Question

Write the chemical equation of the reaction in which the following changes have taken place with an example of each.
i) Change in colour
ii) Change in temperature
iii) formation of precipitate

Answer 1

Hint: In chemistry, equations play a major role. In the reaction three things are main. There are reactant, product and reaction conditions. The reactants are always on the left side of the equation. If more than one reactant in the equation means by using plus sign. The products are always on the right side of the reaction. Something here also follows. More than one product by using plus sign. In between reactant products are used arrows to find the reaction direction in the equation.

Complete answer:
The chemical equation of the reaction in the following changes have taken place with an condition is given below,
i) Change in colour
\[{\text{Pb(N}}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}{\text{ + 2KI}} \to {\text{Pb}}{{\text{I}}_{\text{2}}}{\text{ + 2KN}}{{\text{O}}_{\text{3}}}\]
Lead nitrate reacts with potassium iodide to give lead iodide as a product. The reaction mass changes colour from colourless to yellow colour spangles due to lead iodide.
ii) Change in temperature
Zinc is reacted with sulphuric acid to give zinc sulphate as product and evolution of hydrogen. The evolution of hydrogen gives energy from heat, and temperature will increase.
 \[{\text{Zn + }}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}} \to {\text{ZnS}}{{\text{O}}_{\text{4}}}{\text{ + }}{{\text{H}}_{\text{2}}}\]
iii) Formation of precipitate
\[{\text{NaOH + }}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}} \to {\text{N}}{{\text{a}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}}\]
Sodium hydroxide is reacted with sulphuric acid to give sodium sulphate as a precipitated product in water.

Note:
In balanced chemical reaction wise, we predict the side product of the reaction. In some cases we are not able to attain the balance by changing the mole. In that case we use the number of countable ions in the product and reactant side of the chemical reaction. In chemistry, redox reaction is one of the types of major reactions. In this redox reaction two methods are used to attain the balanced chemical reaction. There are ion-electron methods and the oxidation number method.