value (kJ/g) Carbohydrate: 17 Fat: 38 Protein: 17 (a) Using the fuel values provided, calculate the number of calories in each person's snack. Pamela's snack ___ Cal Elaine's snack ___ Cal (b) Suppose the friends took a 15-minute walk after snacking. If Pamela burned 45 calories and Elaine expended 48 calories, who had the smaller net gain of calories after snacking and walking?

Solved • Jul 18, 2019

Units of Energy

Q. A train has a mass of 16796 kg. If its velocity is 14.7 m/s then how much kinetic energy does it have in joules? Round the answer to 3 significant figures. Include the correct unit with your answer.

Solved • Jun 7, 2019

Units of Energy

Q. It takes somewhere between 227-342 MJ of energy to produce 1.00 kg of Al from bauxite. Let’s average the number span to produce one number for the following calculations, 284.5 MJ. How much energy would it take to produce the Al for one can? Assume the mass of Al used for the can is 14.0g. If the can was made from 100% recycled Al, how much energy would it take?

Solved • Jun 4, 2019