Evidence of chemical reactions Original Scenario-Based Download PDF

Questions

1. 1.

   During an expedition inside an ancient crystal cavern, a researcher combines two room-temperature, clear, colorless aqueous extracts collected from subterranean mineral pools. Within seconds of mixing without any external heat source, dense canary-yellow flakes settle at the bottom of the flask while the temperature of the container spontaneously rises by 12 °C. Which conclusion is best supported by these observations, and what chemical evidence confirms it?

   • A) A purely physical change occurred, because the observed warming is solely caused by mechanical friction generated while swirling the two liquids together.
   • B) A chemical change occurred, evidenced by the spontaneous formation of an insoluble precipitate and an exothermic temperature change indicating new chemical bonds formed.
   • C) A physical phase change occurred, because the settling yellow flakes represent the liquid solvent rapidly freezing into crystals as thermal energy increases.
   • D) No chemical change took place, because combining two transparent solutions always results in a homogeneous mixture that retains the original chemical identities.