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Ch.18 - Chemistry of the Environment
All textbooksBrown 14th EditionCh.18 - Chemistry of the EnvironmentProblem 59
Chapter 18, Problem 59

In the following three instances, which choice is greener in each situation? Explain (a) Benzene as a solvent or water as a solvent (b) The reaction temperature is 500 K or 1000 K (c) Sodium chloride as a by-product or chloroform (CHCl3) as a by-product.

Verified step by step guidance
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Step 1: Consider the environmental impact of using benzene versus water as a solvent. Benzene is a volatile organic compound (VOC) and is toxic, posing health risks and environmental hazards. Water, on the other hand, is non-toxic and environmentally benign, making it a greener choice.
Step 2: Evaluate the energy consumption and environmental impact of reaction temperatures. A reaction at 1000 K requires more energy input than at 500 K, leading to higher energy consumption and potentially greater carbon emissions. Therefore, a lower temperature (500 K) is generally greener.
Step 3: Compare the environmental and health impacts of sodium chloride and chloroform as by-products. Sodium chloride (table salt) is non-toxic and widely used, whereas chloroform is a hazardous chemical with potential health risks and environmental concerns. Sodium chloride is the greener by-product.
Step 4: Summarize the greener choices: (a) Water as a solvent is greener than benzene. (b) A reaction temperature of 500 K is greener than 1000 K. (c) Sodium chloride as a by-product is greener than chloroform.
Step 5: Reflect on the importance of considering toxicity, energy consumption, and environmental impact when determining the greener choice in chemical processes.

Key Concepts

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

Solvent Properties

The choice of solvent significantly impacts the environmental footprint of a chemical process. Water is often considered a greener solvent due to its non-toxic nature, abundance, and ability to dissolve a wide range of substances. In contrast, benzene is a volatile organic compound that poses health risks and environmental hazards, making water the preferable choice in terms of sustainability.
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Reaction Temperature and Energy Efficiency

The temperature at which a reaction occurs affects both the energy consumption and the rate of the reaction. Higher temperatures, such as 1000 K, typically require more energy input, which can lead to increased greenhouse gas emissions if fossil fuels are used. Conversely, lower temperatures, like 500 K, are generally more energy-efficient and environmentally friendly, making them a greener option.
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By-products and Environmental Impact

The nature of by-products generated in a chemical reaction can greatly influence its overall environmental impact. Sodium chloride is a common, relatively benign by-product that can be easily managed and disposed of. In contrast, chloroform (CHCl3) is a hazardous substance with potential health risks and environmental concerns, making sodium chloride the greener choice in this context.
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Related Practice
Textbook Question

A reaction for converting ketones to lactones, called the Baeyer–Villiger reaction,

is used in the manufacture of plastics and pharmaceu- ticals. 3-Chloroperbenzoic acid is shock-sensitive, how- ever, and prone to explode. Also, 3-chlorobenzoic acid is a waste product. An alternative process being developed uses hydrogen peroxide and a catalyst consisting of tin deposited within a solid support. The catalyst is readily recovered from the reaction mixture. (a) What would you expect to be the other product of oxidation of the ketone to lactone by hydrogen peroxide?

Textbook Question

In the following three instances, which choice is greener in a chemical process? Explain. (a) A reaction that can be run at 350 K for 12 h without a catalyst or one that can be run at 300 K for 1 h with a reusable catalyst.

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Textbook Question

Suppose that on another planet the atmosphere consists of 17% Kr, 38% CH4, and 45% O2. What is the average molar mass at the surface? What is the average molar mass at an altitude at which all the O2 is photodissociated?