Question

which is the most important question for deciding if a chemical reaction has occurred?
was there a change in the size?
was any heat energy given off?
what is the density of the substance?
what is the texture of the substance?

Explanation:

Un cambio en el tamaño, textura o densidad son cambios físicos. La emisión de calor es un indicador de una reacción química, ya que implica una transformación en la estructura molecular de las sustancias involucradas.

Answer:

Was any heat energy given off?