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Ch.7 - Thermochemistry
Chapter 7, Problem 36d

A particular frost-free refrigerator uses about 705 kWh of electrical energy per year. Express this amount of energy in each unit. d. Cal

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Identify the conversion factor between kilowatt-hours (kWh) and calories (Cal). Note that 1 kWh = 3.6 x 10^6 J and 1 Cal = 4184 J.
Convert the energy from kilowatt-hours to joules using the conversion factor: Energy (J) = Energy (kWh) x 3.6 x 10^6 J/kWh.
Use the conversion factor between joules and calories to convert the energy from joules to calories: Energy (Cal) = Energy (J) / 4184 J/Cal.
Perform the calculation to find the energy in calories.
Ensure the units are consistent and the conversion is correct by checking each step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Energy Units

Energy can be measured in various units, including kilowatt-hours (kWh) and calories (Cal). A kilowatt-hour is the amount of energy consumed when a device uses one kilowatt of power for one hour. Understanding how to convert between these units is essential for solving energy-related problems.
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Conversion Factors

To convert energy from one unit to another, specific conversion factors are used. For instance, 1 kWh is equivalent to approximately 860 Cal. Knowing these conversion factors allows for accurate calculations when expressing energy in different units.
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Thermodynamics

Thermodynamics is the branch of physics that deals with heat and energy transfer. In the context of refrigerators, it is important to understand how energy is consumed and transformed, as this relates to the efficiency and operation of the appliance. This knowledge aids in comprehending the significance of energy consumption figures.
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Suppose that a person eats 2105 Calories per day. Convert this amount of energy into each unit. c. kWh

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Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative ΔEsys? a. The internal energy of the system increases and the internal energy of the surroundings decreases. b. The internal energy of both the system and the surroundings increases. c. The internal energy of both the system and the surroundings decreases. d. The internal energy of the system decreases and the internal energy of the surroundings increases.

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Textbook Question

Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.)

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