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Lesson · Grade 11 · Chemistry

Green Chemistry: Designing Out Waste and Harm

  • Grade 11
  • Chemistry
  • 1 min 37 s
  • British Columbia
  • BC11-SC-35

A labelled process diagram changes step by step from an older design (crude oil, a harmful solvent, high temperature, lots of waste) into a green one. It uses renewable plants, water or supercritical CO₂ as the solvent, a reusable catalyst and a lower temperature. Along the way it explains atom economy with a word formula and a product-versus-waste bar, and it ends on the idea that green chemistry prevents waste and harm from the start rather than cleaning up afterwards.

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In one sentence

The question this lesson answers

How can we make useful chemicals without making waste and harm?

Here is a chemical process: starting materials, called reactants, go into a reaction, which makes the product we want.

Transcript

What the lesson says

How can we make useful chemicals without making waste and harm?

Here is a chemical process: starting materials, called reactants, go into a reaction, which makes the product we want.

In an older design, the reactants come from crude oil and react in a harmful solvent, the liquid they dissolve in, at a high temperature.

It also makes a lot of waste, which must be cleaned up.

Green chemistry designs out waste and harm from the start, because preventing waste is better than cleaning it up.

Atom economy is the mass of the product we want, divided by the total mass of the reactants, times 100 percent.

In the older design, much of the reactants' mass ends up as waste. A green design picks reactions where more atoms end up in the product.

Use safer solvents, such as water or supercritical carbon dioxide.

Supercritical carbon dioxide is held above 31 degrees Celsius and at high pressure. It is used to decaffeinate coffee.

Add a catalyst, which speeds up a reaction without being used up, so it can be used again.

With a catalyst, the reaction can run at a lower temperature, which saves energy.

And use renewable starting materials, such as plants, which can be grown again, instead of crude oil, which will run out.

Green chemistry designs out waste and harm from the start, instead of cleaning up afterwards.

Curriculum

Where this fits

British Columbia, Grade 11

Chemistry 11, Reactions: green chemistryBC11-SC-35

Previous: Why Food Browns When It Cooks

The outcomes and strands follow the British Columbia curriculum.

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