Evidence of chemical reactions Original Scenario-Based Practice

Questions

1. 1.

   A deep-space botanist aboard an exploratory vessel combines two clear, room-temperature solutions in an unheated glass flask to synthesize an artificial plant nutrient. Within seconds, a dense, bright-yellow solid forms and settles at the bottom while the flask becomes noticeably warm to the touch without any boiling. Which statement best explains why these observations provide conclusive evidence that a chemical reaction occurred?

   • A) The change is purely physical because the two transparent liquids merely separated back into their original constituent components.
   • B) The release of thermal energy confirms a simple phase change, while the yellow powder is an unchanged solute left behind by rapid evaporation.
   • C) The spontaneous formation of an insoluble solid precipitate and the exothermic temperature change demonstrate that new chemical substances were produced.
   • D) The process represents a reversible mechanical mixture where the physical dissolution of ions temporarily shifted the color of the liquid.

Answers and step-by-step solutions appear after you finish the test.