Question

What are the characteristics of a chemical reaction?
[A] Evolution of a gas
[B] Formation of a precipitate
[C] Change in color
[D] Change in temperature
[E] All of these

Answer 1

Hint: Generally you should know that chemical reactions occur when two or more molecules interact with each other and undergo certain changes. Chemical reaction causes changes in chemical properties of the substance.

Complete step by step answer:
In simple words we can say that a chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. Basically, it is a process in which one or more substances are converted to one or more different substances.
To answer this question let us see follow the options and check whether or not they are characteristic to a chemical reaction:
- Evolution of gas: There are numerous chemical reactions which are characterized by the evolution of gas.
Example: when sodium carbonate reacts with dilute hydrochloric acid evolution of carbon dioxide takes place.
     $$N{a}_{2}C{O}_3+2HCl(aq)\to 2NaCl(aq)+H_{2}O(l)+C{O}_2(g)$$

Formation of precipitate: There are many chemical reactions which are characterized by the formation of precipitate.
Example: Reaction between silver nitrate and sodium chloride forms a white precipitate of silver chloride.
     $$AgN{O}_3+NaCl\to NaN{O}_3+AgCl\downarrow$$

Change in color: In chemistry we often perform titrations. It is basically a chemical reaction between acids and bases. Its end point is observed by a color change. Besides titrations, there are also many chemical reactions (like formation of metal oxides) which are characterized by a color change.
Example: When citric acid reacts with potassium permanganate, the purple color of potassium permanganate disappears.
     $$C_6{H}_8{O}_7+3KMn{O}_4\to 3HMn{O}_4+C_6{H}_5{K}_3{O}_7$$

Change in temperature: There are certain chemical reactions that are characterized by change in temperature. The reactions in which heat is evolved are called exothermic reactions and the reactions in which heat is absorbed are called endothermic reactions.
Example: When quick lime reacts with water then slaked lime is formed and energy is produced. This is an exothermic reaction.
     $$CaO+H_{2}O\to Ca{\left(OH\right)}_2$$

We can see from the above discussion that all of these are a characteristic of a chemical reaction.
So, the correct answer is “Option E”.

Note: You should know that mixtures and solutions are quite different from chemical reactions as we already know the molecules of the substance remain the same.
Chemical reactions play an important role in technology, culture and indeed life itself. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans.