How Does Fuel Make So Much CO₂?

Written By Teacher: Emily Rogers

Emily has a bachelor’s degree in English and French and a master’s degree in library and information science. She spent seven years teaching information evaluation and research skills as a school librarian in K-8 public schools. As a lifelong resident of Southern Louisiana, Emily has a particular interest in how climate change affects coastal regions. She hopes to connect educators with resources that will help them to teach their students about the disproportionately adverse effects of climate change on historically marginalized communities.

Students often hear about the environmental impact of burning fossil fuels but may not understand the underlying chemistry that makes this process problematic. They may be surprised to learn that a single ton of fossil fuel can produce several tons of CO2. Teachers can help demystify the science behind this phenomenon by introducing students to the properties of carbon as well as the carbon cycle. Once students understand the basics, engage them in this interactive activity that will give them the chance to role-play carbon molecules. As educators, we can use this topic to foster curiosity, deepen scientific literacy, and encourage students to consider the broader implications of the energy choices we make every day.

Written By: MIT Environmental Solutions Initiative

The MIT Climate Change Engagement Program, a part of MIT Climate HQ, provides the public with nonpartisan, easy-to-understand, and scientifically-grounded information on climate change and its solutions.

Burning fossil fuels such as coal, natural gas, and oil creates a troubling amount of carbon dioxide (CO2). For example, says Yogesh Surendranath, Paul M Cook Career Development Associate Professor of Chemistry at MIT, burning a commonly used kind of coal called anthracite emits around 2.6 tons of CO2 for every ton of coal. But how can this be? If atoms are not magically created or destroyed, how can burning a ton of fuel create more than a ton of CO2?

The answer is deceptively simple, Surendranath explains. Carbon dioxide is made of one carbon atom and two oxygen atoms. The carbon comes from the coal, but the oxygen comes from the air around it; during combustion, they react to create CO2. That oxygen’s extra mass is what allows one ton of fuel to produce more than a ton of CO2.

Exactly how much CO2 a fuel emits depends on its molecular structure. Suppose, Surendranath says, that you could burn a perfect lump of coal made of 100 percent carbon. Each of its carbon atoms has an atomic weight of approximately 12, owing to its six protons and six neutrons. When the carbon combines with two oxygen atoms, each with an atomic weight of 16, a CO2 molecule with a weight of 44 is created. The math tells you that for every ton of pure carbon burned, about 3.66 tons of CO2 is created.