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Melting Point Melting Point by Quan Ho, Athena Tsai, Braden Taylor, Devank Shekhar, Mary Petrino, Luc Sturbelle Definition The temperature at which a solid turns into a liquid. ● Substances enter their phase of equilibrium when they are melting. ● Usually, melting point = freezing point How melting occurs As energy is added in the form of heat, the kinetic energy of the particles increases. The vibrations of the particles become more and more violent until the solid finally begins to break apart or melt. Notes: Even though particles of a solid are packed very closely together in definite structure by their attraction force, these particles do move back and forth and up and down, or vibrate around a fixed point. Chemical Equilibrium A dynamic state in which the rate of the forward reaction equals the rate of the reverse reaction. Chemical Equilibrium (continued) The solid line between points B and D contains the combinations of temperature and pressure at which the solid and liquid are in equilibrium. At every point along this line, the solid melts at the same rate at which the liquid freezes. Facts about melting point of substances ● Pure, crystalline solids melt over a very narrow range of temperatures. ● Mixtures melt over a broad temperature range. Mixtures also tend to melt at temperatures below the melting points of the pure solids. ● An increase of pressure make it easier for the substance to melt, and therefore lowers the melting point. ● The greater the attraction between the particles of a solid, the higher the melting point. Temperature and energy ● Only after the solid is completely melted will the temperature of the substance again begin to rise as additional heat energy is added. ● The amount of energy that must be added to change a solid to a liquid at the melting point is called the heat of fusion (expressed in cal/g) Melting points are often used to identify compounds because…. ● The transition between the solid and the liquid is so sharp for small samples of a pure substance that melting points can be measured to 0.1 Celsius. ● It is difficult, if not impossible, to heat a solid above its melting point because the heat that enters the solid at its melting point is used to convert the solid into a liquid. Real World Examples #1- When you are making glass you have to melt sand. #2- People have to calculate how fast the snow will melt on the mountain in summer and figure out how likely there will be an avalanche and if it’s safe for people to go there. #3- Zookeepers need to make sure that the temperatures in the areas with animals that live in cold weather are cold enough so that the snow and ice won’t melt. #4- When recycled metals are thrown away, they are melted down to make coins and such. For this they need to know what temperature the metals melt at. Investigative Questions #1- Would the rate of melting faster as the substance reaching closer to its melting point? #2- Can radioactive material explode when it reaches melting point? #3- Why does hot water freeze faster than cold water?.
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