Question

One of the following is an exothermic reaction. This is:
A. electrolysis of water.
B. conversion of limestone into quicklime.
C. process of respiration.
D. process of photosynthesis.

Answer 1

When energy is released or developed due to any reaction, that reaction is called an exothermic reaction. And if the energy gets absorbed due to any reaction, then it is called an endothermic reaction. At a high-temperature rate of exothermic reaction decreases and the endothermic reaction rate increases. but at low temperatures, the rate of exothermic reaction increases, and the rate of endothermic reaction decreases.

Complete step by step answer:
In the case of electrolysis of water, water gets dissociated into hydrogen ion and hydroxyl ion. This electrolysis is possible under heating, so this reaction absorbs energy, it is an endothermic reaction. The reaction is shown below,
$2{H_2}O\left( l \right) \to 2{H_{2}}\left( g \right) + {O_2}\left( g \right)$
In case of conversion of limestone into quick lime is a heating process. Due to the heating of limestone, it converted into quick lime, so it is not an exothermic reaction. It is an endothermic reaction. The reaction is shown below.
$CaC{O_3}(s)\mathop \to \limits^\Delta CaO(s) + C{O_2}(g)$
In the case of photosynthesis, the sunlight which is light energy gets absorbed and converted into chemical energy. S this is not an exothermic reaction. The reaction is shown below,
$6C{O_{2}} + 6{H_2}O \to {C_6}{H_{12}}{O_6} + 6{O_2}$
But in the case of the respiration process, in presence of oxygen breakdown of the carbon-oxygen bonds of glucose takes place. In this process heat generated. That is the respiration process is an exothermic reaction. The reaction is shown below,
${C_6}{H_{12}}{O_6} + 6{O_2} \to 6C{O_{2}} + 6{H_2}O + energy$

Note: Antoine L Lavoisier is a famous chemist who has contributed a lot to the field of advanced sciences. He was the scientist who experimentally determined that combustion and respiration are caused by chemical reactions. Lavoisier proposed the law of definite proportions, which states that elements combine to form compounds in well-defined proportions, instead of mixing in random proportions.