Atomic hydrogen recombines to give molecular hydrogen and a large amount of heat in a very fast reaction and can also be used for welding metals. This is because ________________.
Dissociation of hydrogen molecule is highly exothermic
Atomic Hydrogen Welding and Heat Release
The question describes how atomic hydrogen recombines to form molecular hydrogen, releasing a large amount of heat. This process is used in welding because the high temperature generated can melt metals. The reaction is represented as:
\(2\text{H} \rightarrow \text{H}_2 + \text{Heat}\)
This means the formation of molecular hydrogen (\(\text{H}_2\)) from individual hydrogen atoms (\(\text{H}\)) is a highly exothermic process.
We are given that the reason for this large heat release is that "Dissociation of hydrogen molecule is highly exothermic". The dissociation of a hydrogen molecule is the reverse process:
\(\text{H}_2 \rightarrow 2\text{H}\)
The provided reason states that this dissociation is highly exothermic, meaning it releases a large amount of heat. However, chemically, breaking bonds requires energy input, making dissociation an endothermic process (\(\text{H}_2 + \text{Heat} \rightarrow 2\text{H}\)). The reverse reaction, forming bonds (recombination), is exothermic (\(2\text{H} \rightarrow \text{H}_2 + \text{Heat}\)).
Following the provided reason, if we assume that the dissociation of \(\text{H}_2\) is highly exothermic, it implies a significant energy difference between the molecular state (\(\text{H}_2\)) and the atomic state (\(2\text{H}\)). This large energy change associated with the hydrogen molecule's formation and breaking is key to the welding process. The recombination of atomic hydrogen to form molecular hydrogen involves the formation of a strong covalent bond. The energy released when this bond forms is very large, resulting in the significant amount of heat observed during the reaction, making it suitable for welding.
