Question

Setting of cement is:
(A) exothermic reaction
(B) endothermic reaction
(C) neither endothermic nor exothermic
(D) none of these.

Answer 1

Setting is called as the action of changing from a fluid state to a solid state. During setting when water reacts with cement it liberates heat.

Complete step by step answer:
Cement is known to a binder that is used in construction sites.
Depending upon the ability of the cement to set in the presence of water, cement is divided into:
(1). Non-hydraulic cement
(2). Hydraulic cement
Non – hydraulic cement is that which does not set in wet conditions or under water. It sets as it dries and reacts with carbon dioxide in the air. It does not get attacked by the chemicals after setting.
Hydraulic cement is that which sets and becomes adhesive due to a reaction with dry ingredients and water. Hydraulic cements consist of a mixture of silicates and oxides. The process of formation of cement includes the calcination process of limestone that is calcium carbonate. The reaction of burning of limestone is:
${\text{CaC}}{{\text{O}}_{\text{3}}} \to {\text{CaO + C}}{{\text{O}}_{\text{2}}}$
From this reaction carbon is removed from limestone and the formation of lime occurs. Then, after this lime reacts with silicon dioxide to produce dicalcium silicate and tricalcium silicate. The reaction can be written as:
${\text{2CaO + Si}}{{\text{O}}_{\text{2}}} \to {\text{2CaO}}{\text{.Si}}{{\text{O}}_{\text{2}}} \\\ {\text{3CaO + Si}}{{\text{O}}_{\text{2}}} \to {\text{3CaO}}{\text{.Si}}{{\text{O}}_{\text{2}}} \\\$
Then, lime reacts with aluminium oxide to form tricalcium aluminate.
${\text{3CaO + A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}} \to {\text{3CaO}}{\text{.A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}$
At last, calcium oxide, aluminium oxide and ferric oxide react together to form cement.
${\text{4CaO + A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}{\text{ + F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}} \to {\text{4CaO}}{\text{.A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}{\text{.F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}$
When cement is mixed with water it starts to set and causes hydration chemical reactions. The hydration of the constituents occurs slowly and the material solidly and hardens.
$CaO.A{l_2}{O_3} + 6{H_2}O \to 3CaO.A{l_2}{O_3}.6{H_2}O + \operatorname{Heat}$
During setting and hardening of cement, some amount of heat is liberated due to hydration and the chemical reactions that occur.
As the release of heat takes place. So, the setting up of cement is an exothermic reaction.

So, the correct answer is Option A.

Note: Wet cement is strongly corrosive and can cause severe skin burns and even if they come in contact with mucous membranes it can cause severe eye or respiratory irritation.