Using the principles of bond breaking and bond making, how can I explain why there is no change in temperature in phase changes?
In a phase change, for example when boiling water is converted to steam, no O-H bonds are broken and none are made. Enough energy must be added to the liquid water to allow the kinetic energy of the molecules to overcome the intermolecular forces (H bonding, if you will) but that is all that happens, basically. I hope I have understood the question.
Yes, you understood the question, thank you!
You're welcome! So, to explain why there is no change in temperature during phase changes, we need to examine the principles of bond breaking and bond making.
During a phase change, such as the conversion of liquid water to steam, the temperature remains constant because the energy being added or removed is primarily used to overcome the intermolecular forces, rather than to increase or decrease the kinetic energy of the molecules.
In the case of water boiling, the energy being added in the form of heat allows the water molecules to overcome the attractive forces between them, known as hydrogen bonding. This allows the molecules to transition from the liquid phase to the gaseous phase, forming steam. However, the energy added does not significantly increase the average kinetic energy of the molecules, which is directly related to temperature.
When a substance undergoes a phase change, the energy is used to break the intermolecular bonds or forces present in the substance, rather than to break or form intramolecular bonds. In the case of water boiling, the O-H bonds within the water molecules remain intact during the phase change. The energy being supplied is used to weaken the intermolecular hydrogen bonds, allowing the water molecules to move more freely and eventually become a gas.
Once the intermolecular forces are overcome, further energy addition results in an increase in temperature. In the case of water, this occurs when the steam is heated beyond its boiling temperature.
To summarize, during a phase change, the energy is primarily used to overcome intermolecular forces and break the bonds between particles rather than to increase the temperature by increasing the kinetic energy of the particles. This is why there is no change in temperature during the phase change itself.