Chapter 8 Notes

Chemical Equations and Reactions

I. Describing chemical reactionsA. Chemical equations describe chemical

reactionsB. Evidence that a chemical reaction has occurred

1. Heat and/or light given off2. Gas produced3. Precipitate-an insoluble product formed by the

reaction of two solutions4. Color change

C. These elements exist as diatomic molecules and must be written with a subscript of two when not in a compound.

H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

They are referred to as HOFBrINCl elements.

D. Coefficients are written in front of symbols and formulas to satisfy the Law of Conservation of Mass (balance the equation).

E. Word Equation

Iron + Oxygen Iron (III) Oxide (Reactants) (Products)

F. Formula Equation (Not Balanced)

Fe + O₂ Fe₂O₃

G. Balanced Equations

____ Fe + ____ O₂ ____ Fe₂O₃

____ ________ + ____ ________ ____ ________ + ____ ________ Iron (III) Calcium Iron (III) Calcium Chloride Hydroxide Hydroxide Chloride

H. Other symbols (P. 246 –learn them!!!) may be used in a chemical equation.

I. Catalyst – A substance used to change the speed of a reaction, but which is not used up

MnO₂

2 H₂ O2 -------- > 2H₂O + O₂

J. Coefficients indicate relative amounts of reactants and products.

2 H₂ + O₂ 2H₂O

2 molecules 1 molecule 2 molecules 2 moles 1 mole 2 moles

2[(1.01)(2)]g + (16.00)(2)g = 2[(1.01)(2)+(16.00)] g 4.04g + 32.00g = 36.04g

Types of Chemical Reactions

A. Synthesis1. Two or more substances combine to form one

compound.2. __ ________ + __ ________ __ ________ Aluminum Oxygen 3. __ ________ + __ ________ __ ________ Carbon Dioxide Water Carbonic Acid4. __ ________ + __ ________ __ ________ Phosphorus Oxygen Diphosphorus Pentoxide

B. Decomposition Reactions

1. A compound breaks down into simpler substances.

2. __ ________ __ ________ + __ ________ Mercury (II) Oxide

3. __ ________ __ ________ + __ _______ Calcium Carbonate Calcium Oxide Carbon Dioxide

C. Single Replacement Reactions

1. An Element replaces a similar element in a compound

2. __ _____ + __ _____ __ _____ + __ ______ Magnesium Hydrochloric Acid

3. __ ______ + __ ______ __ ______ + __ ______ Potassium Iodide Chloride