Flashcards Included in this Note

1. Important Terms/Concepts

1. Chemical Reaction--a process during which one or more reactants are changed into one or more products.

2. Reactants --the original substances that existed before the chemical reaction took place.  The reactants are normally found on the left side of a chemical reaction equation arrow (yields sign).

3. Products--the substances that were produced during the chemical reaction.  The products are normally found on the right side of a chemical reaction equation arrow (yields sign).

4. **Law of Conservation of Matter--**Matter is neither created nor destroyed but can be transformed or transferred.  In a chemical equation, this means that the number of atoms of each element in the equation must be equal on both sides of the reaction arrow.

5. **Balanced equation—**a chemical equation in which the number of atoms of each element in the equation is equal on both sides of the yields sign.

6. **Skeleton equation—**a chemical equation that is not balanced. This type of equation lists the reactants and products, but not the relative numbers of each that are present.

7. Catalyst—a substance which speeds up a chemical reaction but is not changed by the reaction. Catalysts are not reactants or products.

8. Coefficients—small whole numbers that are placed in front of the chemical formulas in an equation in order to balance the equation. The coefficients indicate the number of moles, molecules, or formula units of the indicated chemical.

For example: Ca(OH)2 + (NH4)2SO4 à CaSO4 + 2NH3 + 2H2O

Reactants                                Products

Ca atoms = 1                          Ca atoms = 1

N atoms = 2                            N atoms = 2

S atoms = 1                             S atoms = 1

H atoms = 10                         H atoms = 10

O atoms = 6                           O atoms = 6

1. Balancing Chemical Reactions:

1. Identify the reactants and products for the chemical reaction.

2. Write the skeleton equation for the reaction.

3. Count atoms & balance each element (one at a time) by changing coefficients.  Do not change          the formula subscripts.   Changing the subscripts changes the identity of the chemical.

4. Double check by recounting elements (as seen in the above example) for your final reaction equation.

5. Make sure that all coefficients are in the lowest possible ratio.  If they are not, reduce them using the same method used to reduce fractions.

• Symbols Associated with Chemical Reactions

Symbols often associated with chemical reactions:

1. --> means “yields”.

2. <--> means “reversible reaction” or “equilibrium”.

3. (s) – substance is in a solid state.

4. (l) – substance is in a liquid state.

5. (aq) – substance is aqueous (means “dissolved in water”).

6. (g) – substance is in a gas state.

7. “Δ” or “heat” on top of the arrow – means reactants are heated.

8. “atm” on top of the arrow – means reactants are under pressure.

9. “0C” on top of the arrow – indicates the reaction temperature.

10. “ chemical name” on top of the arrow – indicates a chemical catalyst is present.

1. Evidence that a Chemical Reaction Occurred

2. Generation of light.

3. A temperature change takes places within the reaction “chamber”.

4. Endothermic – absorbs heat energy from the environment. (Temperature decreases, feels cold.)

5. Exothermic – releases heat energy to the environment. (Temperature increases, feels warm.)

6.  Production of a gas. (Bubbles are seen, or odor is detected.

7. Formation of a precipitate. A precipitate is a solid that is produced when liquids are mixed.

8. A color change takes place.