Chapter 6, Sections 1 & 2Pages 214-231.

Describing Chemical Reactions

What is a Precipitate?

A solid that forms from solution during a chemical reaction.

Figure 4, page 218

Endothermic vs. Exothermic

An endothermic reaction takes in energy. (fig. 5, pg. 220) The energy enters.

An exothermic reaction releases energy. (fig. 6, pg. 221) The energy exits.

What are Chemical Equations? An easy way to show a chemical

reaction.Summarize chemical reactions by

using chemical formulas and other symbols.

Figure 8, pg. 225. (draw)

CaCO3 “yeilds” CaO + CO2

Symbol Formula Subscript

Draw!!!

Conservation of Matter During a chemical reaction, matter is neither

created nor destroyed. What other laws does this sound like??? If you can’t destroy matter, can you destroy

atoms?

Open vs. Closed System In an open system, matter can enter from

or escape to the surrounding area. Example: Wood burning in a fireplace. In a closed system, matter cannot enter

or leave. Example: A pear in a glass dome. Figure 10, pg. 227 (draw)

Open System

Balancing Chemical Equations An accurate Chemical equation shows both

sides of the equation equal, having the same number of atoms on each side.

Look at the examples on pages 228-229. Coefficient: A number placed in front of a

chemical formula to balance both sides of the equation. (draw).

Classifying Chemical Reactions The three types of general chemical reactions

are synthesis, decomposition and replacement. (draw)

Figure 11, pg. 230.

Synthesis

When two or more elements or compounds combine to make a more complex substance.

Opposite of Decomposition Figure 11, pg. 230. (draw) Examples: 2H2+ O2 2H2O

2Mg +O2 2MgO

Decomposition Occurs when compounds break down into

simpler products. The opposite of synthesis Figure 11, pg. 230. (draw) Examples:

2H2O2 2H2O + O2

Replacement When one element replaces another in a

compound, or when two elements in different compounds trade places.

Figure 11, pg. 230.

Examples:2Cu2O + C 4Cu + CO2

2Fe2O3+ 3C 4Fe + 3CO2

Questions???