Hydrogen and Its Properties

Hydrogen Properties

  • Most Simple Element: Hydrogen consists of one proton and one electron.
  • Abundance: Most abundant element in the universe; third most abundant on Earth (exists as water and hydrocarbons).
  • Gaseous State: Small percentage exists as $ ext{H}_2$ gas in the atmosphere (0.6 ppm).
  • Gravity Effects: Earth's gravity insufficient to retain lighter elements like hydrogen.
  • Elementary Hydrogen: Dihydrogen $ ext{H}_2$.
  • Hydrogen Economy: Increasing focus on hydrogen energy.

Hydrogen as Energy Source

Advantages:
  • Renewable Production: Can be produced from renewable sources.
  • Clean Combustion: Combustion only produces $ ext{H}_2 ext{O$ (water).
Disadvantages:
  • Storage and Transport: Challenges in inconvenience.
  • Low Density per Volume: Energy density is 8 MJ/L (liquid $ ext{H}_2$) versus 30 MJ/L for petrol.
  • High Energy Density per Mass: 120 MJ/kg compared to 50 MJ/kg for crude oil and <1 MJ/kg for lithium batteries.

Hydrogen Production Methods

  • Global Production: Approximately 100 million tons annually.
  • Fossil Fuel Dependency: Majority produced via fossil fuels (only 1% considered green).
  • Electrolysis Contribution: Less than 0.1% produced by electrolysis of water.
  • Steam Reforming: Around 60% produced by steam reforming of hydrocarbons.
  • Coal Gasification: About 20% via gasification of coal.

Key Reactions for Hydrogen Production

  1. Steam Reforming:

    • Reaction: $ ext{CH}4 + ext{H}2 ext{O}
      ightarrow ext{CO} + 3 ext{H}_2$
    • Conditions: Nickel catalyst, 800-1000 °C, 20-30 bar (endothermic, $ ext{ΔH} = 204 ext{ kJ/mol}$).

  2. Water-Gas Shift Reaction:

    • Reaction: $ ext{CO} + ext{H}2 ext{O} ightarrow ext{CO}2 + ext{H}_2$
    • Conditions: Iron oxide catalyst, 400 °C (exothermic, $ ext{ΔH} = -42 ext{ kJ/mol}$).

  3. Coal Gasification:

    • Processes include various endothermic and exothermic reactions producing hydrogen and carbon monoxide.

Physical and Chemical Properties of Hydrogen

  • Properties: Colorless, non-toxic, odorless gas.
  • Melting Point: 14 K = -259 °C.
  • Boiling Point: 20 K = -253 °C.
  • Hydrogen Liquefaction: Does not liquefy under pressure; liquid hydrogen stored at 350 bar or at low temperature.

Hydrogen Bonds

  • Definition: An attraction between hydrogen attached to an electronegative atom and another atom with lone pairs.
  • Role in Water: Hydrogen bonds result in unusual properties of water, such as higher boiling points and lower densities of ice compared to liquid water.

Isotopes of Hydrogen

  • Hydrogen Isotopes:
    • Protium ($^{1} ext{H}$ or H): 99.985% abundance.
    • Deuterium ($^{2} ext{H}$ or D): 0.0156% abundance.
    • Tritium ($^{3} ext{H}$ or T): <10^-15% and radioactive.
  • Applications:
    • Deuterium in nuclear reactors, spectroscopy.
    • Tritium primarily in nuclear weapons.