Chemical reactions of any kind ---> No conversion. All mass (and energy) is conserved.
Nuclear reactions ---> Yes, mass is converted to energy, in both fission and fusion reactions.
Chemical reactions of any kind ---> No conversion. AllWhat mass? Well, going by my college instruction, I would have said that a neutron is lost (andconverted to energy). But a quick surf of the internet shows me that what I learned in college is conservednow considered an old wives' tale. The new answer, though obviously not what I learned, defies my efforts to understand, let alone condense into easy reader format for you. Maybe someone else will give it a go.