Question

What is the only way to be certain that a chemical change has occurred

Answer 1

The best way to determine whether a change is physical or chemical is to determine if the substance identity has changed or not. All chemical changes involve a transfer of energy. The only way to be certain that a chemical reaction has taken place is to test the composition of the substances after the change has taken place, to see if they are different from the starting substances.

Step-by-step explanation:

The best way to determine whether a change is physical or chemical is to determine if the substance identity has changed or not.

All chemical changes involve a transfer of energy. When zinc reacts with hydrochloric acid, the test tube becomes very warm as energy is released during the reaction. Some other reactions absorb energy. While energy changes are a potential sign of a chemical reaction, care must be taken to ensure that a chemical reaction is indeed taking place. Physical changes also involve a transfer of energy. The melting of a solid absorbs energy, while the condensation of a gas releases energy. The only way to be certain that a chemical reaction has taken place is to test the composition of the substances after the change has taken place, to see if they are different from the starting substances.

Answer 2

New kinds of products forms and the reaction is not easily reversible.

Step-by-step explanation:

The only way to be certain that a chemical change has occurred is by finding out if new kinds of products have been formed.

A chemical change is a change in which new kinds of matter is formed. It is always accompanied by energy changes.

The process is not easily reversible.

Examples of chemical changes are combustion, rusting of iron, precipitation and souring of milk.