Hi I'm a chemist, my current work is with PFAS compounds, often known as forever chemicals. Please ask me about those, or anything else you are curious about related to chemistry. I will try to give you a solid response.

  • ZoomeristLeninist [comrade/them, she/her]M
    ·
    2 years ago

    a lot of factors affect elasticity. for plastics (rubber included) elasticity is mostly conferred due to the molecules configuring in a way that minimizes free energy. when you stretch a rubber band you are stretching the molecule, increasing the free energy of the molecule (rubber bands are actually one big molecule which is why it doesnt melt and will just burn if heated), when you release the rubber band the molecule settles back to its preferred configuration. latex fluid from trees has many free isoprene molecules (which is why it is liquid) but can undergo a reaction to fully polymerize the isoprene to create usable rubber

    in plastics that are more than one molecule elasticity is reduced but has higher plasticity (opposite of elasticity). this is because molecules can more easily separate from each other as they are only affected by weak intermolecular forces rather than strong chemical bonds. applying heat in these plastics increases plasticity/reduces elasticity as there is more energy in the system and the molecules are more "comfortable" being separated from each other

    • join_the_iww [he/him]
      ·
      2 years ago

      rubber bands are actually one big molecule which is why it doesnt melt and will just burn if heated

      I already knew this, but I'm gonna take this opportunity to ask something that's been bothering me about it for a while:

      If a rubber band is one big molecule, then what's going on chemically when a rubber band gets stretched too far & snaps?

      • ZoomeristLeninist [comrade/them, she/her]M
        ·
        2 years ago

        good question.

        when you stretch the rubber band you are increasing the energy of the system. with enough stretching the molecule has enough energy for the chemical bonds to spontaneously cleave. you will still have one molecule but if you break it in two places you get two molecules!

        • ZoomeristLeninist [comrade/them, she/her]M
          ·
          2 years ago

          good question.

          when you stretch the rubber band you are increasing the energy of the system. with enough stretching the molecule has enough energy for the chemical bonds to spontaneously cleave. you will still have one molecule but if you break it in two places you get two molecules!