Answer:

Explanation:
Hello there!
In this case, according to the given information, it turns out possible to set up the initial version of the half-reaction as follows:

Now, we assign the oxidation numbers to both nitrogen atoms:

It means three electrons are carried, two water molecules are needed on the left side in order to balance the oxygen atoms and consequently four hydronium ions to balance hydrogen atoms in acidic media:

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I think energy is released
Answer:

Explanation:
Hello there!
In this case, according to the given question about stoichiometry, it is possible for us to calculate the required moles of water that will be produced by 12 grams of hydrogen, by using the molar mass of this reactant (2.02 g/mol as it is diatomic) and the 2:2 mole ratio in the chemical equation by solving the following setup:

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