H₂ reduction potential is ______.

H₂ reduction potential is ______.

• A. 1.23 V
• B. 0.00 V
• C. -0.76 V
• D. 0.50 V

Answer: (B)

In electrochemistry, the standard hydrogen electrode serves as the reference point with a defined reduction potential of zero. Under standard conditions (1 M H+, 1 atm H2, 25°C), the hydrogen couple H+ + e− ⇌ 1/2 H2 is assigned E° = 0.00 V. This convention means hydrogen’s tendency to gain electrons is the baseline for measuring all other reduction potentials, so H2’s reduction potential is zero by definition. Other numbers correspond to different redox couples (for example, the O2/H2O couple is much more positive, around +1.23 V, and some metal couples are negative). If conditions differ from standard states, the actual potential would shift per the Nernst equation, but the standard value remains zero.

In electrochemistry, the standard hydrogen electrode serves as the reference point with a defined reduction potential of zero. Under standard conditions (1 M H+, 1 atm H2, 25°C), the hydrogen couple H+ + e− ⇌ 1/2 H2 is assigned E° = 0.00 V. This convention means hydrogen’s tendency to gain electrons is the baseline for measuring all other reduction potentials, so H2’s reduction potential is zero by definition. Other numbers correspond to different redox couples (for example, the O2/H2O couple is much more positive, around +1.23 V, and some metal couples are negative). If conditions differ from standard states, the actual potential would shift per the Nernst equation, but the standard value remains zero.