Explain how each of these helps in bringing about a chemical change.

Light.

Fill in the blanks with the correct answers in the following statement:

Dissolving common salt in water is an example of a _____ change.

Dissolving zinc in dilute ${\mathrm{H}}_2{\mathrm{SO}}_4$ is an example of a _____ change. (natural / chemical)

Fill in the blanks with the correct answer in the following statement:

A _____ change is one in which one or more different substances are formed.

Fill in the blanks with the correct answer in the following statement:

A _____ can easily be reversed.

Fill in the blanks with the correct answer in the following statement:

Every substance has a fixed amount of _____ energy. (potential / kinetic)

Which one of the following substances does not undergo a chemical change on heating:

A small piece of sodium is dropped into a beaker of water. Give two reasons why this reaction involves a chemical change.

What is meant by the term catalyst?