Practice! How many atoms are in each of the following compounds? –H 2 SO 4 –Ca(NO 3 ) 2 –(NH 4 ) 3 PO 4 –C 6 H 12 O 6 –2 H 2 O –10 CO 2 7 atoms! 9 atoms! 20 atoms! 24 atoms! 6 atoms! 30 atoms!

CHEMICAL REACTIONS

Chemical reaction- the process by which the atoms of one or more substances are rearranged to form different substances.

Evidence of a chemical reaction: 1. Release of a gas Zinc is added to hydrochloric acid producing hydrogen gas and solid zinc chloride.

2. Color changes two liquids are mixed solid and a liquid mixed

3. Formation of a precipitate –a precipitate is a solid product formed by the reaction of two aqueous solutions. –It is abbreviated ppt. Aqueous sodium iodide and aqueous lead (II) nitrate produce solid lead (II) iodide and aqueous sodium nitrate.

4. Changes in heat and light –all reactions either absorb or release energy Sodium peroxide (yellow powder) and zinc powder (gray powder in the bowl) are combined Water is then squirted in & the mixture ignites

Writing Chemical Equations: reactants  products yield Na + Cl 2  NaCl EXAMPLE: From now on USE PENCIL!!

Writing Chemical Equations: Reactants—the starting substance(s). Products—the substance(s) formed during the reaction.

Possible symbols in chemical equations: + plus  yields (s) solid (l) liquid (g) gas (aq) aqueous  equilibrium N.R. no reaction  light or heat is added Catalyst (  & catalysts are written above the yield sign)

Examples: To what is the arrow pointing? H 2 O 2 (aq) H 2 O (l) + O 2 (g) MnO 2 CaCO 3 CaO (s) + CO 2 (g)  H 2 (g) + O 2 (g)  H 2 O (g)

Because of the principle of the conservation of mass, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 Conservation of Mass

Writing and Balancing Chemical Equations Example: Write the equation for the formation of sodium hydroxide and hydrogen, from the reaction of sodium with water. You must be able to write the symbol from the words and vice versa.

Write the equation for the formation of sodium hydroxide and hydrogen, from the reaction of sodium with water. 1.Write the formulas of all reactants to the left of the arrow and all products to the right of the arrow. Sodium + water Translate the equation and be sure the formulas are correct. Na + H 2 O  NaOH + H 2 sodium hydroxide + hydrogen

Write the equation for the formation of sodium hydroxide and hydrogen, from the reaction of sodium with water. 2.Once the formulas are correctly written, DO NOT change them. 2.Use coefficients (numbers in front of the formulas), to balance the equation. 2.DO NOT CHANGE THE SUBSCRIPTS! Coefficients are always whole numbers. _____Na + _____H 2 O  ____NaOH + _____H 2

Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound.The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules or formula units of the compound.The coefficient tells you about the quantity, or number, of molecules or formula units of the compound.

3.Begin balancing with an element that occurs only once on each side of the arrow. Ex: Na _____Na + _____H 2 O  ____NaOH + _____H 2 Na H O Na H O When you are finished, you should have equal numbers of each element on either side of the equation

4.To determine the number of atoms of a given element in one term of the equation, multiply the coefficient by the subscript of the element. Ex: In the previous equation (below), how many hydrogen atoms are there? 4 ____Na + _____H 2 O  ____NaOH + _____H 2 222

Take one element at a time, working left to right except for H and O. Save H for next-to- last, and O until last. IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units. (NH 4 ) 2 SO 4 (aq) + BaCl 2 (aq)  BaSO 4 (s) + NH 4 Cl (aq)

Balancing Equations ___ Al(s) + ___ Br 2 (l) ---> ___ Al 2 Br 6 (s) 23

Practice: Balance the equation for the formation of magnesium nitride from its elements. ____Mg + ____N 2  Mg 2+ N 3- Mg 3 N 2 3 ____Mg 3 N 2

Balance the reaction of sodium metal with chlorine gas to form sodium chloride. ____Na + ____Cl 2  NaCl Cl - Na + 22 ____NaCl

Ex:NH 3 + O 2  NO 2 + H 2 O H can be balanced by placing a 2 in front of NH 3 and a 3 in front of H 2 O. Then put a 2 in front of NO 2 for nitrogen to balance. _____NH 3 + _____O 2  ____NO 2 + ____H 2 O 232

Now all that is left to balance is the oxygen. There are 2 O on the reactant side and 7 on the product side. Our only source of oxygen is the O 2. Any whole number we place in front of the O 2 will result in an even number of atoms. The only way to balance the equation is double all the coefficients. _____NH 3 + _____O 2  ____NO 2 + ____H 2 O 232

Double all the coefficients, then add the 7 for the O 2. _____NH 3 + _____O 2  ____NO 2 + ____H 2 O 232 ____NH 3 + _____O 2  ____NO 2 + ____H 2 O 232 () 2 = _____NH 3 + _____O 2  ____NO 2 + ____H 2 O 4647

____H 2 + ____O 2  ____H 2 O ___NH 3 + ____O 2  ____NO 2 + ____H 2 O ___Ca + ___H 2 O  ___Ca(OH) 2 + ___H 2

__NH 4 Cl +__Ca(OH) 2  __NH 3 + __H 2 O+__CaCl 2 ___ZnO + ___HCl  ___ZnCl 2 + ___H 2 O ____K + _____F 2  _____KF ____C 2 H 4 + ____O 2  ____CO 2 + ____H 2 O

Types of Reactions There are five types of chemical reactions we will talk about: 1.Synthesis reactions 2.Decomposition reactions 3.Single displacement reactions 4.Double displacement reactions 5.Combustion reactions You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing Reactions Some steps for doing reactions 1.Identify the type of reaction 2.Predict the product(s) using the type of reaction as a model 3.Balance it Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O 2 as an element. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

Synthesis reaction (combination reaction)- the combination of two or more substances to form a compound Elem. or cmpd. + elem. or cmpd  cmpd. General form A + B  AB The product in a reaction will have different properties from either of the reactants that formed it.

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na (s) + Cl 2(g)  Solid Magnesium reacts with fluorine gas Mg (s) + F 2(g)  Aluminum metal reacts with fluorine gas Al (s) + F 2(g)  2 2NaCl (s) MgF 2(s) AlF 3(s) 2 3 2

Decomposition Reaction: is the breakdown of one substance into two or more other substances compound  two or more elements AB  A + B 2 H 2 O  2H 2 + O 2 2 HgO  2Hg + O 2

Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements. Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3  CO 2 + CaO Chlorates (ClO 3 - ) decompose to oxygen gas and a metal chloride Example: 2 Al(ClO 3 ) 3  2 AlCl O 2 There are other special cases, but we will not explore those in Chemistry I

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO 2(s)  Aluminum nitride decomposes AlN (s)  2 Pb (s) + O 2(g) Al (s) + N 2(g) 2

Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N 2(g) + O 2(g)  BaCO 3(s)  Co (s) + S (s)  NI 3(s)  Synthesis Decomposition Synthesis Decomposition 2 NO (g) N 2 (g) + I 2 (s) Co 2 S 3 (s) BaO (s) + CO 2 (g) (make Co be +3) Nitrogen monoxide

Single Replacement Reaction: One element replaces another element in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound  element + compound A + BC  AC + B When H 2 O splits into ions, it splits into H + and OH - (not H+ and O -2 !!)

Single Replacement Reactions Write and balance the following single replacement reaction equation: Zinc metal reacts with aqueous hydrochloric acid Zn (s) + HCl (aq)  ZnCl 2 + H 2(g) Note: Zinc replaces the hydrogen ion in the reaction 2

Single Replacement Reactions Sodium chloride solid reacts with fluorine gas NaCl (s) + F 2(g)  NaF (s) + Cl 2(g) Note that fluorine replaces chlorine in the compound Aluminum metal reacts with aqueous copper (II) nitrate Al (s) + Cu(NO 3 ) 2(aq)  Cu (s) + Al(NO 3 ) 3(aq)

To determine if a single replacement reaction will take place you must compare the activities of the elements involved. For metals, use the Activity Series. A metal will replace any metal below it on the activity series.

Activity Series of Metals and Halogens MetalsHalogens Deceasing activity LithiumFluorine PotassiumChlorine CalciumBromine SodiumIodine Magnesium Aluminum Zinc Chromium Iron Nickel Tin Lead HYDROGEN Copper Mercury Silver Platinum Gold Will Na replace Cr in a single replacement reaction? Yes!

Practice: ___I 2 + ___NaCl  ___AgNO 3 + ___Mg  ___KBr + ___F 2  ___Mg(NO 3 ) 2 + ____Cu  N.R. ___Mg(NO 3 ) 2 + ___Ag ___KF + ___Br 2 N.R Activity Series of Metals Lithium Potassium Barium Calcium Sodium Magnesium Aluminum Zinc Iron Cadmium Nickel Tin Lead Hydrogen (a nonmetal) Copper Mercury Silver Gold Platinum Metals from Li to Na will replace H from water and acids; metals from Mg to Pb will replace H from acids only. Decreasing Activity

Double Replacement Reaction: Two elements replace each other in compounds. occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound AB + CD  AD + CB MgCO 3 + 2HCl  MgCl 2 + H 2 CO 3 AgNO 3 + NaCl  AgCl + NaNO 3

Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO 3(aq) + NaCl (s)  AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq)  KNO 3(aq) + BaSO 4(s) 2

In order for double replacement reaction to take place, one of the products must be an insoluble solid (ppt), a gas, or water.

Negative IonPlusPositive IonForm a Compound Which is: Any negative ion+Alkali metal ions (Li +, Na +, K +, Rb +, Cs + ) Soluble Any negative ion+Ammonium ionSoluble Nitrate+Any positive ionSoluble Acetate+Any positive ion Ag + Soluble Not soluble Chloride, Bromide, or Iodide +Ag +, Pb 2+, Hg 2 2+, Cu + Any other positive ion Not soluble Soluble Sulfate+Ca 2+, Sr 2+, Ba 2+, Ra 2+, Ag +, Pb 2+ Any other positive ion Not soluble Soluble Sulfide+Alkali ions or Ammonium, Be, Mg, Ca, Sr, Ba, Ra, Any other positive ion Soluble Not soluble Hydroxide+Alkali ions or Ammonium Any other positive ion Soluble Not soluble Phosphate, Carbonate, or Sulfite +Alkali ions or Ammonium Any other positive ion Soluble Not soluble

CompoundPrecipitate Formed? BaSO 4 _______ Pb(NO 3 ) 2 _______ Ag 2 S_______ PbCl 2 _______ NH 4 Cl_______ Cr PO 4 _______ Yes No Yes No

__Na 2 SO 4 + __Ba(NO 3 ) 2  __NaOH + __Fe(NO 3 ) 3  __NaNO 3 + __Fe(OH) 3 __NaNO 3 + __BaSO Na + NO 3 - NaNO 3 Ba 2+ SO 4 2- BaSO 4 Na + NO 3 - NaNO 3 Fe 3+ OH - Fe(OH) 3

Practice Predict the products. Balance the equation 1.HCl (aq) + AgNO 3(aq)  2.CaCl 2(aq) + Na 3 PO 4(aq)  3.Pb(NO 3 ) 2(aq) + BaCl 2(aq)  4.FeCl 3(aq) + NaOH (aq)  5.H 2 SO 4(aq) + NaOH (aq)  6.KOH (aq) + CuSO 4(aq)  HNO 3(aq) + AgCl (s) Ca 3 (PO 4 ) 2(s) + NaCl (aq) 326 PbCl 2(s) + Ba(NO 3 ) 2(aq) Fe(OH) 3(s) + NaCl (aq) 33 H 2 O (l) + Na 2 SO 4(aq) 22 K 2 SO 4(aq) + Cu(OH) 2(s) 2

Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: –1) A Fuel (hydrocarbon) –2) Oxygen to burn it with –3) Something to ignite the reaction (spark)

General form for combustion of a hydrocarbon: C x H y + O 2  CO 2 + H 2 O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 )

Combustion Example C 5 H 12 + O 2  CO 2 + H 2 O Write the products and balance the following combustion reaction: C 10 H 22 + O 2  568 CO 2 + H 2 O

Examples ____C 3 H 8 + ____O 2  ____C 6 H 12 O 6 + ____O 2  ____CO 2 + ____H 2 O ____CO 2 + ____H 2 O

Mixed Practice State the type, predict the products, and balance the following reactions: 1.BaCl 2 + H 2 SO 4  2.C 6 H 12 + O 2  3.Zn + CuSO 4  4.Cs + Br 2  5.FeCO 3  BaSO 4 + HCl2 CO 2 + H 2 O 66 9 ZnSO 4 + Cu CsBr2 2 FeO + CO 2