A student pours two chemicals into a beaker.
Which activity provides the best evidence that a chemical reaction is happening?
A. wafting above the beaker to check for smells
B. looking for a phase change in one or both chemicals
C. measuring the temperature of the liquid to see if it is changing
D. swirling the contents of the beaker to see if the two chemicals separate
The best answer is C. measuring the temperature of the liquid to see if it is changing.
A change in temperature often indicates that a chemical reaction is taking place, as exothermic reactions release heat and endothermic reactions absorb heat. While phase changes and odors can also suggest a reaction, measuring temperature provides direct evidence of energy changes occurring during the reaction.