1. Under normal physiological assumptions, one human exhalation contains 5.1 x 1
ID: 738081 • Letter: 1
Question
1. Under normal physiological assumptions, one human exhalation contains 5.1 x 10-2 g ofcarbon dioxide. Assuming 15 breaths per minute per person and a world population of 6.0 x 109
persons, what is the total amount of carbon dioxide released by human respiration in the course
of one year?
2. Glucose oxidation in the human body releases 6 mol of carbon dioxide per mole of glucose.
How many moles of glucose are required to produce the amount of carbon dioxide determined in
question 8?
3. Glucose oxidation has a standard enthalpy of -2803 kJ mol-1. What is the total heat
produced by human respiration over the course of one year?
Explanation / Answer
humans contribute about 3%-4% of atmospheric CO2. But it is that extra CO2 that makes all the difference because the environment was in equilibrium absorbing almost exactly as much CO2 as released, thereby resulting in only very gradual change unless some non-natural source (like us) adds a significant amount (like 3%) over a sustained period of time. Manmade carbon dioxide ("CO2") emissions are much smaller than natural emissions. Consumption of vegetation by animals & microbes accounts for about 220 gigatonnes of CO2 per year. Respiration by vegetation emits around 220 gigatonnes. The ocean releases about 332 gigatonnes. In contrast, when you combine the effect of fossil fuel burning and changes in land use, human CO2 emissions are only around 29 gigatonnes per year. However, natural CO2 emissions (from the ocean and vegetation) are balanced by natural absorptions (again by the ocean and vegetation). Land plants absorb about 450 gigatonnes of CO2 per year and the ocean absorbs about 338 gigatonnes. This keeps atmospheric CO2 levels in rough balance. Human CO2 emissions upsets the natural balance. About 40% of human CO2 emissions are being absorbed, mostly by vegetation and the oceans. The rest remains in the atmosphere. As a consequence, atmospheric CO2 is at its highest level in 15 to 20 million years. A natural change of 100ppm normally takes 5,000 to 20,000 years.
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