Chemical Reactions Unit 7, Chapter 7

I. Chemical reaction: Occurs when one or more substances undergo a chemical and physical change producing one or more new and different substances.

II. Indicators of a chemical reaction A. A gas is produced- effervescence B. A solid is produced- precipitation C. Energy is released- exothermic

D. Energy is absorbed- endothermic E. Color change

III. The Chemical Equation A. A written expression representing a chemical reaction. B. Parts of a chemical equation: N 2 H 4 + O 2 N H 2 O reactants products yields or produces H2OH2OH2OH2O coefficient subscripts

C. Reading the chemical equation Fe 2 O 3 + CO CO 2 + Fe iron (III) oxide and carbon monoxide produce carbon dioxide and iron

D. Balancing the chemical equation 1. Law of conservation of mass- matter cannot be created or destroyed in a chemical reaction 2. There must be the same number of each element on either side of the chemical equation Ca + H 2 O Ca(OH) 2 + H 2 1 Ca atom 2 H atoms 2 O atoms 4 H atoms 2 A Balanced Equation!

Let’s try two more! CH 4 + O 2 CO 2 + H 2 O N 2 + Cl 2 NCl 3 2 N atoms6 Cl atoms1 N atom 2 2 N atoms 6 Cl atoms 2 Cl atoms 3 1 C atom 4 H atoms2 H atoms4 H atoms 2 2 O atoms 4 O atoms 2

IV. Basic types of chemical reactions A. Synthesis DEMO TIME!!! 1. Two or more simple substances combine to produce a single product 2. A + B AB 3. A + B + C ABC

B. Decomposition 1. A single reactant breaks down into two or more simpler substances 2. AB A + B DEMO TIME!!! 3. ABC A + B + C

C. Single Replacement 1. An element replaces a similar element in a compound 2. A + BC AC + B (if A is a metal) DEMO TIME!!! 3. A + BC BA + C (if A is a nonmetal)

D. Double Replacement 1. Two different compounds exchange positive ions and form two new compounds 2. AB + CD CB + AD DEMO TIME!!!

E. Combustion 1. An organic substance reacts with oxygen producing carbon dioxide and water 2. ______ + O 2 CO 2 + H 2 O DEMO TIME!!!

F. Neutralization 1. An acid and a base react to produce salt and water 2. HX + AOH AX + HOH (acid) (base) (salt) (water) DEMO TIME!!!

V. Energy in a chemical reaction A. Energy is stored in chemical bonds 1. A bond releases energy when broken in an exothermic reaction B. Activation Energy 2. A bond needs energy to break in an endothermic reaction 1. Energy needed to start a reaction 2. Example: a spark is needed to get a fire started C. Energy is always conserved Total energy before = total energy after

VI. Collision Theory A. Molecules must collide in order to react B. The more collisions there are, the faster the reaction goes.

VII. Things that affect reaction rate A. Concentration: The more molecules there are, the more collisions there are. B. Surface Area: A large surface area increases the chance for collisions. C. Temperature: Warmer temperatures cause molecules to move faster and collide more often. D. Stirring: Causes the molecules to move faster and collide more often. E. Catalyst: Causes the reaction to go faster just by being present. A catalyst does not react itself.