Effect of temperature on benzenediazonium during diazotization
Diazonium salts are prone to ejection of molecular nitrogen. The process is fairly slow for aromatic diazonium salts, so the salts are usually relatively stable around 0 celsius (alkyldiazonium salsts, though, are a completely different matter). In case of benzenediazonium resulting phenyl-cation is extremely active and will react with first nucleophile present, in many cases it is water, so the product would be phenol.