8.2 Endothermic Reaction

• • a chemical reaction that absorbs thermal energy from the surroundings and change it to chemical energy store in chemical bonds
  • ex: making bread (absorb heat than expand), photosynthesis (absorbs sunlight), dissolving
• Dissolving

  • no chemical reaction has taken place as no new products are formed, the solute just dissolved
  • this is a process
  • solute will absorb thermal energy from the solvent in order for it to break apart to form the solution
• Melting

  • thermal energy is absorbed as the solid ice changes to liquid water
  • as the particles absorb thermal energy, they vibrate more and more
  • when particles have enough energy, they can overcome the forces holding them in place
  • the particles can now slide past one another
  • water is now in a liquid state
• Applications

  Using endothermic reaction

  • ice pack is made from substance that undergo and endothermic process when mixed together
  • when 2 compartments (usually ammonium nitrate and water) are broken the chemical substance starts to dissolve, endothermic processes happens
  • some ice packs are reusable and they are stored in a freezer until they are needed
  • when it's placed in an injured area, heat from the area is transferred from the ice pack and the ice melts (endothermic PROCESS)
  • after it has been used, the ice pack can go back into the freezer to be used again