Answer
a. physical change
b. physical change
c. chemical change
d. physical change
Work Step by Step
a. Sodium chloride is melted. We know that melting is the physical process that utilizes the heat to change the physical state of a solid substance into its liquid form. The process of melting doesn’t change the chemical identity of the substance. Therefore melting of sodium chloride means that sodium chloride is heated so that its physical state is changed from solid to liquid. This process of melting doesn’t change the chemical identity of sodium chloride.
b. Rock salt is pulverized. In this process, rock salt is crushed into smaller pieces of rock salt, that still have the same chemical identity. Therefore this is a physical change as there is a change in the form ( smaller pieces) but the chemical identity is the same.
c. Burning of sulfur. The process of burning requires oxygen, and in this process new substance(s) are formed. As new substances are formed, the change is a chemical change. Burning of sulfur means that oxygen is required in the process, and sulfur is transformed in a new substance, thus this is a chemical change.
d. Dissolving of salt into water is a physical process as no chemical changes happen.
