Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. Atoms won’t change their identity (e.g. a Carbon atom can’t become an Iron atom) This means that you have to have the same number of each type of atom on each side of the chemical equation.

Balancing Equations ___ H 2 (g) + ___ O 2 (g) ---> ___ H 2 O(l) 22 What Happened to the Other Oxygen Atom? This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H 2 ) combines with one of the oxygen atoms from an oxygen molecule (O 2 ) to form H 2 O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H 2 molecule) to make a second H 2 O molecule.

Balancing Equations After you write a chemical equation you have to balance it to make sure that the same number of atoms of each element are on each side. How would you balance this equation? Li + H2O  H2 + LiOH

Aluminum metal reacts with liquid bromine to form solid aluminum bromide Translate Equation ___ Al(s) + ___ Br 2 (l) →___ AlBr 3 (s) 2 32

Steps to Balancing a Chemical Equation 6. Check your work 5. Write the Coefficients in their lowest possible ratio 4. Change to Coefficients to make the number of atoms of each element equal on both sides of arrow 2Li(s) + 2 H2O  H2(g) + 2LiOH(aq) 3. Count the atoms of the elements in the products 1 atom Li, 3 atoms H, 1 atom O 2. Count the atoms of the elements in the reactants 1 atom Li, 2 atoms H, 1 atom O 1. Write the Skeleton Equation Li(s) + H2O(l)  H2 (g) + LiOH (aq)

1.calcium fluoride and sulfuric acid make calcium sulfate and hydrofluoric acid 2.calcium carbonate will come apart when you heat it to leave calcium oxide and carbon dioxide. 3.ammonia gas when it is pressed into water will make ammonium hydroxide. 4.aluminum sulfate and calcium hydroxide become aluminum hydroxide and calcium sulfate. 5.copper metal and silver nitrate react to form silver metal and copper (II) nitrate. 6.sodium metal and chlorine react to make sodium chloride. Translate some more!

Types of Reactions There are millions of reactions. Can’t remember them all Fall into several categories. We will be able to predict the products. For some we will be able to predict whether they will happen at all. We will recognize them by the reactants

Synthesis Reactions Also called combination reactions 2 elements, or compounds combine to make one compound. A + B  AB Na (s) + Cl 2 (g)  NaCl (s) Ca (s) +O 2 (g)  CaO (s) SO 3 (s) + H 2 O (l)  H 2 SO 4 (s) We can predict the products if they are two elements. Mg (s) + N 2 (g)  Mg 3 N 2 (s)

Decomposition Reactions decompose = fall apart one compound (reactant) falls apart into two or more elements or compounds. Usually requires energy AB  A + B NaCl Na + Cl 2 CaCO 3 CaO + CO 2

Decomposition Reactions Can predict the products if it is a binary compound Made up of only two elements Falls apart into its elements H2OH2OH2OH2OHgO H 2 (g) + O 2 (g) Hg (s) + O 2 (g)

Decomposition Reactions If the compound has more than two elements you must be given one of the products The other product will be from the missing pieces NiCO 3 (aq) H 2 CO 3 (aq)  + Ni (s) + CO 2 (g) CO 2 (g) H 2 (g)

Combustion A reaction in which a compound (often carbon) reacts with oxygen CH 4 + O 2  CO 2 + H 2 O C 3 H 8 + O 2  CO 2 + H 2 O C 6 H 12 O 6 + O 2  CO 2 + H 2 O

The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction is C + O 2  CO 2

How to recognize which type Look at the reactants Element(E), Compound(C) E + E C Look at the Products CO 2 + H 2 O Synthesis Decomposition Combustion

Examples Synthesis Decomposition H 2 + O 2  H 2 O  HgO 

Examples Decomposition Synthesis CaPO 4  Zn + O 2 

Summary An equation: Describes a reaction Must be balanced because to follow Law of Conservation of Energy Can only be balanced by changing the coefficients. Has special symbols to indicate state, and if catalyst or energy is required.