Assertion : All combination reactions are opposite of decomposition
reactions
Reason: CaO + H20-Ca(OH)2 is example showing only combination
reaction :
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
Answers
Answer:
A is correct answer
Explanation:
A great many common reactions are exothermic. The formation of compounds from the constituent elements is almost always exothermic. Formation of water from molecular hydrogen and oxygen and the formation of a metal oxide such as calcium oxide (CaO) from calcium metal and oxygen gas are examples. Among widely recognizable exothermic reactions is the combustion of fuels (such as the reaction of methane with oxygen mentioned previously).
The formation of slaked lime (calcium hydroxide, Ca(OH)2) when water is added to lime (CaO) is exothermic.
CaO(s) + H2O (l) → Ca(OH)2(s)
This reaction occurs when water is added to dry portland cement to make concrete, and heat evolution of energy as heat is evident because the mixture becomes warm.