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Cara menyetarakan Reaksi 1

The Law of Conservation of Mass:

Every single atom which goes into a chemical reaction MUST come out the other side, even if atoms are grouped differently than when they go in. As an example, consider the problem below. Three red, 2 yellow and 5 blue"atoms" go into the chemical reaction. No matter HOW the atoms are arranged or grouped when they come out the other side, every single "atom" that went in MUST come out the other side. In this case, 3 red, 2 yellow and 5 blue"atoms" MUST come out the other side. Count the number of red, yellow and blue "atoms" on each side of this equation. Do you see that the number of "atoms" of each color on both sides of the chemical reaction is the same? That is the first condition you must meet to have a balanced equation.
Graphic showing 3 red atoms, 2 yellow atoms and 5 blue atoms followed by an arrow showing that the atoms are going into a brown box. The box is labeled 'Chemical Reaction.' Then there is an arrow coming out the other side. On that side there are 4 molecules: one made of 1 red atom and 1 yellow atom, one made out of 1 yellow atom and 1 blue atom, and 2 molecules, each made of 1 red atom and 2 blue atoms. The total number of atoms of each color on each side of the 'Chemical Reaction' box is the same, regardless of how the atoms are arranged. No atoms are gained. No atoms are lost. All are accounted for.

The word "conservation" means that nothing gets lost, and nothing gets created out of thin air. The word "mass" refers to the amount of matter. There is no such thing as "losing atoms" in a chemical reaction. Nor can atoms suddenly appear when they weren't there in the first place.

Coefficients and Subscripts:

The next two bits of information you must learn is how to interpret the two kinds of numbers found in chemical equations. The large numbers in red below are called "coefficients," because they "appear with" the formulas and act as multipliers. ("Co" means "with" and "efficient" comes from a Latin word meaning "to accomplish." So you can think of the coefficient and its formula as "accomplishing together" the balancing of a chemical equation. -- I know, a bit obscure.-- Nevertheless...) The small numbers in blue below are called "subscripts," because they are written below the line. ("Script" for "writing" and "sub" for "below.")
Graphic of equation for the synthesis of water. 2 H2 + O2 ' 2 H2O. The word 'Coefficients' is written above the equation with arrows pointing to the '2' in front of H2 and the '2' in front of H2O. The word 'Subscripts' is written below the equation with arrows pointing to the small '2' after the H in 2 H2, the small '2' written after the O in O2, and the small '2' written after the H in 2 H2O.

Introducing Color Code Formulas

To make learning the meaning of these numbers as easy as possible, we will postpone using real chemical symbols and real chemical formulas until later. For now we will just use colored circles as our "atoms" and the first letters of their color names as our "chemical symbols." For example:
Color Code Key Chart showing representations of 5 different fake elements based on color, along with their chemical symbols. Color names are used for simplicity in discussing coefficients and subscripts in chemical equations. 1 red atom = R. 1 yellow atom = Y. 1 blue atom = B. 1 green atom = G. 1 white atom = W.
Using this Color Code Key, we will clarify the meaning of the two numbers used in chemical equations.

Subscripts Tell How Many Atoms of Each Kind

First of all, the subscript tells us how many atoms of each kind exist in any formula. Look at the examples below. The subscript is ALWAYS written AFTER the symbol of the atom to which it refers.
A series of drawings of atoms and groups of atoms in different connectivities and shapes with their color code chemical formula written beneath, so that a person studying the drawings and symbols could comprehend the meaning of the subscript. Here is a list of the drawings and their accompanying formulas. 1 blue atom B 2 blue atoms stuck together B2 3 blue atoms stuck together B3 1 white atom W 2 white atoms stuck together W2 3 white atoms stuck together W3 2 green atoms stuck together G2 1 green atom G 3 yellow atoms connected in a line Y3 1 red atom R 4 red atoms connected in a 'U' shape R4 7 yellow atoms connected in an 'H' shape Y7
When an atom appears only ONCE in a formula, we do not write the subscript, because it is not needed. If the atom were not there, nothing would be written at all. So the appearance of a symbol in a formula without a subscript tells us that the atom appears there only ONCE.

Combining Two Different "Color" Atoms

What happens when we combine two or more different atoms together? How do we write the formulas then? Study the examples below to see if you can figure it out.
We will write the formula for a molecule made of one atom of blue and one atom of white.
A box combining 1 blue atom and 1 white atom. What formulas do we get? There are 6 variations in drawings, yet all have the same formula. 1 blue and 1 white connected horizontally, with the blue atom 'first.' Formula name is BW or WB. 1 white atom and one blue atom connected horizontally with the white atom 'first.' Formula name is BW or WB. 1 blue and 1 white atom connected vertically with the blue atom on top. Formula name is BW or WB. (Orientation of the molecule doesn't matter. And in color code formulas as we are using, there is no distinction as to which color symbol is written first in a formula, so either answer, BW or WB, is correct.)

In this particular case, since we are only working with colors and not actual element symbols, it does not matter whether we write "B" first or "W" first. Notice also that whichever formula we choose, the formula stays the same, regardless of the molecule's orientation in space.
Now we will write the formula for 1 atom of blue and 2 atoms of white.
A box combining 1 blue and 2 white atoms. Regardless of how the atoms are drawn or connected, their formula is BW2. It could also be W2B. The atoms can be connected in a straight line with the blue atom in the middle or at one end. The molecule can be bent.. The molecule can be oriented differently in space. None of this matters in terms of writing its chemical formula.
In most cases when 1 atom of one kind and 2 of another are put together, the single atom will be the central atom of the molecule, as shown in the first four examples in the box above. The last two examples, in which blue is NOT the central atom, were added to show that the formula describing how many atoms there are of each kind is the same,regardless of how the atoms are connected or how they are oriented in space.
Now we will combine 1 atom of blue and 3 atoms of white.
A box combining 1 blue atom and 3 white atoms. The atoms may be combined in a trigonal shape, with the blue atom in the middle or the atoms may be strung together in a line. The formula remains BW3 or W3B.
In this case, the atoms will almost always connect with each other as shown in the first example, although the second example is still possible. Again, the important lesson to gain from these examples is that the subscript written after a symbol tells how many atoms of that kind there are in the formula. It does not give any information about HOW the atoms are connected to each other.

TAKEN FROM : http://balancingequations.info/

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