GED Science TestPhysical ScienceMedium
A chemist is performing an experiment where they mix two clear, colorless solutions. After mixing, the solution remains clear, but the test tube feels noticeably colder to the touch. What does this observation primarily indicate?
- AA physical change has occurred, and the solution is now denser.
- BAn endothermic reaction has occurred, absorbing heat from the surroundings.
- CThe solutions have combined to form a precipitate, indicating a new substance.
- DAn exothermic reaction has occurred, releasing heat into the surroundings.
Show answer & explanationAnswer & explanation
Correct answer: B. An endothermic reaction has occurred, absorbing heat from the surroundings.
If the test tube feels colder, it means the reaction has absorbed heat from its surroundings, which is the definition of an endothermic reaction. A physical change typically doesn't involve a significant temperature change unless external factors are applied. An exothermic reaction would release heat, making the test tube warmer. The absence of cloudiness means no precipitate formed.
Why the other options are wrong
- A. Temperature change is a strong indicator of a chemical reaction, not just a physical change; density isn't directly indicated.
- C. The solution remained clear, indicating no precipitate formed.
- D. An exothermic reaction releases heat, making the surroundings warmer, not colder.
Endothermic Reaction
An endothermic reaction is a chemical reaction that absorbs energy from its surroundings, usually in the form of heat, resulting in a decrease in the temperature of the surroundings.
- Absorbs heat from surroundings
- Temperature of surroundings decreases (feels cold)
- Requires continuous energy input to proceed
Memory trick: Endo = Enter heat, Exo = Exit heat