# Chemistry - DrBob222

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When sodium burns in air it produces a bright white light and heat energy

2Na + O2 2Na2O ?H = -414kJ/mol

What would you expect to be the heat energy associated with the reverse process

2Na2O 2Na + O2

This is what I have but it is wrong:
2 moles Na2O x +414 kJ/mol /2moles Na2O = +828 kJ

• Chemistry - DrBob222 -

If it is -414 kJ/mol going in the forward direction it must be +414 kJ/mol going in the opposite direction.

the enthalpy -414kJ/mol is the enthalpy of combustion. i.e. how much energy released for one mole of Na metal to burn in air. so the actual equation is;

Na + 1/2O2 --> NaO ?H = -414kJ/mol.

However, the equation given in your question is written in whole number coefficients just to get rid of the 1/2 but keep in mind that the ?H still remain the same in this case.

so simply reverse the sign

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