Chemistry – Feb 1, 2017 P3 Challenge – Translate this sentence into a balanced equation including state descriptors: If chlorine gas is bubbled through an aqueous solution of hydrosulfuric acid, solid elemental sulfur is formed within an aqueous solution of hydrochloric acid. Today’s Objective – Driving forces for reactions Get out Word Equations and types on Balancing Worksheet for HMK check

Chemistry – Feb 1, 2017 Objective – Driving forces Assignment: Driving forces worksheet Agenda Homework Review Types of driving forces Precipitation reactions Solubility rules Net ionic equations Acids and bases Neutralization reactions

Driving Force We can write many kinds of reactions on paper, but for them to actually occur, there must be some kind of driving force. Otherwise a simple mixture will happen with no reaction. Driving Forces: Formation of a solid Formation of water Formation of a gas Transfer of electrons Determines a second classification Note: Any given reaction may have more than one driving force. But if it has none, it will not happen.

1) Formation of a solid When two ionic solutions are mixed… Sometimes a solid forms. Reaction happens. Solid formation is a driving force. Called a precipitation reaction. Sometimes no reaction happens. How do you know which? Experiments. Patterns: Solubility rules Chapter 7, Unnumbered Figure 1, Page 219

Solubility Rules All common compounds of alkali and ammonium ions are soluble. All nitrates, acetates, and chlorates are soluble. All binary compounds of the halogens with metals are soluble, except those of Ag, Hg(I), Pb. All sulfates are soluble, except those of Ba, Ca, Sr, Ag, Hg(I), Pb. Carbonates, hydroxides, oxides, and phosphates are insoluble, except for alkali and ammonium ions. Sulfides are insoluble except for Ba, Ca, Sr, Mg, alkali and ammonium.

Li+, Na+, K+, NH4+ (primary rule) Solubility Rules Soluble Insoluble (Precipitates) Li+, Na+, K+, NH4+ (primary rule) NO3-, C2H3O2-, ClO3- Cl-, Br-, I- Ag+, Hg22+ , Pb2+ SO42- Ba2+, Ca2+, Sr2+ CO32-, O2-, PO43- OH- Ba2+, Ca2+, Sr2+, Mg2+ S2-

Using solubility rules Use to determine whether a written reaction will actually happen or not by providing the state descriptors Precipitates are usually a driving force for double displacement reactions between ionic compounds. If no product is a solid, the reaction does not happen. Ex: CaCl2 + K2SO4  2 KCl + CaSO4 Ex: 2 LiNO3 + Pb(C2H3O2)2  2 LiC2H3O2 + Pb(NO3)2 Ex: (NH4)2O + AlCl3  NH4Cl + Al2O3 Ex: BaI2 + Na2S  2 NaI + BaS Soluble Insoluble (Precipitates) Li+, Na+, K+, NH4+ (primary rule) NO3-, C2H3O2-, ClO3- Cl-, Br-, I- Ag+, Hg22+ , Pb2+ SO42- Ba2+, Ca2+, Sr2+ CO32-, O2-, PO43- OH- Ba2+, Ca2+, Sr2+, Mg2+ S2-

Net Ionic Equations For precipitation reactions, there are three ways to represent the equation. Molecular equation Complete ionic equation Net ionic equation Ions not participating in the net ionic equation are called spectator ions Ex: 2 KI(aq) + Pb(NO3)2  PbI2 (s) + 2 KNO3 (aq)

2) Formation of water: Acids and Bases Acids react with bases to form water and an ionic salt. Formation of water is a driving force. Recall acids are molecular compounds that dissociate to form ions. 6 acids dissociate completely and are called strong acids. (memory item) HCl HBr HI HNO3 H2SO4 HClO4 All other acids are weak acids that do not split into ions. Hydroxides of alkali and alkaline earth metals are strong bases. Ex: HC2H3O2 (aq) + NaOH(aq)  H2O (l) + NaC2H3O2 (aq)

3) Formation of a gas If a gas is produced, it will the driving force. Acid base reactions, decomposition reactions, and combustions often form gases. Common gases are CO2, NO2, SO2, NH3, H2S, H2, O2, N2, F2, Cl2 If a product is a gas, then gas formation is a driving force. Ex: K2CO3 (s)  K2O (s) + CO2(g)

4) Transfer of electrons: Oxidation-Reduction How to identify a redox reaction Is there an atom that is an element on one side and in a compound on the other side? (Single Replacement reaction) Is there an element that has a different charge ion on both sides? (Many synthesis and decomposition reactions. Also combustion.) Transfer of electrons is a driving force. Elements are driven to complete octets. Note: All combustion reactions are driven by electron transfer.

Activity Series For single replacement reactions, the determining factor is the place of the two metals in the activity series. In general, a metal can displace any of the metals which are lower in the activity series: Ex: Cu + AgNO3  Cu(NO3)2 + Ag Ex: Cu + Fe(NO3)3  Cu (NO3)2 + Fe Ex: Zn + Fe(NO3)3  Zn (NO3)2 + Fe

Reactivity Series for Halogens In general, a halogen can displace any of the halogens which are lower in the activity series for halogens. Notice that the activity series of halogens is just their order within the periodic table. Ex: F2 + 2 NaBr  2 NaF + Br2 Ex: Br2 + 2 NaCl  2 NaBr + Cl2

Exit Slip - Homework Exit Slip: Determine the net ionic equation for: Pb(NO3)2 (aq) + 2 NaOH (aq)  Pb(OH)2 (s) + 2 NaNO3 (aq) What’s Due? (Pending assignments to complete.) Start the Driving Forces Worksheet (Page 1 and top of page 2) What’s Next? (How to prepare for the next day) Read p473, p286-288, p548-549, p280-282