How do we know a chemical reaction has taken place?

How the chemical reaction takes place?

Difine a chemical reaction. Which observations help you to determine whether a chemical reaction has taken place ?

Define a chemical reaction. Which observation help you to determine whether a chemical reaction has taken place ?

Which of the following observations DOES NOT help in determining whether a chemical reaction has taken place?

Do you think that a chemical reaction has taken place in the flask ? Give reason.

Do you think that a chemical reaction has taken place in the flask? Give reasons. Do the weights of the flask and its contents change during activity?