How can you tell whether a chemical reaction has occured?

Question

How can you tell whether a chemical reaction has occured?

Answer 1

chemical reaction is the one in which reactants react 2 form a new product which is totally different from the constituents

it doesn't show the properties of its constituents

then u cn say that a chemical reaction hs occured

Answer 2

A reaction occurs because there is a product there that wasn't a reactant.  When something new has been produced, then there is a chemical reaction.  If you end up with the same things you started with, then there was no reaction.

A common situation is with double replacement reactions.

KCl + HNO3 --> NO REACTION

suppose you said

KCl + HNO3 --> KNO3 + HCl

but look at the ionic equation

K+ + Cl- + H+ + NO3-  -->  K+ + NO3- + H+ + Cl-

All of these compounds are soluble in water.  The produced the same four ions, so nothing has changed.  Therefore, no reaction.

Consider this

KCl + AgNO3 --> AgCl(s) + KNO3(aq)

Here a reaction occurs because you form an insoluble precipitate that obviously wasn't there to start with.

Answer 3

When a  chemical reaction takes place,chemical change takes place