Chapter 17, Problem 1P

Global Carbon Dioxide Cycling Expressed as Human Equivalents

If 3 x 1014 kg of CO² are cycled through the biosphere annually, how many human equivalents (70-Kg people composed of 18% carbon by weight) could be produced each year from this amount of CO₂?

Interpretation Introduction

Interpretation: The number of human equivalents should be determined which could be produced each year from the given amount of carbon dioxide.

Introduction: The biochemical cycle of carbon is the process in which carbon is cycled among the geosphere, hydrosphere, pedosphere, biosphere and atmosphere of the earth. The main form of carbon in the atmosphere is CO₂. CO₂ is a greenhouse gas and recent attempts were made to reduce the amount of which in the atmosphere.

Explanation of Solution

A human is made of 18% of carbon.

  $\frac{18}{100}\times 70\text{ kg=12}\text{.6 kg}$

Therefore, a 70 kg man has 12.6 kg of carbon.

Percentage of carbon in a CO₂ molecule,

  $\begin{array}{l}{\text{Molar mass of CO}}_{\text{2}}{\text{ = 12+32 gmol}}^{\text{-1}}\\ \frac{12}{12+32}\times 100\%\text{=27}\text{.3\%}\end{array}$

  ${\text{Cycled amount of carbon annually in CO}}_{\text{2}}\text{ = 3}\times {\text{10}}^{\text{14}}\text{ kg}\times \frac{27.3}{100}=8.18\times {10}^{13}\text{kg}$

Number of humans could be produced from this amount of carbon,

  $\text{=}\frac{8.18\times {10}^{13}\text{kg}}{12.6\text{ kg}}=6.5\times {10}^{12}$

  $6.5\times {10}^{12}$ humans can be produced from the cycled CO₂ annually.