Textbook Question
A watt is a measure of power (the rate of energy change) equal to 1 J/s. (a) Calculate the number of joules in a kilowatt-hour.
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Ch.1 - Introduction: Matter, Energy, and Measurement
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement177
- Ch.2 - Atoms, Molecules, and Ions231
- Ch.3 - Chemical Reactions and Reaction Stoichiometry216
- Ch.4 - Reactions in Aqueous Solution189
- Ch.5 - Thermochemistry175
- Ch.6 - Electronic Structure of Atoms168
- Ch.7 - Periodic Properties of the Elements150
- Ch.8 - Basic Concepts of Chemical Bonding177
- Ch.9 - Molecular Geometry and Bonding Theories200
- Ch.10 - Gases179
- Ch.11 - Liquids and Intermolecular Forces113
- Ch.12 - Solids and Modern Materials154
- Ch.13 - Properties of Solutions157
- Ch.14 - Chemical Kinetics199
- Ch.15 - Chemical Equilibrium128
- Ch.16 - Acid-Base Equilibria164
- Ch.17 - Additional Aspects of Aqueous Equilibria163
- Ch.18 - Chemistry of the Environment105
- Ch.19 - Chemical Thermodynamics164
- Ch.20 - Electrochemistry171
- Ch.21 - Nuclear Chemistry122
- Ch.22 - Chemistry of the Nonmetals82
- Ch.23 - Transition Metals and Coordination Chemistry79
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry16
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 1, Problem 42b
A watt is a measure of power (the rate of energy change) equal to 1 J/s. (b) An adult person radiates heat to the surroundings at about the same rate as a 100-watt electric incandescent light bulb. What is the total amount of energy in kcal radiated to the surroundings by an adult over a 24 h period?
Verified step by step guidance1
Understand that power is the rate of energy transfer, and 1 watt is equal to 1 joule per second (1 W = 1 J/s).
Calculate the total energy in joules radiated by the person over 24 hours. Since the person radiates energy at a rate of 100 watts, multiply 100 J/s by the total number of seconds in 24 hours (24 hours * 60 minutes/hour * 60 seconds/minute).
Convert the total energy from joules to kilocalories. Use the conversion factor: 1 kcal = 4184 J.
Perform the conversion by dividing the total energy in joules by 4184 J/kcal to find the energy in kilocalories.
Summarize the process: You have calculated the total energy radiated by an adult over 24 hours in kilocalories by first finding the energy in joules and then converting it to kilocalories.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Power and Energy Conversion
Power is defined as the rate at which energy is transferred or converted, measured in watts (W), where 1 W equals 1 joule per second (J/s). To find the total energy produced over time, one can multiply power by time. In this case, the energy radiated by the adult can be calculated by converting the power output (100 W) into energy over a 24-hour period.
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Conversion Factors
Time Conversion
To calculate energy over a specific time frame, it is essential to convert the time into seconds, as power is measured in joules per second. For 24 hours, this conversion involves multiplying 24 hours by 3600 seconds per hour, resulting in a total of 86,400 seconds. This total time will be used in the energy calculation.
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Energy Units and Conversion to kcal
Energy can be expressed in various units, including joules (J) and kilocalories (kcal). To convert joules to kilocalories, one must use the conversion factor where 1 kcal equals 4184 J. After calculating the total energy in joules, dividing by 4184 will yield the equivalent energy in kilocalories, which is a more common unit for measuring energy in biological contexts.
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Related Practice
Textbook Question
If on a certain year, an estimated amount of 4 million metrictons (1 metric ton = 1000 kg) of nitrous oxide 1N2O2 wasemitted worldwide due to agricultural activities, express thismass of N2O in grams without exponential notation, usingan appropriate metric prefix.
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Textbook Question
Use of the British thermal unit (Btu) is common in some types of engineering work. A Btu is the amount of heat required to raise the temperature of 1 lb of water by 1°F. Calculate the number of joules in a Btu.
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Textbook Question
Indicate which of the following are exact numbers: (a) the mass of a 3- by 5-in. index card, (b) the number of ounces in a pound, (c) the volume of a cup of Seattle's Best coffee, (d) the number of inches in a mile, (e) the number of microseconds in a week, (f) the number of pages in this book.
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Textbook Question
Indicate which of the following are exact numbers: (a) the mass of a 32-oz can of coffee, (b) the number of students in your chemistry class, (c) the temperature of the surface of the Sun, (d) the mass of a postage stamp, (e) the number of milliliters in a cubic meter of water, (f) the average height of NBA basketball players.
Textbook Question
What is the number of significant figures in each of the following measured quantities? (b) 3ⅹ10-6 m
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