Percentage change in mass of the reactants when carbon burns in oxygen

Percentage change in mass of the reactants when carbon burns completely in oxygen to CO

Marzo 21st, 2021 | by Marcello Colozzo |

carbon,oxigen,exothermic reaction — **Immagine tratta da questo sito web**

Appunti ed esercizi di Fisica del Reattore nucleare elaborati dell'ing. Giorgio Bertucelli.

Calculate the percentage change in mass of the reactants when carbon burns completely in oxygen to CO₂ . The eating value of C is 141000 Btu/lb_m=32794kJ /kg .

Solution
The chemical reaction

is exothermic reaction. It should be pointed out here that chemical reactions, like nuclear reactions, are either exothermic or endothermic. That is, they either release or absorb energy. Since energy and mass are convertible according to Einstein's law

chemical reactions do undergo changes in mass, (a mass decrease in exothermic reactions, mass increase in endothermic ones), just as nuclear reactions do. However the quantities of energy resulting from chemical reactions are small compared with those in nuclear reactions, and the fraction of mass of the reactants either lost or gained is extremely small. This is why we assume a preservation of mass in chemical reactions.