are covalent bonds broken when....
melt benzene
melt quartz
boiling C2H5OH
evaporating water
disolving bromine in water?
You really need to define what you mean by covalent bond in order for us to answer this question. For example, hydrogen bonds are broken when C2H5OH is boiled but H bonds are only about 1/20 as strong as a regular covalent bond. Same thing for crystal structure. Are the bonds in the crystal structure of solid benzene covalent bonds by your definition.
Covalent bonds are formed when electrons are shared between atoms. In order to break these bonds, energy needs to be supplied to overcome the forces holding the atoms together.
Melt benzene:
To melt benzene, which has a covalent bond between carbon and hydrogen atoms, you need to supply enough heat to increase the temperature of the substance above its melting point. As the temperature rises, the kinetic energy of the molecules increases, eventually breaking the intermolecular forces, not the covalent bonds themselves.
Melt quartz:
Quartz is made up of silicon and oxygen atoms bonded by covalent bonds to form a three-dimensional structure known as a network solid. To melt quartz, you would need to supply an extremely high amount of heat, typically above its melting point of around 1670 degrees Celsius, to break the strong covalent bonds within the crystal structure.
Boiling C2H5OH (ethyl alcohol):
Ethyl alcohol, or C2H5OH, is a covalent compound held together by covalent bonds between carbon, hydrogen, and oxygen atoms. To boil ethyl alcohol, you need to increase its temperature to or above its boiling point, which is 78.4 degrees Celsius. At this temperature, the kinetic energy of the molecules overcomes the intermolecular forces, not the covalent bonds themselves, causing the liquid to change into a gaseous state.
Evaporating water:
To evaporate water, which is composed of hydrogen and oxygen atoms bonded through covalent bonds, you need to increase its temperature to or above its boiling point, which is 100 degrees Celsius at standard atmospheric pressure. The heat provides energy to the water molecules, allowing them to move faster and eventually overcome the intermolecular forces that hold them together in the liquid phase. The covalent bonds within individual water molecules are not broken during evaporation.
Dissolving bromine in water:
When you dissolve bromine, which exists as diatomic Br2 molecules, in water, the bromine molecules are surrounded by water molecules due to the attractive forces between polar water molecules and the polar Br2 molecules. In this process, covalent bonds within the bromine molecule are not broken, but instead, new interactions occur between the bromine and water molecules. The bromine molecules mix with the water molecules, resulting in the formation of bromine ions and hydration of the ions.