The Heating/Cooling Curve of a Pure Substance

This class' lesson was on the Heating/Cooling curve of a pure substance. Each point on the graph represents a pure substance changing into a new state.


A
-solid state at any temperature below its melting point
-particles packed closely together
-can only vibrate in a fixed position
A-B
-heat energy turns to kinetic energy when heated
-molecules vibrate faster
-temperature increases
B  

-still a solid
-temperature remains the same
B-C
-exists in both solid and liquid state
-temperature remains constant
-contant temperature = melting point
C
-substance has completely melted
-solid has turned into liquid
C-D
-liquid state
-increasing temperature gives heat energy
-particles move faster
D
-exists in liquid state
-molecules start to move freely
-liquid beings to change into gas
D-E
-exists in both liquid and gaseous state
-the temperature remains unchanged
which is the boiling point
E
-liquid has turned into gas
E-F
-gas particles continue to move faster
-temperature increases as heating continues

NOW IT'S TIME FOR SOME TEXTBOOK SUMMARIES!!!!

Finding Out about Matter

Chemists specialize in one of the most important things, matter. So we ask ourselves

• How does one type of matter differ from another?
• What different types of matter have in common
• How one kind can be changed into another or even kept the same

 That is why chemists require unique abilities to make the most detailed observations and analyses.

What YOU Know about Matter

Water is one of the most familar kinds of matter. It's all around us but is it all the same? It acutally comes in all different kinds of forms and types. Water can actually come as a solid, liquid, and even a gas.
If you compare muddy water and water from an ocean, you observe that they look totally different. This is because they are and they both  have different characteristics. Water from different sources can have different tastes and different boiling points.  A boiling point is a temperature in which matter changed from a liquid to a solid.

Purifying Matter

Have you ever noticed that a cup of muddy water continas more than just water? This is called a mixture which are two or more kinds of matter that have separate identities. Matter can be in the form of a mixture or a pure substance. A pure substance is just one kind of matter. In some cases, adding things to pure water like sugar or salt just disappears and does not scatter light. These are called solutions. We know that they taste different but we cannot distinguish if the material is pure from the looks of it.
To find the difference between these two, tests are to be run. They are not ordinary tests, they are tests that separate components. You might ask yourself, how do we do that? It's called distillation; a procedure that evaporates the liquid and leaves produce behind.

Characteristics of a Pure Substance

Pure substances have a constant boiling point and mixures do not.
The temperature at which a liquid changes into a solid is called a Freezing Point
The temperature at which a solid changes into a liquid is called a Melting Point



Chemical and Physical Changes

From the previous posts, we have distinguished the difference between physical and chemicals changes.
Chemical change is irreversible and produce a new kind of matter with different properties.

• This is called decomposition because one kind of matter comes apart to form two or more kinds of matter.

Physical change is reversible and do not appear to produce new kinds of matter.


Compounds and Elements

Electrolysis involves passing an electric current through a substance, causing it to decompose into new kinds of matter
Compounds are pure substances that can be decomposed into new kinds of matter
Elements are pure substances that cannot be decomposed.

Compounds Have a Definite Composition

First of all, there are 2 important rules about compounds

Law of Definite CompositionThis states that all compounds can have any possible composition, but the composition of the compounds must remain the same

Law of Multiple PropertiesThis states different compounds can be made with different amounts of the same elements.