Describing Chemical Reactions

Chapter 6.2

Page 224

Section 2:Describing Chemical

ReactionsWhat information does a chemical equation contain?

How is matter conserved during a chemical reaction?

What must a balanced chemical equation show?

What are three types of chemical reactions?

Chemical FormulasThe chemical formula of a compound identifies

the elements in the compound and the ratios in which their atoms are present.

What do the following chemical formulas tell you?

What Are Chemical Equations?

• Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Conservation of Matter

• The principle of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

Conservation of Matter

• In chemical reactions, the number of atoms stays the same. They are just rearranged to form different substances.

6H2O + 6CO2 C6H12O6 + 6O2

water + carbon dioxide glucose + oxygen

PHOTOSYNTHESIS

Balancing Chemical Equations• To describe a reaction accurately, a chemical equation

must show the same number of each type of atom on both sides of the equation.

Balancing Equations Activity

• Click the Active Art button to open a browser window and access Active Art

about balancing equations.

Balancing Chemical Equations

•Magnesium (Mg) reacts with oxygen gas (O2), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element.

Balancing Chemical Equations

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• Balancing Chemical Equations:

– Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

Balancing Chemical Equations

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• Balancing Chemical Equations:

– Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2).

Classifying Chemical Reactions• Many chemical reactions can be classified in

one of three categories: synthesis, decomposition, or replacement. Synthesis – combining

two or more substances to make a more complex substance

Decomposition – breaking compounds down into simpler substances

Replacement – when one element replaces another in a compound

End of Section:Describing Chemical

ReactionsWork on Cornell Notes

for 6.2