Which of the following is not a chemical change? (A) Sublimation (B) Combustion (C) Electrolysis (D) Rusting
Hint: To solve this problem firstly we should know what chemical change is and the process and type reactions involved. We will first study these terms one by one and the process involved, and then it would be easy for us to reach our conclusion for this question.
Complete step by step solution: > A chemical change happens when one chemical substance is transformed into one or more different substances. Chemical change occurs through the process of chemical reactions, and the resulting substances have different properties because their atoms and molecules are arranged differently. > Sublimation is a process in which the substance’s phase transition occurs directly from solid to the gaseous phase. Hence, it is physical change not chemical. > Combustion is defined as the reaction of the compound with oxygen, which is a chemical reaction, hence the chemical change. When fuel reacts with the oxygen, it releases the heat and light energy. Heat and light energy produce the flame. Hence, this is a chemical change. > Electrolysis is the chemical process of decomposition of a substance through passing electric current. The chemical change can also be defined as the one in which the substance loses or gains an electron. Hence this is also a chemical change. > Rusting is a process involving the reaction of metals with moisture (air+ water). Thus, it is a chemical change. Rusting is the formation of rust, a mixture of iron oxides, on the surface of iron objects. The rust is formed from the redox reaction between oxygen and iron in the environment. Hence, the correct answer is option A. Sublimation.
Note: Sublimation, in simple words, is a process in which a solid converts into a gaseous phase directly, without first melting to form a liquid phase. Frequently takes place with substances having a high vapor pressure at room temperature. Sublimation is occasionally used in the laboratory as a method of purification of solids. Eg: caffeine.