Question

Please explain how the following two combustion (burning) reactions appear to disobey the law of conservation of Mass: a When a diamond is burned, the mass that remains is zero. B. When a piece of wood is burned, the leftover ashes weight less than the wood. Upon further investigation, it is noted that CO2 is vented off from both reactions. With this additional information, state how you can prove the diamond is made of pure carbon ans yet the wood is not.

Answer 1

Both diamond and wood contain Carbon

C(s) on combustion yields CO2 gas which escapes into the atmosphere.

C(s) + O2(g)= CO2(g)

The masses of one of the reactants (O2(g) and the product CO2 gas are not taken into account during mass calculations

Hence the reactions appear to disobey the law of conservation of mass

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If a material is made up of only Carbon, no residue would be left behind after combustion because the whole of the material would have been converted into CO2 gas which escapes.

On the other hand if a material is made of not only Carbon but also other nonvolatile substances , the nonvolatile substances would remain as residue after combustion.

When a diamond is burned, the mass that remains is zero. So it follows that diamond is made of pure Carbon

Wood on burning leaves behind ashes. So wood is not pure Carbon ; it contains other nonvolatile substances also

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( Diamond is PURE carbon ie made up of only C atoms. So when it is burned in air it is completely converted into CO2 gas which escapes into the atmosphere and no product is left behind Hence the reaction appears to disobey the law of conservation of mass

If collected ,the mass of CO2(g) produced would be found to be equal to the sum of the masses of C(s) and O2(g)

A piece of wood is made up Carbon as well as other noncombustible materials. When wood is burned only the Carbon is converted into CO2 gas and the nonvolatile components remain as a residue. Since the CO2 gas has escaped the reaction appears to disobey the law of conservation of mass.)

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