Ch.7 - Thermochemistry

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.7 - Thermochemistry

Problem 35c

Chapter 7, Problem 35c

Suppose that a person eats 2105 Calories per day. Convert this amount of energy into each unit. c. kWh

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Understand that 1 Calorie (with an uppercase C, also known as a kilocalorie) is equivalent to 1000 calories (with a lowercase c).

Recall that 1 calorie is equivalent to 4.184 joules.

Calculate the total energy in joules by multiplying the number of Calories by 1000 to convert to calories, and then by 4.184 to convert to joules.

Remember that 1 kilowatt-hour (kWh) is equivalent to 3.6 million joules (3.6 x 10^6 J).

Convert the energy from joules to kilowatt-hours by dividing the total joules by 3.6 million.

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Key Concepts

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

Calorie Conversion

A Calorie (specifically a kilocalorie) is a unit of energy commonly used in nutrition. It is defined as the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. Understanding how to convert Calories to other energy units is essential for solving energy-related problems.

Energy Units

Energy can be measured in various units, including joules, kilowatt-hours (kWh), and Calories. One kilowatt-hour is the amount of energy consumed by a 1,000-watt appliance running for one hour, equivalent to 3.6 million joules. Familiarity with these units and their conversions is crucial for accurate energy calculations.

Conversion Factors

Conversion factors are numerical values used to convert one unit of measurement to another. For example, to convert Calories to kWh, one must know that 1 Calorie is approximately 0.000293 kWh. Mastery of these factors allows for seamless transitions between different energy units in calculations.

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Conversion Factors

Related Practice

Textbook Question

Convert between energy units. c. 4.99 × 10³ kJ to kWh

Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. Identify each energy exchange as primarily heat or work. a. A rolling billiard ball collides with another billiard ball. The first billiard ball (defined as the system) stops rolling after the collision. b. A book falls to the floor. (The book is the system). c. A father pushes his daughter on a swing. (The daughter and the swing are the system). Identify each energy exchange as primarily heat or work.

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.) b. A balloon expands against an external pressure. (The contents of the balloon is the system.) c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.) Identify energy exchanges as primarily heat or work. Determine whether the sign of E is positive or negative for the system.

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