An Introduction To Chemistry

The science in which substances are examined to find out what they are made of, how they act under different conditions, and how they are combined or separated to/from other substances.

To paraphrase that, Chemistry deals with finding what different substances are made of, what kind of transformations take place, and different chemically related facts about a certain organism or substance.

Physical Chemistry is the study of the patterns of chemical behavior in chemical reactions under various conditions, which result from the chemical and physical properties of substances. Much of physical chemistry involves measurement of some kind. It covers the follwoing:


Factor-label Method

In math you use numbers, in chemistry we use quantities.

A quantity is described by a number and a unit.

100 is a number : 100 Kg is a quantity (notice that in chemistry we give meaning to the numbers). In science we solve a lot of the "math" by watching the units of the quantities

There are two main rules to solving science problems with the factor-label method:

1. Always carry along your units with any measurement you use.

2. You need to form the appropriate labeled ratios (equalities).

Example Problem:

How many centimeters in 2 meters?

You will see from the metric conversion chart that 1 meter = 100 cm

we turn this into a ratio by writing it like this:





Once you have the equalities you must pick the one that will cancel out the units leaving the desired units.

Then multiply your starting quantity (2 meters) by the equality that will give you your desired units.







Practice Problems:

1. How many wheels on 350 Ford pickups (use the equality 1 pickup = 4 tires)

-the starting units are pickups, the ending units need to be wheels.







2. How many millimeters in 34 hectometers (use the equality 10,000 mm = 1 hectometer)?

Sometimes you will need to multiply by more than one ratio to get to your desired units, you can do this by using linking units. Your setup will look like this:








Solids, Liquids, Gases Compared


Solids
The particles of a solid are always arranged in an orderly manner. They have a constant volume, because the particles are so closely packed together, with very little space between them. Compression of a solid to any large extent is not possible because of this tight pack of particles.

Liquids
A fluid is any substance that flows, and liquids are examples of fluids. The particles in liquids are allowed to freely move and change their positions. At all times are the particles moving, moving from neighbor to neighbor. This is why we can 'pour' a liquid into another container. A liquids confinement are the borders of its container. This is why when we pour a liquid into another container, there is conformity to the shape of the container. Compression of a liquid to any large extent is not possible.

Gases
Gases is another example of a fluid, it flows! The particles of gases are however much different than that of solids and liquids. The particles in gases are not neatly arranged, and they don't even touch each other most of the time. There is lots of space in between particles, which is why when put in a container, it is filled with the gas. And when released from a container, the gas is dispersed. The particles in gases are always moving, just like the particles in a liquid.

Types of Chemical reactions

Combustion
A combustion reaction is when all substances in a compound are combined with oxygen, which then produces carbon dioxide and water. Combustion is commonly called burning. It is an exothermic reaction, which means heat is produced and is easily distinguished. Combustion occurs predominantly in automobiles, homes, and in factories. An example of a combustion reaction is as follows:

CxHy + O2 --> CO2 + H2O


Synthesis
A synthesis reaction is when there is a combination of two or more substances and a compound results. An example of a synthesis reaction is as follows:

A + B --> AB


Decomposition
Decomposition is the opposite of synthesis. It is when a compound is broken down into simpler substances, usually through electrolysis. An example of decomposition is as follows:

AB --> A + B



Dissociation
Dissociation is commonly mistaken as decomposition, but there is a difference. When the compound is broken down, it is broken down into ions rather than atoms, so there will be a charge on the product side of the equation. An example of dissociation is as follows:

AB --> A+ + B



Single Replacement Reactions
In a single replacement reaction, there is a rule that is always followed. A metal replaces a metal, or a nonmetal replaces a nonmetal. An example of a single replacement reaction is as follows:

A + BC --> AC + B




Double Replacement Reactions
In a double replacement reaction, this rule is always followed. A metal replaces a metal, and a nonmetal replaces a nonmetal. An example of a double replacement reaction is as follows:

AB + XY --> AY + XB