Forming a chemical bond releases energy and therefore is an exothermic process. Exothermic reactions usually feel hot because it is giving heat to you. Endothermic-a process or reaction that absorbs energy in the form of heat. Breaking a chemical bond requires energy and therefore is Endothermic.
karma level 71199. The Seikan Tunnel is a 53.85 km (33.46 mi) railway tunnel in Japan, with a 23.3-kilometre (14.5 mi) long portion under the seabed. Track level is about 140-metre (460 ft) below seabed and 240-metre (790 ft) below sea level. It is the longest undersea tunnel in the world, although the Channel Tunnel between the United Kingdom and France has a longer under-sea portion.
Guadarrama is the longest twin-tube rail tunnel in Spain and fourth longest in the world. The 28.4km tunnel is dug through Sierra de Guadarrama mountain range for the high speed railway between Madrid and Valladolid. The two parallel tunnels are 30m apart, measured from their central axes.