Chapter 1.3 Melting and Boiling Flashcards
MELTING
When a solid is heated, the particles gain energy and vibrate rapidly. If the molecules gain enough heat energy/enough heat energy is applied, they break away from their fixed position and the cohesive force of attraction is partly lost, and slightly weakens. This is when the solid changes to a liquid. This process is called melting.
Melting point -
The particular/fixed temperature at which solid turns into liquid is called melting point.
BOILING
When a liquid is heated, the particles gain heat energy and start to vibrate rapidly. If enough heat energy is applied, the molecules break away completely from each other and is separated by a large distance. Then, the cohesive force of attraction is almost lost/negligible. This is when the liquid changes to gas. This process is called boiling.
When heat is given to a substance, a change of state takes place. The reverse change takes place on cooling.
When heat is added –> particles vibrate rapidly –> gain energy
Heat taken away/cooled —> particles vibrate slowly –> lose energy
ABSOLUTE ZERO
As things get colder and colder their molecules move more and more slowly. Eventually at the coldest temperature possible, the molecules hardly move at all. (The particles have the least possible energy here). This temperatyre is called Absolute Zero –> - 273 * C
0 Kelvin = - 273 * C
FACTORS AFFECTING MELTING POINT AND BOILING POINT
There are two ways melting point can be changed:
(1) Adding dissolved materials
(2) Effect of pressure
DISSOLVED MATERIAL
Dissolved materials lower the melting point/freezing point. Salt is an example of a dissolved material. The more salt there is, the lower the melting/freezing point will be. The salt is used to stop water freezing on the rooads.
When salt is added to water it freezes at a temperature colder than
0 * C, sometimes - 3 * C, - 4 * C, or even lower. The salt on the roads lower the freezing point of water. Unless the temperature drops well below 0 * C, no ice is formed and the roads are safe.
EFFECT OF PRESSURE
Increased pressure lowers the melting point
There are two ways of changing boiling point:
(1) Dissolved material
(2) Effect of pressure
DISSOLVED MATERIAL:
Dissolved materials raise the boiling point. When salt is added water boils at a temperature of 120 * C.
EFFECT OF PRESSURE:
a) Increased pressure raises the boiling point
b) Reduced pressure lowers the boiling point
(see Lesson 7 online class new lab copy, flip a few pages for graphs)
graph reference for the rest of the notes:
PQ - the temperature of solid ice rises from - 10 * C to 0 * C (which is the change in temperature)
QR - The temperature remains steady at 0 * C until all the ice turned into water. Melting is taking place
What happens at QR? Why?
Here the temperature remains steady at 0 * C until all the ice turns into water. This is because latent heat causes the change of state of an object without any rise in remperature
RS - The temperature of the liquid (water) rises from 0 * C to 100 * C.
ST - The temperature remains steady at 100 * C until all the water changes to gas/vapour. Boiling is taking place.
Melting Point (M.P) - 0 *
Boiling Point (B.P) - 100 *
During the change of state from ice to water and water to steam, there is no change in temperature even though heat is being absorbed.
Where did the heat go?
It is latent heat that is absorbed into the atmosphere. Latent heat is the hidden heat needed to make a solid melt or liquid boil. Latent - hidden.
