How does the boiling point of water change by dissolving a substance into the water? How does the freezin?
355097
Simply it will raise the boiling point and lower the freazing point.  Unless the solute is a liquid with a boiling point bellow that of water when the boiling point will go down.\n\nMore complecatedly. When something disolves in water its molecules bind to the molecules of water creating a solvation shell (a group of water mollecules that move with the solute) for the water to boil you need to strip these molicules away from the solute which takes energy and hence the  boiling point goes up. For a liquid with a lower boiling point than water the molecules of the solute will be lost first (but above its boiling point) and some water will go with them (distilation of alcohol being the classic example). \n\nFor water to freaze the water molecules must bind to each other to form crystals of ice which creates order and gives out energy. If a substance is disolved in the water then again you must break the bonds between the solute and the water to do this. This means you get less energy from forming the water-water bonds in the crystal as you have used it to break the water-solute bond. Now if a process is to create order within a system (the solution) it must make more disorder elsewhere (the rest of the world). This is called the second law of thermodynamics (the law is stated diffrently but this is one consequence of it). So if the energy we given out when the water freazes is reduced so is the amount of disorder it creates. However as the temp goes down the amount of order we create is reduced as the molecules of water move more slowly and so are more "ordered" to start with. So when the amount of order we create is equal to the amount of disorder the energy relased by freazing will produce the water freazes. So as the amount of energy relased is reduced so the tempreature when this is true becomes lower.
947849
The higher the altitude, the lower the atmospheric pressure. The less atmospheric pressure that bears down on the surface of the liquid, the easier it is for water molecules to escape into the air. Thus, the water comes to its full rapid boil at a lower temperature in the mile-high city of Denver than it can in coastal Miami. For each thousand feet above sea level, the boiling point of water drops almost 2° F.
475683
solutes such as ions, greatly increase boiling point and reduce the freezing point thank you\n\nexplaination... have things to do with attraction between molecules and bonding..
403230
It takes quite a lot of energy for water to change phase.  Steam actually contains much more energy than does boiling water, therefore it burns far worse when it comes in contact with human skin.\n\nSee the link below.  You can actually do the math to confirm this -- it takes 100 cal/gm to heat water from 0 to 100 degrees C, but 539 cal/gm to change that water into steam.  So ten grams of water at 0 degrees C absorbs 1000 calories to boil but nearly 6400 calories to turn completely into steam.\n\nThat's a lot of heat.\n\nIn rebuttal to some of the other answers, burns are caused (I believe) by heat convection -- that is, the hot substance in direct contact with the skin, transferring its heat to the skin cells and damaging or destroying them.  Water is more likely to stay in contact with the skin than steam is, because steam is a gas that rises away from the skin.  This is why some people seem to erroneously believe that steam doesn't burn.\n\nHowever if skin comes into continuous contact with steam, it will burn, and quite badly.
137058
the difference in the boiling point of this soln compared to pure water equals Kb times m, where Kb is the boiling point constant(0.512 for water) and m is the molality of the soln.\nso the answer si 100.512 degrees C.
15822
It mainly depends on the pressure (if we are talking about pure water). The higher the pressure, the higher the boiling point - it can be much lower (ex. high in the mountains) or much higher than 100 degrees C (the boiling point under normal atmospheric pressure). If we don't talk about pure water, then adding other chemicals (for example, table salt - sodium chloride) can raise the boiling point as well.
432980
Look in the index of an introductory chemistry text for "colligative properties", "freezing point depression", or "boiling point elevation".  Simply put, the water molecules prefer to orient themselves around the sodium and chloride ions instead of each other.  This lowers the freezing point (more energy has to be removed from the system to slow down the molecules enough to be in the solid state.  This effect also accounts for the boiling point elevation (salty water boils at a higher temp) and for the same reason.
232411
Salt only helps the boiling point rise a little. It will boil more rapidly. It will not decrease time it takes to reach boiling point.
82527
This is not chemistry, but physics. I presume you are boiling water in a can, then sealing it and cooling it. There is then less pressure inside the can, since the water takes up less space than the water vapor. There is now more pressure outside the can than inside the can. You have unbalanced forces, and the can is unable to resist the pressure.\n\nThis can of course get far more complicated, and we can discuss the ductility of the can, and continuum mechanics of the can, and its chemistry, but I do not think you want anything that advanced. If you do, let me know.
837121
Hmmm.. The one affecting the boiling point is the intermolecular force..\nAs you can see, most of the compound here is polar. \n\nTherefore all you have to do is if the compound is consisted only of 2 elements (Group 17), you'll have to calculate the electronegativity difference. The more difference between them, the boiling will increase as well.\n\nIf there is more than 2 atoms in a molecule, you'll have to see the dipole moment magnitude (a.k.a polarity). The higher the magnitude, the higher the boiling point will be.\n\n\npeace\nvixklen
356469
The lower the air pressure, the lower the boiling point of water.
247971
From what I was TOLD,\nGlass doesn't have an observable melting point. If you've seen a graph of temperature of a substance plotted against the time it is heated constantly, you'd know what 'observable' means. A substance (e.g. water) may STAY at two temperatures (0C & 100C for water) for some time even though it never stops being heated. For water the lower temperature is when ice melts and the higher when water boils, and they are called melting/boiling points respectively.\n\nDuring the time 'solid' glass is heated till it is clearly liquid, no such temperature-halt is observed, so they say glass has no observable melting point.\n\n[edit] I too prefer the way calling glass a liquid. Since it's already concisely mentioned, I added quotation marks around the word 'solid', intending to express glass appears to be solid but it may well be an extremely thick liquid.
229195
When you add a salt to water and the container feels cold, yes, an endothermic reaction is taking place.  The solution is grabbing heat from the surroundings to get the salt to dissolve.  When you add a salt to a pure solvent (say, water), the freezing point will go down and the boiling point will go up.  That's because the vapor pressure of the pure solvent is lowered (this would be easier to explain with a phase diagram).  Remember, the definition of BP is the temp at which the solution's vapor pressure equals the external pressure.  By lowering the vapor pressure, the whole phase diagram shifts...BP to the right (higher), FP to the left (lower).  You may want to check out a intro level chemistry text or at least draw out the phase diagram to see more clearly what gets lost is just words here.  Did you ever try boiling water without heating it?  If you have the means, hook up a vacuum to a flask of water.  You don't change the vapor pressure of the water, but you reduce the external pressure enough so that the water does boil.\n\nOne more thing...  The change in BP and FP is related to how much salt is added to the solvent:  delta T (change in T) = Km  where K is either what's called the molal freezing-point depression constant or molal boiling-point elevation constant;  m is the molality of the solution defined as moles of solute (salt) / kilograms of solvent. By knowing the constant for the solvent, how much solvent you have and how much solute you add, you can predict by how much (in degrees (C) the BP or FP will change.\n\nI would just like to add a couple of more comments... The reaction that is endothermic in this case is  NaCl(s) --> Na+(aq) + Cl-(aq)  ...  The reason that the freezing point is lowered is as J. Schultz said - the vapor pressure is lowered ....  However there is a simple analogy (that may be useful) which gives a simplified picture ... Freezing involves the water molecules becoming very ordered in crystalline lattice...  However when there are foreign particles such as Na+ and Cl- ions in the water they hinder the formation of the crystalline structure because they interfere with the intermolecular forces between the water molecules.  Also, the freezing point depression and boiling point elevation are called colligative properties...  that is, they are properties that depend only on the number of solute particles and not on their chemical properties...  The third famous colligative property is osmotic pressure.
469334
Because salt consists of sodium and chloride ions, and as You know, ions have charge, so You know there will be an interaction(attraction) between water molecules and the ions. You might also know that in ice, water molecules are in a definite distance from each other, they are in a crystal structure. Well, because of the interaction, that structure "opens up", and the water molecules get closer to each other, so the structure move from solid to liquid, as the interaction between them becomes weaker.\nI hope i was understandable. \nSalt lowers the boiling point and increases the freezing point of water. You can see it Yourself by putting salt into water, it'll boil sooner than without it.
124074
In short: Any solution will boil at a higher temperature than the pure solvent. \nBoiling point elevation is a colligative property. Use the formula provided by emilyrose. The addition of salt to water causes vapor pressure reduction of the water. This is because the addition of a non-volatile solute causes a reduction in the surface area available to water molecules, reducing the likelihood of evaporation. This vapor pressure lowering is described by Raoults Law (see link).\nInterestingly, if you have a salt solution, and you heat it till it boils, as the water evaporates, the boiling temperature of the solution will continuously increase, because its molality increases. Please see the link below for a more detailed discussion.
134246
The Latent heat of Fusion and Latent heat of Vaporization refer to how much energy must be put into a substance (or taken out) in order to change its phase after it has reached its melting/boiling points respectively.\n\nTake water for example [boiling point 100 C, melting point 0 C].\nWhen you are boiling water, the temperature continues to increase until it seems to stop at 100 degrees C.  At this point, water begins to boil and until all the water has boiled off, the temperature will remain constant.  However, obviously, energy is still being put into the system (that is what is causing it to boil) but you dont see a temperature increase.  This enegry is going directly into boiling water, not increasing its temperature, thus it is somewhat "hidden".\n\nNow take water freezong into ice.  As water is cooled dowbn, its temperature will decrease until it reaches 0 degrees C.  At this point water is still a liquid, but is on the verge of becoming ice.  In order to make that liquid water into solid ice, additional energy need to be taken out of it, the Latent heat of fusion.  All the while, as the water freezes, its temperature stays a constant 0 degrees C, it will not continue to decrease until the watrer is frozen.
24100
These effects are sometimes called colligative properties in text books. The effect is entropic in origin but the precise description gets kind of hairy without a background in thermodynamics. Basically, there is a driving force called the mixing entropy, for water molecules to stay in a heterogeneous phase like a salty solution rather than a homogeneous phase like pure ice or water vapor. In the case of boiling point elevation, this means more energy must be put into the system to drive water molecules into the vapor phase. In the case of freezing point depression, this means that water molecules will tend to the liquid rather than solid phase.