# Effect of redefining Avogadro's constant and kilogram on molar mass

Avogadro's constant $$N_\mathrm A$$ is defined as the number of constituent particles (usually atoms or molecules) contained in the amount of substance given by one mole.

The value of Avogadro's constant $$N_\mathrm A$$ is going to be set to exactly $$6.02214076\times 10^{23}\ \mathrm{mol}^{-1}$$ in 2019.

I might add that the kilogram is also going to be redefined in 2019 based on Planck's constant.

Will these changes result in the molar mass of a substance no longer being exactly equal to the molecular mass expressed in grams?

• Nov 17 '18 at 20:33
• Atomic weights will no longer be based on carbon 12. But unless you're experimenting to 1 part per billion or better you won't notice the difference.
– MaxW
Nov 17 '18 at 21:01