1 why water boils at 100 deegry cent grade ? 2 why alchool boils at 78deegrycent grade ?

Question

changes of matter

Answer 1

2 parts to your question:
1.
Temperature is a measure of the kinetic energy of molecules. The higher the temperature, the higher the kinetic energy of the molecules, the more vigorously the particles vibrate.
Boiling involves a change from the liquid to the gaseous state without a change in temperature. For this to happen, the particles would have to have sufficent energy to overcome the a) atmospheric pressure (work done against atm in expansion) and b) the intermolecular forces of attraction.
Therefore, it is only at 100C that water molecules have sufficient energy to overcome these 2 forces. The same applies for alcohol.

2. (why bp water > bp alcohol)
Hydrogen bonding is common to both compounds. The force of attraction is greater in water than alcohol. Water forms 2 hydrogen bonds per molecule, but alcohol only 1 hydrogen bond per molecule.
This means more energy is required to overcome the stronger bonds in water, therefore, water has a higher boiling point.

Answer 2

The reason a liquid boils is because the vapor pressure of the gas vapor on top of the liquid is equal to the pressure of the atmosphere outside.

At any given time, some molecules of the liquid have more energy (on the average) than other molecules and are able to 'break out' of the liquid surface. Now if you introduce heat (energy) by boiling, then you are adding more energy to the molecules to break free. BUT, the capacity to break free is a function of the intermolecular attractions of the liquid molecules with each other. In water, there is a special force called HYDROGEN BONDING bonding; by the very nature of the electronegativity of oxygen in one water molucule next to the the more positive hydrogen in another water molecule. This bonding is intermolecular, (i.e. between molecules) and is stronger in water than in alcohol. Thus, it takes only less heat energy to break free or vaporize alcohol gas molecules. Then, it takes quicker time also to equal the outside pressure so the temperature at which alcohol boils is less than water.

The boiling point is unique for every substance and it is one of the properties to identify that substance.

Answer 3

The reason that water boils at 100 C is that that is the definition of what 100 C is. Alcohol boils at a lower temperature because the intermolecular bonding is weaker than in water.

Answer 4

Water boils at a higher temperature because the forces that hold the water molecules together (hyrdrogen bonding) are stronger so more energy is required. The forces that hold the alcohol together are slightly weaker.

I hope this helps =)

Answer 5

No answer to your question, because there is no such thing as deegry cent grades but you can check out the unit degrees centigrade