Hydrogen Study Notes

Page 1: Periodic Table Overview

  • Elements are categorized into three main groups: s, p, and transition metals.
  • The periodic table is structured in periods (horizontal rows) and groups (vertical columns).
  • Groups include:
    • s block: Groups 1 and 2
    • p block: Groups 13 to 18
    • d block: Transition metals
    • f block: Lanthanides and Actinides

Page 2: Hydrogen Properties

  • Oxidation states of Hydrogen: 0, -1, +1.
  • Electron configuration: 1s1
  • Melting point (Tm = 14 K), Boiling point (Tb = 20 K).
  • Density of gaseous hydrogen: 0.09 g/L.
  • Covalent bond length (rcov): 32 pm.
  • Ionization energy (Ei): 13.6 eV.
  • Heat of reaction:
    ext{H}_2(g)
    ightarrow 2 ext{H} ext{ with } ext{ΔH} = 436 ext{ kJ/mol}
  • Electrochemical potential:
    E^∘ ext{(H}_2/ ext{H}^-) = -2.23 ext{ V}
  • Comparison with group 1 and 17 elements.

Page 3: Isotopes of Hydrogen

  • Isotopes: ¹H (protium), ²H (deuterium), ³H (tritium).
  • Tritium half-life (t1/2): 12 years.
  • Occurrence of deuterium in water: 1 atom per 1017 hydrogen atoms in water.
  • Production of D₂O (heavy water) via water electrolysis:
    ext{1 m}^3 ext{H}2 ext{O} ightarrow 40 ext{ cm}^3 ext{D}2 ext{O}
  • Concentration
    ext{0.0156\% } -0.0044 ext{ V vs SHE}.

Page 4: Properties of Hydrogen

  • Density in liquid form: 0.07 g/mL.
  • In gaseous form: 0.09 g/L.
  • Historical context: Zeppelin disaster (Hindenburg) in 1937.

Page 5: Reactivity of Hydrogen

  • Standard conditions: T = 25 K and w = 300 K.
  • At 300 K: 0.749 for H2 and 0.251 for H.
  • Affects thermal conductivity.

Page 6: Reactivity of Atomic Hydrogen


  • H2 + Cl2
    ightarrow 2HCl

  • 2H + S
    ightarrow H_2S

  • 2H + CO_2
    ightarrow HCOOH
  • Strongest homonuclear single bond: 74 pm (can occur at lower temperatures).

Page 7: Molecular Hydrogen Reactivity

  • H2 + Cl2 ightarrow 2HCl ext{ and } ΔH< 0

    • H2 + O2
      ightarrow ext{ reactions at } 400°C

  • Ca + H2 ightarrow CaH2 ext{ at } 500 °C

  • N2 + 3H2
    ightarrow 2NH_3
  • Catalytic properties and redox potential.

Page 8: Standard Electrode Potential

  • Standard hydrogen electrode (SHE): P(H2) = 1 bar, T = 298 K.
  • Reaction:
    ext{AH}_2 = 1 ext{ (with HCl)}, A: Pt
  • Standard potential for H+ is zero at this condition: +0.799 V.

Page 9: Redox Reactions and Standard Reduction Potentials


  • Reactions of various oxidants and reductants with their standard potentials:

OxidantReduction ReactionE0 (V)
F2(g)
F2 + 2e^{-} ightarrow 2F^{-} | +2.890 | | Ce4+ | Ce^{4+} + e^{-} ightarrow Ce^{3+} | +1.720 | | Ag+ | Ag^{+} + e^{-} ightarrow Ag(s) | +0.799 | | Fe3+ | Fe^{3+} + e^{-} ightarrow Fe^{2+} | +0.771 | | O2 | O2 + 2H^{+} + 2e^{-}
ightarrow H2O2+0.695
Cu2+
Cu^{2+} + 2e^{-}
ightarrow Cu(s)+0.339
2H+
2H^{+} + 2e^{-}
ightarrow H_2(g)0.000
Zn2+
Zn^{2+} + 2e^{-}
ightarrow Zn(s)-0.762
K+
K^{+} + e^{-}
ightarrow K(s)-2.936
Li+
Li^{+} + e^{-}
ightarrow Li(s)-3.040

Page 10: Laboratory Hydrogen Generation

  • Kipp apparatus used for generating hydrogen.
  • Reaction: Zn + 2H^+
    ightarrow H_2 + Zn^{2+}
  • Metals that yield negative standard potentials produce Hydrogen.

Page 11: Hydrogen Generation Processes

  • Reduction of ions:
    H^+ + e^{-}
    ightarrow rac{1}{2}H_2, Eo = 0 ext{ V}
  • Nernst equation for calculating potentials: E = Eo + 0.059 imes ext{log}(H^+/ ext{mol} ext{dm}^{-3})
    • Special cases with water:
      H2O + e^{-} ightarrow OH^{-} + rac{1}{2}H2, Eo = -0.83 ext{ V}

Page 12: Metal Reactions with Water

  • Sodium and water reaction introduces hydrogen:
    Na + H2O ightarrow Na^+ + OH^{-} + rac{1}{2}H2,
  • Examples of zinc with acidic conditions:
    Zn + 2H^{+}
    ightarrow Zn^{2+} + H_2.
  • Zinc and alkaline solutions lead to different side reactions.

Page 13: Electrolysis Process

  • Reduction at the cathode:

    2H2O + 2e^{-} ightarrow H2 + 2 OH^{-}

  • Other reducing agents leading to Hydrogen involve entrained water and metal reactions.

Page 14: Industrial Hydrogen Production

  • Ethylene glycol cracking:
    C2H6
    ightarrow C2H4 + H_2 ext{ at } 900°C
  • Propane reactions yielding hydrogen.
  • Steam reforming primarily used in industry, with focus on efficiency.

Page 15: Hydrogen Production Ratios

  • Stoichiometric ratios define efficiency of hydrogen producing reactions under specified soaring conditions.

Page 16: Hydrogen Economy

  • Production, storage, and utilization issues (95 % derived from fossils).
  • Risks and opportunities associated with harnessing renewable sources for hydrogen.

Page 17: Energy Density Comparisons

  • Comparative energy densities across fuels; Liquid hydrogen provides significant potential storage but issues of handling and safety remain essential in engineering.