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Green chemistry industry icon

Green chemistry industry icon (Petmal, iStockphoto)

STEM in Context

Green Chemistry 101

Rachel Hems with files from Let's Talk Science

Summary

Green chemistry is a field that looks at the sustainability of products and processes designed by people.

Do you recycle? Compost? Turn off the lights when you leave a room? If so, you’re practicing environmental sustainability. You’re recognizing that our planet has limited resources, and you’re supporting its long-term health.

Chemists design all kinds of products, including plastics, pesticides and pharmaceuticals. Historically, when chemists have designed products, they would focus on the product’s usefulness. They didn’t necessarily think about sustainability. In fact, a lot of these products and the processes used to make have actually turned out to be harmful for the environment! So have the processes used to make them. That’s why the field of green chemistry has been growing over the past 30 years.

Chemists use green chemistry to look at the sustainability and environmental impacts of manufactured chemical products and processes. Green chemists think about a chemical’s impact from the laboratory, to the disposal site, to the environment where it is released. One way they can evaluate these impacts is with the 12 Principles of Green Chemistry

Let’s look at three of these principles in detail.

Graphic that shows the 12 guiding principles of green chemistry
Graphic that shows the 12 guiding principles of green chemistry (© 2019 Let’s Talk Science).

 

Infographic_text_version

The twelve principles of green chemistry include waste prevention, atom economy, less hazardous chemical synthesis, designing safer chemicals, safer solvents, design for energy efficiency, use of renewable feedstocks, reduce derivatives, catalysts, design for degradation, real-time pollution prevention and safer chemistry for accident prevention.

 

The Prevention of Waste 

This principle actually applies to many aspects of life, both in and outside of the laboratory. For example, it’s the first rule of the Three R’s: reduce. It’s important to dispose of waste properly. But it’s even better to reduce the amount of waste being produced in the first place. 

You might apply this principle by trying to produce less garbage at home. Chemists apply this principle by trying to produce less chemical waste.

You might not think of your car as something that produces waste, but it does. Inside a car’s engine, fuel and oxygen from the air undergo a chemical reaction called combustion. The combustion reaction produces the energy needed for the car to move. But it also produces some harmful byproducts. For example, combustion produces carbon monoxide (CO), which is poisonous. It also produces volatile organic compounds (VOCs), nitrogen oxides (NOx), and unburnt hydrocarbons (HC). All of these contribute to smog. Too much smog in the environment can give people respiratory illnesses.

Cross-section of a catalytic converter
Cross-section of a catalytic converter. The orange grid structures have surfaces covered in catalytic elements (Source: mipan via iStockphotos).

Luckily, cars contain a piece of technology that helps prevent the production of harmful chemicals. It’s called a catalytic converter. While the car is running, a catalytic converter chemically changes these pollutants into less harmful molecules before they’re released from the car’s tailpipe. Examples of these less harmful molecules are oxygen (O2), nitrogen (N2), carbon dioxide (CO2), and water (H2O).  

Did you know?

There are many ways that air pollution can actually cost people money. For example, people might miss work or need to buy medicine if they get sick from pollution. If they own a home in a polluted area, that home might become worth less money over time. In fact, researchers estimated that air pollution cost Canadians over $36 billion in 2015

Atom Economy 

Imagine you are making cookies and you measure out two cups of flour. You only end up using one cup of flour to make the cookies, so you throw out the other cup. That would be very wasteful!

Sadly, this type of waste can happen when chemists make various products through chemical reactions. Green chemists aim to reduce this waste by looking at atom economy. Atom economy asks the questions, “What percent of atoms from the reactants are incorporated into the product? What percent of atoms are wasted?” 

For example, the synthesis reaction that occurs during photosynthesis in plants leads to two products: glucose (C6H12O6) and oxygen gas (O2). If the glucose were the desired product, then the oxygen gas would be considered a wasted product. 

Atom economy of photosynthesis

Step 1: Identify the reactants and products. For photosynthesis this would be:
CO2 + H2O ---> C6H12O6 + O2

Step 2: Balance the chemical equation. For photosynthesis this would be:
6CO2 + 6H2O ---> C6H12O6 + 6O2

Step 3: Determine the masses of reactants and products based on atomic mass
CO2 = 6(44) = 264            C6H12O6 = 180
H2O = 6(18) = 108            6O2 = 6(32) = 192    
Total mass of reactants = 372    Total mass of products = 372

Step 4: Determine the percentage of desired product (C6H12O6) (mass of desired product/total mass of products) x 100 

180/372*100 = 48.4%

 

Atom Economy - Green Chemistry Principle #2 (2014) by GreenChemUofT (3:57 min.).

 

Ideally, products should have a high atom economy. Most of the ingredients added during a chemical process should be used to make the final product.

You might have an example of green chemistry in your medicine cabinet: ibuprofen, the active ingredient in Advil and Motrin. The original method for making ibuprofen was wasteful and inefficient. Of the atoms used to make the product, only 40% made it into the final product. In the 1990s, the manufacturer developed a new process that incorporated a few of the principles of green chemistry. Since the changes, 77% now make it into the final product!  Changes like this earned the manufacturer a Green Chemistry Challenge Award in the United States in 1997. 

Catalytic Ingredients

A catalyst is a substance that helps a chemical reaction happen or makes it go faster. Catalysts can lead to reactions that produce less waste or have a greater atom economy.

Take the example of the catalytic converter that can be found in a car. As its name suggests, the converter contains a catalyst. The catalyst causes the reaction that converts some of those toxic gases into less harmful ones.

The elements platinum, palladium and rhodium are often used as catalysts
The elements platinum, palladium and rhodium are often used as catalysts (Let's Talk Science using image by Periodictableru [CC BY], Hi-Res Images of Chemical Elements [CC BY and Alchemist-hp (talk) www.pse-mendelejew. dederivative work: Purpy Pupple [CC BY-SA 3.0] Wikimedia Commons (Pt, Pd, Rh)).


 As an added bonus, catalysts aren’t used up in a reaction! That means they can be continually reused without being replaced.

Did you know?

Vehicles with Diesel engines use different catalytic converters than vehicles with gasoline engines.

The principles of green chemistry in industry and at home 

Green chemistry principles are important. They help chemists make some of the products you use every day less harmful to the environment. They can also help manufacturers save money. That’s because green chemistry means more efficient processes with less wasted material, less energy used, and less hazardous waste to clean up!

You may not be a green chemist yourself. But you can still apply sustainable green chemistry practices in your life! For example:

  • Reduce the waste you produce by recycling or composting when possible
  • Try to choose products that are made using green chemistry practices
  • Dispose of harmful waste in a proper way (for example: recycle batteries and electronics at designated locations, and return unused medicine to your pharmacy instead of pouring it down the drain)

Finally, you can make a big impact when you go shopping. Buy products that don’t have a lot of packaging, are less harmful to the environment, and are made with sustainability in mind!

Did you know?

Electric cars are an example of a product made with sustainability in mind. More and more Canadians are buying them. In fact, the Government of British Columbia has announced that all vehicles sold there after 2040 must produce zero emissions.

Starting Points

Connecting and Relating
  • Are you concerned about waste in your daily life? Are you conscious of the chemicals you put down the drain each day? 
  • What things do you do to recycle, reduce or reuse to help decrease the amount waste you produce? 
  • Do you think that the small changes you make can make a difference in terms of sustainability? Why or why not?
Connecting and Relating
  • Are you concerned about waste in your daily life? Are you conscious of the chemicals you put down the drain each day? 
  • What things do you do to recycle, reduce or reuse to help decrease the amount waste you produce? 
  • Do you think that the small changes you make can make a difference in terms of sustainability? Why or why not?
Relating Science and Technology to Society and the Environment
  • Why might manufacturing companies be interested in implementing green chemistry processes? 
  • How could the increased use of green chemistry principles affect the environment?
Relating Science and Technology to Society and the Environment
  • Why might manufacturing companies be interested in implementing green chemistry processes? 
  • How could the increased use of green chemistry principles affect the environment?
Exploring Concepts
  • Define green chemistry. 
  • What is a catalyst? 
  • What specific principles of green chemistry from the chart can be applied to products like biodegradable plastic and microplastics? 
Exploring Concepts
  • Define green chemistry. 
  • What is a catalyst? 
  • What specific principles of green chemistry from the chart can be applied to products like biodegradable plastic and microplastics? 
Nature of Science/Nature of Technology
  • What social pressures, big questions and problems are influencing the science of chemistry currently?
Nature of Science/Nature of Technology
  • What social pressures, big questions and problems are influencing the science of chemistry currently?
Media Literacy
  • Can you think of a green chemistry principle or process that has been reported in the media? If so, what was it? 
  • Do you think advances in chemistry or green chemistry get as much media time as other scientific fields? Why or why not?
Media Literacy
  • Can you think of a green chemistry principle or process that has been reported in the media? If so, what was it? 
  • Do you think advances in chemistry or green chemistry get as much media time as other scientific fields? Why or why not?
Teaching Suggestions
  • This article supports teaching and learning in chemistry and environmental studies for topics such as catalysts, combustion, stoichiometry, redox reactions and sustainability. Concepts explored include green chemistry, catalyst, and atom economy.
  • After reading this article students could complete a Concept Definition Web learning strategy to help develop their understanding of the term Green Chemistry. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [.pdf] formats. 
  • To explore the Science/Technology/Engineering/Math of green chemistry, students could conduct research into one type of green chemistry initiative, such as using biopesticides to replace conventional pesticides, or converting waste biomass and waste cellulose into various products, such as animal foods, fuels and industrial chemicals. Once students have some understanding of a chosen initiative, they could complete a Pros & Cons Organizer learning strategy to see where the initiative may have particular strengths and weaknesses. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats.
  • Students could also consider the implementation and impacts of a particular green chemistry initiative from different points of view and conduct an Issues & Stakeholders learning strategy. Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats.
Teaching Suggestions
  • This article supports teaching and learning in chemistry and environmental studies for topics such as catalysts, combustion, stoichiometry, redox reactions and sustainability. Concepts explored include green chemistry, catalyst, and atom economy.
  • After reading this article students could complete a Concept Definition Web learning strategy to help develop their understanding of the term Green Chemistry. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [.pdf] formats. 
  • To explore the Science/Technology/Engineering/Math of green chemistry, students could conduct research into one type of green chemistry initiative, such as using biopesticides to replace conventional pesticides, or converting waste biomass and waste cellulose into various products, such as animal foods, fuels and industrial chemicals. Once students have some understanding of a chosen initiative, they could complete a Pros & Cons Organizer learning strategy to see where the initiative may have particular strengths and weaknesses. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats.
  • Students could also consider the implementation and impacts of a particular green chemistry initiative from different points of view and conduct an Issues & Stakeholders learning strategy. Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats.

Learn more

Green Chem UofT

Students at the University of Toronto have created videos for each of the 12 Principles of Green Chemistry!

Air Pollution in Canada: Real-time Air Quality Index Visual Map

A real-time map to visual the air quality of a given region.

An Example of Making Sustainable Choices: Bring Your Own Coffee Cup (2013)

An infographic demonstarting the environmental impact of using paper cups.

Green Centre Canada

A Canadian company that helps link green chemistry research with industry needs

Vehicle Emissions Primer (2014)

A Let's Talk Science Backgrounder by Sylvie Trottier about vehicle emissions.

References

American Chemical Society. (n.d.). 12 principles of green chemistry

American Chemical Society. (n.d.). Green chemistry history

American Chemical Society (n.d.). What is green chemistry?

International Institute for Sustainable Development. (2017). Costs of pollution in Canada.

Kahlon, A., & Tang, T. (2018). Catalytic converters. LibreTexts.

Nice, K., & Bryant, C. How catalytic converters work. HowStuffWorks.