Notes for Monday, Jan. 4, 2010

• A chemical reaction is the process by which one or more substances are changed into one or more different substances.
• In any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products.
• According to the law of conservation of mass, the total mass of the reactants must be equal to the total mass of the products for any given chemical reaction.
• A chemical equation represents, with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction.
• Example: The following chemical equation shows that the reactant ammonium dichromate yields the products nitrogen, chromium (II), and water.

(NH₄)₂Cr₂O_7- (s) --> N₂ (g) + Cr₂O₃ (s) + 4 H₂O (g)

• The symbols in parentheses state the form of the substance. q represents an aqueous substance. If a catalyst is needed to produce a reaction, it will be written with the arrow.

Indication of a Chemical Reaction

• Certain easily observed changes usually indicate that a chemical reaction has occurred.

1. Evolution of energy as heat and light.
2. Production of a gas
3. Color change
4. Formation of a precipitate.

• A solid that is produced as a result of a chemical reaction in a solution and that separates from the solution is known as a precipitate.

Characteristics of Chemical Equations

• The following requirements will aid you in writing and reading chemical equations correctly.

1. The equation must represent known facts.
2. The equation must contain the correct formulas for the reactants and products.
3. The law of conservation of mass must be satisfied.

• A coefficient is a small whole number that appears in front of a formula in a chemical equation.

Elements That Normally Exists as Diatomic Numbers

1. Hydrogen
2. Nitrogen
3. Oxygen
4. Fluorine
5. Chlorine
6. Bromine
7. Iodine

• Memory aid: seven elements, and the ones that aren't hydrogen form a seven on the periodic table.

Word and Formula Equations

• The first step in writing a chemical equation is to identify the facts to be represented.
• A word equation is an equation in which the reactants and products in a chemical reaction are represented by words.
• A word equation is qualitative.
• Example: methane + oxygen --> carbon dioxide + water.
• The next step in writing a correct chemical equation is to replace the names of the reactants and products with appropriate symbols and formulas.
• A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas.

Example: CH₄ (g) + O₂ (g) --> CO₂ (g) + H₂O (g)

• To complete the process of writing a correct equation, the law of conservation of mass must be taken into account.
• The relative amounts of reactants and products represented in the equation must be adjusted so that the numbers and types of atoms are the same on both sides of the equation.
• This process is called balancing the equation and is carried out by inserting coefficients.

Once again, I'm going to give people the chance to volunteer to do tomorrow's blog or I'll use a random number generator to pick who gets it. Since lots of people asked me about this, feel free to check it out yourself at http://www.random.org/.

Have a good night,

Your Friendly Neighborhood Jim