Chemical Equations Pb(NO3)2 + 2 KI PbI2 + 2 KNO3

Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

Evidence of Chemical Reactions Formation of a precipitate (solid) Production of gas Unexpected color change Heat, light, and/or flame is produced Change in odor https://www.youtube.com/watch?v=nsEkKIiOz7Q https://www.youtube.com/watch?v=NR5VFh2D6hs

Chemical Equations Chemical reactions are expressed by chemical equations. Chemical equations identify the reactants (starting chemicals) and the products (ending chemicals). The reactants are always on the left side of the equation, and the products are on the right side. Coefficients are used to show the molar ratios of the reactants and products.

Chemical Equations coefficients 2H2 + O2 2H2O reactants products

Learning Check Identify the reactants, products, and the coefficients in the following examples: AgNO3 + NaCl AgCl + NaNO3 2 AB + 2 C2D 2 AD + 2 C2B

A Chemical Reaction Reactants Products

Learning Check A. How does an equation indicate a change in the identity of the reacting substances? B. How did the yellow and pink reactants combine? C. Did all the reactants form product? How can you tell?

Learning Check A. How does an equation indicate a change in the identity of the reacting substances? The formulas of the reactants are different than the formulas of the products. B. How did the yellow and pink reactants combine? 1 yellow combined with 1 pink. C. Did all the reactants form product? Why or why not? No. There were more pink reactants than yellow.

Writing a Chemical Equation Chemical equations give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide react to form carbon monoxide plus carbon and magnesium

Reading A Chemical Equation 4 NH3 + 5 O2 4 NO + 6 H2O Four molecules of NH3 react with five molecules O2 to produce four molecules NO and six molecules of H2O OR Four moles NH3 react with 5 moles O2 to produce four moles NO and six moles H2O

Balanced Chemical Equations Same numbers of each type of atom on each side of the equation Al + S Al2S3 Not Balanced 2Al + 3S Al2S3 Balanced

Matter Is Conserved total reactant atoms = total product atoms H2 + Cl2 2 HCl + + total reactant atoms = total product atoms 2H, 2Cl 2H, 2Cl total reactant mass = total product mass 2(1.0) + 2(35.5) 2(36.5) 73.0 g/mol = 73.0 g/mol

Law of Conservation of Mass Matter is neither created nor destroyed in a chemical reaction. Matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant. Whenever matter undergoes a change, the total mass of the products of the change is, within measurable limits, the same as the total mass of the reactants.

Balance Equations with Coefficients Coefficients are used to balance each type of atom 4NH3 + 5O2 4NO + 6H2O 4 N = 4 N 12 H = 12 H 10 O = 10 O

Learning Check Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O 1) 2 2) 4 3) 8 B. Number of O atoms in 4 H2O C. Number of Fe atoms in Fe3O4 1) 1 2) 3 3) 4

Learning Check Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O 3) 8 B. Number of O atoms in 4 H2O 2) 4 C. Number of Fe atoms in Fe3O4 2) 3

Learning Check Balance each equation: A. Mg + N2 Mg3N2 B. Al + Cl2 AlCl3 C. Al + FeO Fe + Al2O3

Learning Check Balance each equation: A. 3Mg + N2 Mg3N2 B. 2Al + 3Cl2 2AlCl3 C. 2Al + 3FeO 3Fe + Al2O3

Reaction Types Most chemical reactions can be placed into one of five basic types: Synthesis Decomposition Single replacement Double replacement Combustion

Synthesis Reactions Elements are joined together OR Compounds are joined together   2H2 + O2 → 2H2O  

Decomposition Reactions A compound breaks into parts.   2H2O → 2H2 + O2

Single Replacement Reactions A single element replaces an element in a compound.   Zn + 2HCl → H2 + ZnCl2

Single Replacement Reactions (cont’d) The number of dancers has not changed, but the lady switched her partner. Note that like replaces like. In the example, a female will replace a female. In a chemical reaction, a cation will replace a cation.

Double Replacement Reactions Two elements from two different compounds switch places.   H2SO4 + 2NaOH → Na2SO4 + 2H2O

Double Replacement Reactions (cont’d) Note that like replaces like. In the example, the men change hats. In a chemical reaction, a cation swaps with a cation, and an anion swaps with an anion.

Combustion Reactions A hydrocarbon (a compound containing only carbon and hydrogen) combines with oxygen.   The products of combustion are always carbon dioxide and water.   hydrocarbon + oxygen → carbon dioxide + water   CH4 + 2O2 → CO2 + 2H2O Often gives off heat and light

Visual Summary of Reaction Types

Learning Check Identify each type of reaction: a) 2NaBr + Ca(OH)2 2NaOH + CaBr2 b) P4 + 3O2 2P2O3 c) C3H6O + 4O2 3CO2 + 3H2O d) 2NO2 N2 + 2O2 e) Pb + FeSO4 Fe + PbSO4

Learning Check Identify each type of reaction: a) 2NaBr + Ca(OH)2 2NaOH + CaBr2 Double replacement b) P4 + 3O2 2P2O3 Synthesis c) C3H6O + 4O2 3CO2 + 3H2O Combustion

Learning Check Identify each type of reaction: d) 2NO2 N2 + 2O2 Decomposition e) Pb + FeSO4 Fe + PbSO4 Single Replacement

Equations with Polyatomic Ions Polyatomic ions are ions composed of multiple atoms which are covalently bonded Examples: CO32- and NH4+ Often the polyatomic ions will remain unchanged during a reaction.

Writing Formulas with Polyatomic Ions Polyatomic ions often have subscripts of their own, as in the SO42- ion. Parenthesis surround the formula of the polyatomic ion when there is more than one. Al2(SO4)3 NOT Al2SO43

Learning Check How many Al, S, and O atoms are present in each of these formulas? Al2(SO4)3 Al2SO43 Al = Al = S = S = O = O =

Learning Check How many Al, S, and O atoms are present in each of these formulas? Al2(SO4)3 Al2SO43 Al = 2 Al = 2 S = 3 S = 1 O = 12 O = 43

Learning Check How many SO42- are present in the molecule Al2(SO4)3?

Learning Check How many SO42- ions are present in the molecule Al2(SO4)3? There are 3 (SO42-) ions

Balancing Equations with Polyatomic Ions When a polyatomic ion appears in both the reactants and the products (meaning it does not change during the reaction) it can be treated as an atom. 2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Treat (NO3-) as if it were an atom Treat (SO42-) as if it were an atom As always, use only the coefficients to balance the equation!

Learning Check 2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Al = Al = *NO3- = *NO3- = H = H = *SO42- = *SO42- = * Treated as an atom

Learning Check 2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Al = 2 Al = 2 *NO3- = 6 *NO3- = 6 H = 6 H = 6 *SO42- = 3 *SO42- = 3 *Treated as an atom

Learning Check Balance the following equations: __NaHCO3 __Na2CO3 + __CO2 + __H2O __Al2(SO4)3 + __Ca(OH)2 __Al(OH)3 + __Ca(SO4)

Learning Check Balance the following equation: 2NaHCO3 Na2CO3 + CO2 + H2O Al2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3Ca(SO4)