3. Coal: Energy and Matter

3. Coal: Energy and Matter

Notes to faculty

Outcomes: Students understand that energy is not a physical entity (it is separate, but linked to matter), they can trace energy from chemical bond energy to mechanical and heat energy, and thus that energy comes in different forms. They better understand that carbon in fossil fuels like coal is "old" organic carbon that originated from photosynthesis, but has protected from decomposition for millions of years.

What students do: The exercise forces students to distinguish between energy and matter (carbon) transformations in coal generation and oxidation. The “Directions” are divided into two sections – Energy Flow Diagrams and Carbon Flow Diagrams. Using simple box-and-arrow diagrams students are asked a very directed set of questions designed to expose possible misconceptions about what fossil fuel energy is and the relationship between matter and energy in fossil fuel oxidation and creation.

What to pay particular attention to: This is another example of paying close attention to exactly what students are saying and writing. For instance, in interviews students say “fuels are burned up”, meaning that the matter in the fuel disappears, although you could interpret this as oxidation.

Logistics: There are many ways you could use these questions – e.g. as homework to assess student understanding, as groupwork leading to a discussion and lecture about this topic, and as ‘clicker questions’.

Units and quantitative skills: Box-and-arrow diagrams; moving between abstract diagrams and words/phrases.

• Principles: Conservation of Matter: Carbon is conserved and can be traced (Specifically, fossil fuel burning pulls from huge pool of C sequestered from the ecosystem for millions of years). Conservation of Energy: Energy is conserved although the biosphere is open with respect to light energy; energy and matter are related (energy can cycle through ecosystems in conjunction with matter as chemical bond energy) but energy and matter are not interchangeable.

• Processes: Generation (photosynthesis), Oxidation of fossil fuels.

• Scale & Time: Relationship between molecular, organismal, and ecosystem processes of photosynthesis and oxidation of fossil fuels; long term and short term pools.

• Forms & Representations: Ecosystem/ global matter & energy flow; different forms of energy as light, fossil fuels, heat.

Student Directions

As you know, when coal is burned in a stove, heat is released into the surrounding area (for instance, a room). Using what you know about box-and-arrow diagrams and and matter (carbon) and energy flow (movement) in ecosystems, address the following:

1. Burning of coal: Below is a box-and-arrow diagram showing conversion of energy in coal to energy in the form of heat in the room. Discuss the diagram below with your group and make sure you understand what it is meant to show. Be sure to discuss what the phrase “is converted to” means. Write down any questions.

ENERGY FLOW DIAGRAMS

When coal is burned, the

is converted to

1. Formation of coal: Coal is a fossilized form of plant matter; coal deposits were formed about 350 million years ago when plants living then were preserved in mud where there was little or no oxygen. Where did the energy in the coal come from? Draw a box and arrow diagram like the one above showing the source of the energy for coal in the box on the left and the process involved in this energy transformation below the arrow.

Write down any questions or confusions you have.

1. Now, work with box-and-arrow diagrams showing transformations of carbon in the processes of coal formation and burning. First, discuss the representation directly below with your group to make sure you understand what it is meant to show. Pay special attention to the phrase “is transformed into” to make sure you understand exactly what this means. Write down any questions.

CARBON FLOW DIAGRAMS

When coal is burned:

is transformed into

1. Formation of coal: Where did the carbon in the coal come from in the first place? Again, write the source of the carbon in the left-side box and the process below the arrow. Coal is the largest worldwide source* of CO2 and thus contributes greatly to climate change. Therefore, the molecules of CO2 now in our atmosphere were last in the world’s atmosphere when? Write down any questions you have.

* Source: Intergovernmental Panel on Climate Change (IPCC)

1. Comparison of conversion of energy and transformation of carbon:

• The law of conservation of energy states that energy cannot be created or destroyed, it can only be changed from one form to another.
• The law of conservation of matter is that matter cannot be created or destroyed, although it may be rearranged.

Using the coal diagrams above as examples, explain these two important laws of physics and chemistry.