Hydrogen and oxygen react under a specificset of conditions to produce water accordingto the equation2 H2(g) + O2(g) −→ 2 H2O(g).How much hydrogen would be required toproduce 3.9 mol of water?Answer in units of mol.

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1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

Answerthe half-reaction having the greatest tendency to occur at the anode:     i₂(aq) + 2e⁻  ⇄ 2i⁻  ;   e = +0.53 v======oxidation occurs at the anode. we must therefore find the half-reaction with the greatest tendency to oxidize.the given values of e are reduction potentials (the form of the half-reactions are of reduction).the lower the reduction potential, the higher the potential to oxidize. the half-cell with the lowest reduction potential will have the greatest tendency to oxidize at the anode.the half-reaction having the greatest tendency must be    i₂(aq) + 2e⁻  ⇄ 2i⁻    e = +0.53 vbecause its reduction potential is the lowest out of the three.