Lecture Notes: Origin of Atoms and Conservation of Mass

Introduction to Atoms

• Atoms are the fundamental building blocks of all things.
• Key question: Where do atoms come from?

Law of Conservation of Mass

• States that in an isolated system, mass (matter and energy) cannot be created or destroyed.
• The universe is considered an isolated system.

Example of Conservation in Small Systems

• Example: Six carbon, 12 hydrogen, and 18 oxygen atoms.
  • Can form molecules like water and carbon dioxide.
  • Energy facilitates bonding and reshuffling to form substances like simple sugars and oxygen gas.
  • Atoms remain constant: 6 carbon, 12 hydrogen, and 18 oxygen.

Energy in Chemical Reactions

• Energy is stored in chemical bonds.
• Releasing energy involves breaking these bonds, e.g., in sugar back to water and carbon dioxide.

Combustion Reactions

• Methane Combustion
  • Methane + Oxygen + Energy → Carbon Dioxide + Water + Energy
  • Conserves hydrogen atoms throughout reaction.
• Propane Combustion
  • Propane + Oxygen + Energy → More Water and Carbon Dioxide
  • Three CO2 molecules because propane has three carbon atoms.

Law of Conservation of Mass in Reactions

• Mass and energy are conserved in chemical reactions.

Origin of Atoms

• Tracing back to the Big Bang as the origin of hydrogen.
• Star Formation and Nuclear Reactions
  • Stars form clusters of atoms.
  • Nuclear reactions in stars fuse light elements to create heavier elements like carbon and oxygen.
  • Energy released corresponds to a slight loss in mass, explained by Einstein's E=mc².

Supernova and Formation of Earth

• Stars go supernova, scattering elements across space.
• These elements eventually formed Earth and contributed to the formation of life.

Conclusion

• Atoms in all matter, including living organisms, originated from star materials.
• Carl Sagan's famous quote: "We are all made of star stuff."