russ_watters said:How could it be anything but fixed?
So, that question boils down to what is a liquid/what is a gas/why are they different states of matter?mrspeedybob said:I suppose one could ask why phase transition is a discrete transition. The OP asked why phase transition is isothermal. I could re-state that question to ask why does a liquid absorb heat and convert to a gas at the same temperature? Why does the liquid not simply absorb more and more heat, and become less and less dense, and gradually change properties from those of a liquid to those of a gas as it's temperature rises?
Perhaps i could not phrase my question well so i am writing the exact statement of a textbook which is like thismrspeedybob said:I suppose one could ask why phase transition is a discrete transition. The OP asked why phase transition is isothermal. I could re-state that question to ask why does a liquid absorb heat and convert to a gas at the same temperature? Why does the liquid not simply absorb more and more heat, and become less and less dense, and gradually change properties from those of a liquid to those of a gas as it's temperature rises?
The scientific explanation for boiling occurring at a fixed temperature is based on the principles of thermodynamics. When a liquid is heated, the molecules gain kinetic energy and move faster. As the temperature increases, the molecules move even faster and eventually break free from the liquid's surface and escape into the air. This process is known as evaporation. At a certain temperature, known as the boiling point, the vapor pressure of the liquid becomes equal to the atmospheric pressure, causing the liquid to rapidly vaporize and turn into a gas.
The boiling point of a substance varies with altitude due to changes in atmospheric pressure. As altitude increases, the atmospheric pressure decreases, which means that the vapor pressure required for a liquid to boil also decreases. This results in a lower boiling point. For example, water boils at 100 degrees Celsius at sea level, but at a higher altitude, such as on a mountain, the boiling point will be lower, around 90 degrees Celsius.
Yes, the boiling point of a substance can be affected by other factors such as the presence of impurities, the type of container the liquid is in, and the strength of intermolecular forces between the molecules of the liquid. Impurities can raise the boiling point of a substance, while a stronger container can increase the boiling point due to increased pressure. Stronger intermolecular forces can also increase the boiling point by making it more difficult for the molecules to escape into the gas phase.
Water has a higher boiling point than alcohol because water molecules have stronger intermolecular forces compared to alcohol molecules. This means that more energy is required to break these forces and turn the liquid into a gas. Additionally, water molecules are smaller and have a higher molecular weight than alcohol molecules, making them more difficult to vaporize.
Boiling is considered a physical change because the substance does not change chemically during the process. While the molecules are moving from a liquid to a gas state, they are still the same substance. However, if the boiling point is reached due to a chemical reaction, then it can be considered a chemical change. For example, when water boils and turns into steam, it is a physical change. But when ethanol (alcohol) is heated and turns into ethene, it is a chemical change.