Which of the following is an exothermic reaction ?

ANS:D - none of these

1. Conversion of graphite to diamond:
   • This process involves transforming graphite, which consists of layers of carbon atoms arranged in a hexagonal lattice, into diamond, where carbon atoms are arranged in a three-dimensional tetrahedral lattice.
   • Converting graphite to diamond requires breaking and rearranging chemical bonds in the carbon atoms. This restructuring requires energy input rather than releasing energy, so it's an endothermic process.
   • Therefore, this reaction is endothermic.
2. Decomposition of water:
   • Water molecules (𝐻2𝑂H2​O) can be decomposed into hydrogen gas (𝐻2H2​) and oxygen gas (𝑂2O2​) through a process known as electrolysis.
   • Electrolysis of water involves passing an electric current through water, causing it to dissociate into hydrogen and oxygen gases.
   • Breaking the bonds in water molecules requires energy input to overcome the bond energies, making this reaction endothermic.
   • Therefore, this reaction is endothermic.
3. Dehydrogenation of ethane to ethylene:
   • Dehydrogenation is the removal of hydrogen atoms from a molecule.
   • In the dehydrogenation of ethane (𝐶2𝐻6C2​H6​) to ethylene (𝐶2𝐻4C2​H4​), a molecule of ethane loses two hydrogen atoms to form a molecule of ethylene.
   • Breaking the C-H bonds in ethane releases energy, and the formation of C=C double bond in ethylene releases even more energy. Overall, this process releases energy in the form of heat.
   • Therefore, this reaction is exothermic.