One example of possible evidence of chemical reaction

One example of chemical reaction is when heat is absorbed or released.

For example, when you put a zinc strip into hydrochloric acid, you see bubbles formed and if you touch the test tube, you may feel warmth.

Or for example, if you heat up iron with Sulphur in a correct amount vigorously, you may get a new brown solid.

Therefore, chemical reaction is very likely to take place when heat is released or absorbed.