Do bubbles, heat, formation of a solid always mean a reaction has taken place? Can you think of examples when they do not? What may be happening instead?

A chemical reaction always results in a new substance. A physical reaction only changes the physical properties of the reactants. For example, when you boil a pot of water, bubbles are formed and the water heats up. However, this is not a chemical reaction because the liquid water evaporates and becomes water vapor, a gas. A new substance is never formed.

its mg hope this

all eukaryotic cell have mitochondria : )