BALANCING EQUATIONS & CHEMICAL REACTIONS

Evidence of Chemical Change Changes in Energy (E) Release of E as heat Release of E as light Production of sound Reduction or increase of temperature Absorption or release of electrical Energy Formation of new substances Formation of a gas Formation of a precipitate Change in color Change in odor

Law of Conservation of Mass Same number of atoms on both In any physical or chemical reaction, mass is neither created nor destroyed; it is conserved! Reactants Products Same number of atoms on both sides of the equation!

Balancing Equations In every balanced equation each side of the equation has the same number of atoms of each element

Important stuff! Heat Pressure Temperature Catalyst Four abbreviations are used to indicate physical states of chemicals: shown as subscripts in the chemical equation (s) = solid (l) = liquid (g) = gas (aq)= aqueous solution (dissolved in water) Symbols over the arrow indicate the conditions of the reaction Heat Pressure Temperature Catalyst Reversible reaction

Balance this equation… NaNO3 + CrCl3  NaCl + Cr(NO3)3 How would you “write” it?

Combination Reaction or Synthesis Reaction Two or more simple substances react to form a more complicated one A + B  AB Fe + S  FeS

Combination Reactions We can predict the products of ionic compounds by thinking about the charge! Al (s) + O2 (g)  Cu (s) + S(s)  Are there 2 possible products to this reactions How would we “say” these equations?

Decomposition Reaction A decomposition reaction is the opposite of a composition reaction - a complex molecule breaks down to make simpler ones. AB  A + B 2 H2O  2 H2 + O2

Decomposition Reactions Harder to predict the products…always remember your diatomics. Water is often a product! HgO(s)  NH4NO3

Decomposition Reactions HgO(s)  2HgO(s)  2Hg(l) + O2 (g) NH4NO3  NH4NO3  N2O + 2H2O The only way to really know is to do the reaction!!

Single Replacement This is when one element trades places with another element in a compound. A + BC  AC + B Mg + 2H2O  Mg(OH)2 + H2

Single Replacement Reactions Easy to predict the products. Look at the ions… remember that a cation has to bond to an anion!! Don’t forget about diatomics! Zn(s) + H2SO4(aq)  Na(s) + H2O  OOPS! Did we balance them?

Single Replacement Reactions Zn(s) + H2SO4(aq)  Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) Na(s) + H2O  Na(s) + H+OH-(l)  2Na(s)+ 2H+OH-(l)  2NaOH + H2(g)

Single Replacement Reactions Reactivity of a metal makes a difference! If a metal is more reactive than the metal it is displacing a rxn will occur. If the metal is less reactive than the metal it is displacing, a rxn will not occur.

Metal Reactivity Increases down a group Decreases across a period

Brainiacs-- Metal Reactivity

Reactivity in Single Displacement Cs + KMnO4  CsMnO4 Will this occur?? Na + KMnO4  NaMnO4 + K Will this occur?

Double Replacement Reaction This is when the anions and cations of two different molecules switch places, forming two entirely different compounds AB + CD  AD + CB Pb(NO3)2 + 2KI  PbI2 + 2KNO3

Double Replacement Reactions Generally take place between two ionic compounds in aqueous solution Pb(NO3)2 + 2KI  PbI2 + 2KNO3

Double Replacement Reactions 2NaCl + H2SO4 

Double Replacement Reactions Ca(OH)2(aq) + 2HCl(aq) )

Combustion Reactions A combustion reaction is when oxygen combines with another compound or element producing energy. When hydrocarbons (C?H?) combust, water, carbon dioxide and energy are produced. C10H8 + 12 O2  10 CO2 + 4 H2O + Energy Combustion of Naphthalene

Combustion Reactions Combustion of propane: C3H8 + O2  Combustion of methane: CH4 + O2  Combustion of butene (this one is tricky!) C4H6 + O2 

Teacher Demo Extraordinaire!

What is a flame video- Science Friday http://www.sciencefriday.com/video/06/08/2012/what-is-a-flame.html

Recap: 5 Types of Reactions Combination Decomposition Single Replacement Double Replacement Combustion

Warm Up: Predict the products, balance and classify the following reactions. Li + MgCl2  C6H12 + O2  Ca(NO3)2 + NaOH 

Types of Rxns Lab Take about 10 minutes to do the prelab questions on the lab. Most of the answers should be in your CB notes.

Warm Up- Balance the following combustion equations: C4H4 + O2  CO2 + H2O C3H6 + O2  CO2 + H2O C7H14 + O2  CO2 + H2O

Types of Reaction Lab a. Synthesis: Mg + O2 b. Decomposition CuCO3 c. Single Replacement Zn + HCl d. Double Replacement PbNO3 + KI

Finish the lab You have 20 minutes to get it done! Be sure that all your questions are answered!

Debrief Types of Rxns Lab

Types of Reaction Lab Synthesis: Mg + O2  Did the mass of the system change after the reaction took place? Did you detect the presence of ammonia gas? Endothermic or exothermic? Mass should be greater- MgO Mg + N2 yields Mg3N2 Mg3N2 + H2O yields Mg(OH)2 + NH3

Types of Reaction Lab Decomposition CaCO3  What evidence indicates a chemical reaction. How do you know that carbon dioxide was formed? Endothermic or exothermic?

Types of Reaction Lab Single Replacement Zn + HCl  What evidence did you see? What was in the little tube– how do you know? Endothermic or exothermic?

Types of Reaction Lab Double Replacement PbNO3 + KI  What evidence did you see? Endothermic or exothermic?

Work on classifying the types of reactions on your balancing WS. When you finish, you can start working on the back side of the Current Mole WS…. The front side should be complete!

Warm Up Balance and classify the following reactions: Zn + H2SO4 → H2 + Zn(SO4)2 CaCl2 + NaNO3 → Ca(NO3)2 + NaCl C3H8 + O2 → CO2 + H2O

You should have most of these WS done! Balancing equations WS– classified rxn type 2. Mole Practice WS… Finish both of these… turn them in! Work on the Review! Due the beginning of class on Monday! Test after we go over the review!!

Warm Up Balance and classify the following reactions: Na + H2CO3 → H2 + Na2CO3 2. NaF + Ca(NO3)2 → NaNO3 + CaF2 3. C5H12 + O2 → CO2 + H2O

Warm Up- part 2 Determine the molar mass of MgF2 Convert 5.7 g of magnesium fluoride to moles. Convert 6.3 g of magnesium fluoride to molecules.

Warm Up Quiz Determine the molar mass of Na3PO4 How many moles in 10.6g of Na3PO4 How many atoms in 0.50 mol Al? How many atoms in 3.6 g of carbon?

Warm Up Balance and classify the following reactions: K + H3PO4 → H2 + K3PO4 3. CH12 + O2 → CO2 + H2O