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? Name the three types of chemical reactions. √ √

Chemical Formulas The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

What Are Chemical Equations? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Reviewing the Law of Conservation of Matter Matter is neither created nor destroyed *It is simply rearranged!

Conservation of Matter The law of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. (aka conservation of mass)

Open and Closed Systems

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.

Coefficients

Let’s try some! 3 3 ____ AlBr3 + ____ K  ____ KBr + ____ Al Count the atoms: 1 Aluminum atom 1 Potassium atom 1 Potassium atom 1 Aluminum atom 3 Bromine atoms 1 Bromine atom Is it balanced? No! Add coefficients to balance atoms: 1 Aluminum atom 3 Potassium atoms 3 Potassium atoms 1 Aluminum atom 3 Bromine atoms 3 Bromine atoms Is it balanced? YES!

Let’s try some! ____ FeO + ____ PdF2  ____ FeF2 + ____ PdO Count the atoms: 1 Iron 1 Palladium 1 Iron 1 Palladium 1 Oxygen 2 Flourine 2 Flourine 1 Oxygen Is it balanced? YES! Do we need to add coefficients? NO!

Let’s try some! 6 4 ____ P4 + ____ Br2  ____ PBr3 Count the atoms: 4 Phosphorus 2 Bromines 1 Phosphorus 3 Bromines Is it balanced? No! Add coefficients to balance atoms: 4 Phosphorus 12 Bromines 4 Phosphorus 12 Bromines Is it balanced? YES!

Let’s try a harder one! 2 3 3 ____ CoBr3 + ____ CaSO4  ____ CaBr2 + ____ Co2(SO4)3 Count the atoms: 1 Co 1 Ca 1 Ca 2 Co 3 Br 1 S 2 Br 3 S 4 O 12 O Is it balanced? No! Add coefficients to balance atoms: 2 Co 3 Ca 3 Ca 2 Co 6 Br 3 S 6 Br 3 S 12 O 12 O Is it balanced? YES!

Classifying Chemical Reactions 1. Synthesis: Two or more elements or compounds combining to make a more complex substance 2. Decomposition Compounds break down into simpler products (hydrogen peroxide decomposes to water and oxygen gas) 3. Replacement One element replaces another in a compound or two elements in different compound trade places (Copper can be obtained by heating copper oxide with carbon. The carbon takes the place of copper.