Which one of the following is not an endothermic reaction?

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Combustion of methane

Decomposition of water

Conversion of graphite to diamond

Dehydrogenation of ethane

answer is B.

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Detailed Solution

Concept- Chemical processes referred to as endothermic reactions occur when the reactants take in heat energy from their environment to create products. These reactions have a cooling effect by bringing the temperature of the space around them down. An example of an endothermic physical process is the melting of ice cubes, which absorb heat energy from their environment (no chemical bonds are broken or formed).
In an endothermic reaction, heat is evolved
1) The process of combustion is always exothermic.
2) Water needs energy to break down. Therefore, it is endothermic.
3) Dehydrogenation, which produces ethylene from ethane, is an endothermic reaction because it requires energy to split the bonds.
4) Diamond cannot be created from graphite since doing so would demand energy. The excess energy required is finally stored in the tetrahedral structure of the diamond.
Hence, choices 2, 3, and 4 are the proper responses.

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