Chemistry SM-1131Week 10 Lesson 1

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Test Friday 5,6,7!• Chemical Reactions• Types of Chemical Reactions• Balancing Chemical Reactions• New Material: Double Displacement, acid base,

spectator ions, solubility rules, precipitation reactions• Take Home Quiz due Friday!

Consequences• “When you play with the big boys you’re going

to get hurt.” • “There are consequences to your actions.” Sheryl A. Blair

Chemical Reactions• A chemical reaction is a rearrangement of

atoms.• Reactants Products

Evidence of a Chemical Reaction

• Heat and Light• Formation of solids• Gas emitting• Changing colors• Change in temperature

Some quick vocab• (g) means the substance is a gas• (l) means the substance is a liquid• (s) means the substance is a solid• (aq) means the substance is aqueous• Aqueous means dissolved in water.

Rules about Chemical Equations

• Remember that law of conservation of mass?• Matter can neither be created nor destroyed.• We’ll start with skeleton equations• We’ll alter it to make a balanced equation.

Counting molecules and atoms

• 2H2O

• 4Mg(NO3)2

• The 2 and the 4 are called coefficients, just like 5X in math where the 5 is the coefficient.

Types of Chemical Reactions

• There are 5 main types of reactions• Combination aka synthesis• Decomposition• Combustion• Single displacement• Double displacement• (Acid Base, gas evolution, precipitation,

oxidation and reduction aka redox)

Combination Reactions• 2 things come together to make 1 thing.• Carbon and Hydrogen react to form the

compound methane.• C + H2 CH4 is the skeleton equation

• C + 2H2 CH4 is the balanced equation

Combination Reaction 2• Mg and oxygen react at high temperature

what is formed?• Mg + O2 MgO

• O2 is diatomic when written into reactions (HINClBrOF)

• (How’d I know MgO, well 4 steps: symbols, charges, switcheroo, reduce)

• To balance it…

Balancing Chemical Reactions

• ___ Mg + ___ O2 ___MgO• 1- for all ionic compounds correctly establish

their formula• 2-List all elements in the rxn under the arrow• 3-Count the number of atoms of each type on

both sides of the equation• 4-Starting with metals change the coefficients

until both sides are balanced. DO NOT CHANGE CHEMICAL FORMULAS.

Balancing Chemical Reactions

• ___ Mg + ___ O2 ___MgO ___Mg___ ___O___• ___ Mg + ___ O2 ___MgO 1 Mg 1 2 O 1 NOT BALANCED• ___ Mg + ___ O2 _2_MgO 1 Mg 2 2 O 2 NOT BALANCED• _2_ Mg + ___ O2 _2_MgO 2 Mg 2 2 O 2 BALANCED

More examples

• N2 + 3H2 2NH3

• 2Al + 3F2 2AlF3

• P4 + 5O2 P4O10

• SO3 + H2O H2SO4

Decomposition• When things decompose they break down.

This reaction is where 1 molecule breaks down into several molecules.

• Iron(III) chloride decomposes at high temperature into it’s elements.

• FeCl3 Fe + Cl2

• Not balanced, again HINClBrOF

Electrolysis of water• Electrolysis is when you put a current through water. Water

turns into it’s elements. Write and balance the reaction.• ___H2O ___H2 + ___O2 _2H 2 _1O_2 • _2_H2O ___H2 + ___O2 _4H_2 _2O_2• _2_H2O _2_H2 + ___O2 _4H_4 _2O_2

More examples of Decomposition

• CaCO3 CaO + CO2

• 2 HgO 2 Hg + O2

• 2 KClO3 2KCl + 3O2

Combustion Reactions• Combustion means burning and fire. What

two things does fire require? O2 and something to burn. We normally burn hydrocarbons (Hydro=H, Carbon = C therefore stuff made up of H and C).

• The products are always CO2 and H2O.• Methane and Oxygen burn write the equation.• ___CH4+ ___O2 ___ CO2 + ___H2O

Balance a combustion

• ___CH4+ ___O2 ___ CO2 + ___H2O __C __ __H __ __O __ (it comes from 2 places)

Balance this reaction now

Balanced Reaction

• _1_CH4+ _2_O2 _1_ CO2 + _2_H2O 1_C 1_ 4_H 4_ 4_O 4_ (it comes from 2 places)

Harder example

• C2H6 + O2 CO2 + H2O 2 C 1_ 6 H 2_ 2 O 3_• C2H6 + 3.5 O2 2 CO2 + 3 H2O 2 C 2_ 6 H 6_ 7 O 7_(no such thing as 0.5O2)

Double all the coefficients

• 2C2H6 + 7 O2 4 CO2 + 6 H2O 4 C 4_ 12 H 12_ 14 O 14_All combustion reactions will be just like one of

those two reaction.

Displacements• These are the 2 hardest to tell apart when

starting.• Single displacements typically have 1 lone

element on both sides of the reaction• Double displacements look like the biggest

reactions out there, and you’ll see that the two metals switch places

Single Displacement• Magnesium metal starts making hydrogen gas

when it’s dropped in aqueous hydrochloric acid. What’s the full reaction?

___Mg + ___HCl ___ H2+ __ ?

Single Displacement

• ___Mg + ___HCl ___ H2+ __ MgCl?• NO! 4 steps when writing ionic salts ALWAYS!

So, it’s MgCl2

• ___Mg + ___HCl ___ H2+ __ MgCl2

1 Mg 1_ 1 H 2_ 1 Cl 2____Mg + _2_HCl ___ H2+ __ MgCl2

Single Displacement

• ___Mg + _2_HCl ___ H2+ __ MgCl2

• Notice: Mg is elemental on the left side, and Hydrogen is elemental on the right side.

• The single lone element was displaced by a different lone element.

More Examples

• 3AgCl + Al AlCl3 +3 Ag

• 2Na + H2O H2 + 2NaOH

• Zn3N2 + 3Mg Mg3N2 + 3Zn

Double Displacementel double

• Silver nitrate and sodium chloride react to form silver chloride and sodium nitrate. Write and balance the reaction.

• KEY POINT: FIGURE OUT THE FORMULA FOR EACH INORGANIC PIECE AND DON’T MESS WITH THE FORMULA FOR THE REST OF THE TIME!

El Double

• AgNO3 + NaCl AgCl + NaNO3

• It’s already balanced.• The Ag and Na switched places.• That’s why it’s a double displacement.

El Double 2• Barium nitrate and potassium sulfate reaction

to form barium sulfate and potassium nitrate. Write and balance the equation.

Ba(NO3)2 + K2SO4 Ba(SO4) + KNO3

Ba _ K _ (NO3) _ (SO4) _

Acid Base• These are like double displacement reactions,

except one of the compounds is going to be an acid and the other will be an ionorganic salt

• Salt just means combination of a cation and anion in a solid form

• Hydrochloric acid and sodium hydroxide react together. Write the reaction.

ACID BASE• HCl + NaOH ____ + ____• The “metals” swithc places. So H and Na will

switch. Na will be with Cl, and H will be with OH

• HCl + NaOH NaCl + H2O

Acid Base• Phosphoric acid and sodium hydroxide are

stirred in a beaker together what products are made?

Acid Base

• H3PO4 + NaOH Na3PO4 + H2O = skeleton• Balance this

Solubility• Often times we perform a double

displacement reaction to actually collect one of the products. We can make certain compounds crash out of (precipitate) an aqueous solution because of how soluble some compounds are.

• We’ll take two soluble compounds, they will react, and they will typically make one soluble product and one insoluble product.

Na2SO4 and BaCl2

• Na2SO4 + BaCl2 NaCl + Ba(SO4) skeleton

• Balance this (if you make a compound Na2Cl2 you are wrong and bad! We don’t mess with formulas after they are set. We just change coefficients).

Solubility Rules• You did that reaction in lab! The BaSO4 was a

powder that crashed out of solution and you filtered it off! Why did it crash out? Because of solubility rules.

Solubility Rules• Any compound with Li, Na, K, or NH4 will always be

soluble• Any compound with NO3 or C2H3O2 will always be

soluble• Compounds with Cl, Br, I will be soluble except with

Ag, Hg or Pb• Compounds with SO4 will be soluble except with Sr,

Ba, Pb, or Ca• Compounds with CO3 and PO4 are insoluble unless

with Li, Na, K or NH4

Barium• Ok, so let’s take our barium and sulfate

reaction and try to figure out which are soluble pieces and which are not.

Solubility Rules with Sulfate lab

• Na2SO4(?) + BaCl2(?) NaCl(?) + Ba(SO4)(?)

• Compounds with Na are ?• Compounds with Cl are?• Compounds with Na are?• Compounds with Sulfate are? Except with?

Solubility

• Na2SO4(aq) + BaCl2(aq) NaCl(aq) + Ba(SO4)(s)

Dissolving• So, what happens when an inorganic

compounds dissolves (this is totally different than a molecular compound dissolving)?

• Water molecules act as crowbars that split molecules into pieces. The two pieces formed are the cations and the anions.

• When you see table salt it’s the compound NaCl. When you dissolve it in water it’s actually Na+ and Cl-.

Try some more

• Ag(NO3) Ag+ and NO3-

• Na2(SO4) 2Na+ and SO4-2

• H3PO4 3H+ and PO43-

• Na(OH) Na + and OH-

• Li3(PO4) 3Li+ and PO43-

Molecular Compounds• Molecular compounds don’t do that.• C6H6O6(s) C6H6O6(aq) no change occurs.

Spectator• Spectator ions- reactions have components

that aren’t that important to the overall effect. We can tell they aren’t that important because they appear on both sides of the chemical equation. They aren’t really participating, they are just hanging out. We call them spectator ions.

Net Ionic Equations• Net just means overall, so we’re trying to

figure out what’s the overall reaction.• Aluminum chloride and sodium phosphate

undergo a double displacement reaction. What precipitates and what’s the net ionic equation?

• AlCl3 + Na3PO4 AlPO4 + NaCl = skeleton

• AlCl3 + Na3PO4 AlPO4 + 3NaCl = balanced• AlCl3(aq) + Na3PO4(aq) AlPO4(s) + 3NaCl(aq) total eq

Total Ionic

• AlCl3(aq) + Na3PO4(aq) AlPO4(s) + 3NaCl(aq) total eq

Al+3(aq) + 3Cl-

(aq) + 3Na+(aq) + PO4

3-(aq) AlPO4(s) + 3Na+

(aq) + 3Cl-(aq)

• That’s the total ionic equation• Note the (s) thing is not in pieces. That’s

because only things that are (aq) are going to break up like that.

• To get the net ionic we have to cancel out the spectator ions from both sides.

NetAl+3

(aq) + 3Cl-(aq) + 3Na+

(aq) + PO43-

(aq) AlPO4(s) + 3Na+(aq) + 3Cl-

(aq)

3Cl-(aq) + 3Na+

(aq) appear on both sides of the equation. We’re going to cancel them out. If we do that it leaves us with the “Net Ionic Equation.”

• Al+3(aq) + PO4

3-(aq) AlPO4(s) is the net equation.

So steps?• 1-Inorganic formula writing for each inorganic

compound• 2-skeleton equation• 3-balanced equation• 4-total equation (add solubilities)• 5-Total ionic equation• 6-Cancel out spectator ions• 7-Net ionic equations

Chapter 7 Take Home Quiz 8pts

• 1-Berylium chloride and aluminum react together. What is the reaction type? Balance the chemical reaction.

• 2-Magnesium chloride and sodium phosphate undergo a double displacement reaction. Go through all the steps to show the net ionic equation.

• 3- When you cook with a propane grill you burn propane. Write the combustion rxn.

• 4- Sulfuric acid and magnesium hydroxide are spilled in a warehouse. What reaction type is this. Do all the steps to show the net ionic reaction.