Opening a Compost Pile

Opening a compost pile on a chilly morning allows “steam” to escape and a thermometer stuck into a compost pile near the surface and deep into the pile, shows radically different temperatures on a spring day.

• Why the temperature difference? Where does the heat and “steam” come from?

• Does the material in the compost make a difference?
• How do other factors affect the temperature? (moisture, time, ambient temperature, sunlight)

Students could:

• Watch the video without sound and speculate what variables were changed.
•  Use example reactants and products of aerobic composting to calculate the enthalpy of breaking down plant material (glucose and oxygen to carbon dioxide and water. Use provided resources for background on Hess’s Law and Enthalpy of Formation.
• Compare to anaerobic respiration chemical reactions examples.
• Complete class investigation at the local compost facility or using grass clippings and/or food scraps from the school to set up experiments with controlled variables. Compare heat released, rate of decay, etc. 
• Explore endothermic and exothermic reactions by comparing meat temperature recommendations to bring in how heat is important to destroying potentially dangerous bacteria, parasites, molds, etc. to make the compost safe for gardens. Tie to endothermic reactions that denature proteins. Contrast aerobic vs anaerobic respiration, energy released and methane production; why compost needs to be turned.

• Washington State University | Compost Fundamentals: Background on the process of composting, including elements involved, heat produced and bacterial activity.
• Cornell University | Cornell Composting: Composting in Schools: Links to their compost information site and online quiz that can be used for introduction or review.
• Chemistry Libre Texts | 5.6: Hess’s Law: Background on Hess’s Law to calculate the energy of a reaction.
• Chemistry Libre Texts | 5.7: Enthalpy of Formation: Background on using enthalpies of formation to calculate reaction enthalpy.