How do you calculate standard molar enthalpy of formation?

For most chemistry problems involving ΔHof , you need the following equation:

ΔHoreaction=ΣΔHof(p)−ΣΔHof(r) ,

where p = products and r = reactants.

i look it up online and i'll tell you

it is to be noted that an alpha particle is an helium nucleus. so it contains 2 protons 2 neutrons and has a mass number of 4. when alpha decay particles are ejected from the nucleus it gets transformed into an atom which has atomic number less than 2 and a mass number less than 4.

an equation that could represent alpha decay is radium 226 decay of alpha particle forms radon 222.

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