A student knows that the sublimation point of carbon dioxide (CO2) is -78.5°C. That is, at this temperature, solid carbon dioxide will change state directly from a solid to a gas. The student is asked to predict the temperature at which gaseous carbon dioxide will change directly from a gas to a solid. Which prediction will be
supported by experimental evidence?

A. The change of state will occur at a temperature greater than -78.5°C.

B. The change of state will occur at a temperature less than -78.5°C.

C. The change of state will occur at a temperature of -78.5°C.

D. The change of state will occur at a temperature of 0°C.

True

Explanation:

A chemical change is otherwise known as a chemical reaction. A chemical change is characterized by the formation of new substances, evolution of heat and change in chemical composition of substances. The change in the composition of substances during a chemical change is the result of the making and breaking of chemical bonds during a chemical change.

A chemical change is not easily reversible because it involves changes in chemical composition of substances.

An example of a chemical change is the combination of sodium hydroxide and hydrochloric acid according to the reaction equation;

HCl(aq) + NaOH (aq) > NaCl(aq) + H2O (l)

We easily notice the change in the chemical composition of each of the substances involved in the reaction.