Describing Chemical Reactions Chapter 6.2 Page 224

Section 2: Describing Chemical Reactions What 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 Formulas The 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 Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

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 Reactions Work on Cornell Notes for 6.2