chapter 8 chemical reactions

Chapter 8 Chemical Reactions

Balancing Equations &Types of Chemical Reactions

GCC CHM 130

8.1 Chemical Reactions

Is this a chemical or physical change?

Is this a chemical or physical change?

What are four signs a chemical reaction may have occurred?

1 A precipitate forms

2 A gas forms w/o heating

3 Energy is released or absorbed

4 A permanent color change

Phys

Chem

Review

• What is the difference between a chemical change (reaction) and a physical change?

A physical change does NOT change the molecule – no bonds are broken, often just the state of matter changes. A chemical reaction DOES change the molecule into a different one.

• Reactants Products

• Balanced – same atoms on both sides

• Remember to include physical states(s) = solid(l) = liquid(g) = gas(aq) = aqueous solution (dissolved in water)

8.2 Chemical Reactions

8.3 Remember

• Which elements are solid, liquid, gas• Which are diatomic• Matter can not be created or destroyed so

reactions must be balanced• Subscripts tell how many atoms in that

molecule H2O

• Coefficients tell how many molecules 3 H2O

Write the balanced chemical reaction

A = Blue B = Red

3 A2 + B2 2 A3B

N2 (g) + H2 (g) NH3 (g)

H2 (g) + Br2 (l) HBr (g)

CO (g) + O2 (g) CO2 (g)

Draw and Balance These

N2 (g) + 3 H2 (g) 2 NH3 (g)

H2 (g) + Br2 (l) 2 HBr (g)

2 CO (g) + O2 (g) 2 CO2 (g)

How to Balance a Rxn

1. Write the unbalanced chemical reaction

with proper formulas first

Ex: Sodium reacts with chlorine to produce solid sodium chloride.

Na (s) + Cl2 (g) NaCl (s)

Why Cl2 not just Cl??? Cl is diatomic !!!

If Cl is diatomic, why not NaCl2?

Diatomic is only when elements are alone, does not apply to compounds.

2. Now change the coefficients never the subscripts till balanced.

Count polyatomic ions as a group, don’t count the atoms.

Answer:

2 Na (s) + Cl2 (g) 2NaCl (s)

Why can’t we change the subscripts?

Write the reaction:Hydrogen reacts with oxygen to form water vapor.

H2 (g) + O2 (g) H2O (g)

Now balance and use the lowest possible numbers. (Like reducing a number)

You FIRST write the reaction with PROPER FORMULAS, once that is

done you can NOT change the subscripts. Then you can balance

by adding coefficients.

Writing a reaction from words

• Write then balance the reaction of phosphorus being heated with oxygen gas to make solid diphosphorus pentaoxide.

4 P (s) + 5 O2(g) 2 P2O5(s)

There are many in the end of chapter problems like this to practice.

P (s) + O2(g) P2O5(s)

Hard Practice Prob – do at homeI’ll give answers next class (remind me)

• Write then balance this reaction: aqueous nickel(III) sulfate plus lead(II) nitrate produces nickel(III) nitrate and solid lead(II) sulfate

Ni2(SO4)3 (aq) + Pb(NO3)2 (aq) Ni(NO3)3 (aq) + PbSO4 (s)

Ni2(SO4)3 (aq) + 3 Pb(NO3)2 (aq) 2 Ni(NO3)3 (aq) + 3 PbSO4 (s)

8.4 Types of Chemical Reactions

8.5 Combination Reactions: 2 reactants form one product

8.6 Decomposition: one reactant forms 2 or more products

Combustion: burning with O2 to form carbon dioxide and steam

A + X AX

AX A + X

CxHy + O2(g) CO2 (g) + H2O (g)

AX (aq) + BY (aq) AY (aq) + BX (s)

HA(aq) + MOH(aq) H2O (l) + MA(aq)

8.10 Double Replacement Reactions: switch partners

8.11 Neutralization Reactions: acid + base form water and salt

8.8 Single Replacement: metal A becomes part of an ionic cmpdA + BX AX + B

8.5 Combination Reactions

8.6 Decomposition Reactions

2 P (s) + 2 O2 (g) → P2O4 (g)

2 Fe2O3 (s) → 4 Fe (s) + 3 O2 (g)

Balance: P (s) + O2 (g) → P2O4 (g)

Balance: Fe2O3 (s) → Fe (s) + O2 (g)

Combustion Reactions

Write then balance the combustion of Propane gas,

C3H8

C3H8 (g) + O2 (g) CO2 (g) + H2O (g)

C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)

Combustion Reactions

We are only doing simple hydrocarbon (CxHy) combusion reactions. So…

Products are always CO2(g) + H2O(g)And

O2(g) is always a reactant

You should be able to predict the products for these !!!

8.7 Activity Series• Given to you on Periodic Table• Most active WANTS to be cation (+ charge) in

compound with a buddy (social)• Least active WANTS to be alone as neutral

element metal with zero charge (loner)

8.9 Solubility RulesSolubility Rules

Generally soluble compounds with:1.Li+, Na+, K+, NH4

+ (ALWAYS!)2.C2H3O2

-, 3.NO3

-

4.Halide ions (X), Cl-, Br-, I-

- BUT AgX, Hg2X2, HgX, PbX2 insoluble4.SO4

2-

- BUT SrSO4, BaSO4, , PbSO4 are all insoluble

Generally insoluble compounds with:6.CO3

2-

7.CrO42-

8.PO43-

9.S2-

- BUT CaS, SrS, BaS soluble10.OH-

- BUT Ca(OH)2, Sr(OH)2, and Ba(OH)2 soluble

Soluble means dissolves in water. NaCl(aq) which is Na+ and Cl- ions in water

Insoluble means does not or very little dissolves in water.

AgCl(s)

Drawings!

Draw these chemicals in beakers of water.

LiNO3 MgS Ca(OH)2 KI BaCO3

Soluble is (aq), insoluble is (s)Write (aq) or (s) by each.

Al(OH)3 Ca(NO3)2

K2S Li3PO4

Ba(C2H3O2)2

Sr(OH)2 (NH4)2CO3

PbI2 CuS

(aq)

(aq)

(aq)

(aq)

(aq)

(aq)

(s)

(s)

(s)

Now for practice let’s NAME these compounds!

Electrolytes• Electrolytes are solutions that contain ions• Strong electrolytes are good conductors, ionic

compounds that are soluble (completely dissolves into ions) are these. You will learn later that strong acids and bases are strong electrolytes.

• Weak electrolytes are weak conductors, ionic compounds that are insoluble are these. Insoluble = only a few dissolve into ions. You will learn later that weak acids and bases are weak electrolytes.

• Non-electrolytes are solutions that do not conduct at all, zero ions. Covalent chemicals are often non-electrolytes.

• http://www.youtube.com/watch?v=1XWnovm6JLs&feature=related

8.8 Single Replacement Reactions

Zn(NO3)2 (aq) + Na (s) → ?

1. Look at the two metals or H, which is more active?2. Most active wants to be in compound, if it already is

then No Reaction (NR), if not switch partners.3. Write the correct product formulas – the elemental

state is always charge 04. Write the states for the products. (s, l, g, aq)5. Last is balance.

Zn(NO3)2 (aq) + 2 Na (s) → 2 NaNO3 (aq) + Zn (s)

Why not Na(NO3)2???Na is +1 and NO3 is –1 so they already balance out, don’t need 2

Solid Metal + Acid

If a metal is more active than H, then H2 gas produced. (You must write the products 1st, then the states, then balance last)

Al (s) + HCl (aq) ?

2 Al (s) + 6 HCl (aq) 2 AlCl3 (aq) + 3 H2 (g)

Al (s) + HCl (aq) AlCl3 (aq) + H2 (g)

Al (s) + HCl (aq) AlCl3 (?) + H2 (?)

Active Metalshttp://video.google.com/videoplay?docid=-3103610687149839311#

http://www.youtube.com/watch?v=OFG4Yr7lQzw

Active Metals Series: Li > K > Ba > Sr > Ca > Na

The six active metals will react with waterto produce hydrogen gas and the metal hydroxide.

M (s) + H2O (l) → H2 (g) + MOH

1. Cu (s) + H2O(l)

2. Ba (s) + H2O(l)

NR

H2 (g) + Ba(OH)2 (aq)

Write the reaction and balance (You must write the products 1st)

2

17.1 Oxidation and Reduction

• Single Replacement reactions are a type of REDOX reaction where oxidation and reduction occur. (Note you can’t have one without the other)

Oxidation Numbers• Ox # = fancy name for charge• All elements in natural state = 0• When in a compound, charge is + for metals

and – for nonmetals depending on how many electrons lost or gained

• Variable charge metals range from +1 to +9 in rare cases.

Nomenclature worksheet has this info online Review CHARGES!!!

http://web.gccaz.edu/~ksmith8/rev130.htm

17.2 Oxidation• Losing electrons, charge goes ______________

• Cu(s) Cu2+ (aq) + 2 e-

• Solid Cu is oxidized (OX = UP)

• What is oxidized = reducing agent

• What elements like to lose electrons?

UP

metals

Reduction• Gaining electrons, charge goes ______________

• S (s) + 2 e- S2- (aq)

• Solid sulfur is reduced

• What is reduced = oxidizing agent

• What elements like to gain electrons?

DOWN

nonmetals

Redox Reactions• Must have one chemical oxidized AND another

reduced. Can’t have one w/o the other.• What is oxidized and reduced are always reactants,

the products are the result of the redox. • So if asked “what is ox or red?”, answer is reactant

chemicals. • When you answer, answer the whole compound, not

just the element that changed charges. • You have to figure out the charges!!!

Easy example

Cu+2 (aq) + Fe(s) Cu(s) + Fe+2(aq)

Cu went from +2 to 0 so charge down = reducedFe went from 0 to +2 so charge up = oxidized

What is oxidized?What is reduced?What is oxidizing agent?What is reducing agent?

Fe (s)Cu+2 (aq)Cu+2(aq)Fe(s)

What is oxidized, reduced, ox agent, and red agent???

• Co charge went from +3 to 0• Pt charge went from 0 to +3• So Co(NO3)3 is reduced (cobalt(III) nitrate)

• Pt(s) is oxidized• Co(NO3)3 is oxidizing agent

• Pt(s) is reducing agent

Co(NO3)3 (aq) + Pt (s) Pt (NO3)3 (aq) + Co(s)

What is oxidized, reduced? What is the ox agent, red agent?

Ca(s) + NiCl2 (aq) CaCl2(aq) + Ni(s)

Ox = solid Ca NOT Ca2+ or CaCl2 Red = NiCl2 (aq) for fun what is the name?Ox Agent = NiCl2 (aq)Red Agent = Ca(s)

(nickel(II) chloride)

Do the redox practice problems in the online notes !!! AND there is a worksheet online for redox.

AX (aq) + BY (aq) → AY (s) + BX (aq)

8.10 Double Replacement Reactions Precipitation is a type of DR Rxn and a solid forms

1. Ba(NO3)2 (aq) + MgSO4 (aq) → BaSO4 + Mg(NO3)2

2. Pb(NO3)2 (aq) + KI (aq) → PbI2 + KNO3

3. BaCl2 (aq) + AgNO3 (aq) → Ba(NO3)2 + AgCl

Identify the solid then balance.

2

2 2

2

(aq)

(aq)

(aq)

(s)

(s)

(s)

HA + MOH → H2O + MA

8.11 Neutralization ReactionsAnother type of DR Reaction

Acid Base

Write the products, the states, and THEN balance.

Products are usually water and ionic compound.

HCl (aq) + Ba(OH)2 (aq)

H3PO4 (aq) + Ca(OH)2 (aq)

2 H2O (l) + BaCl2 (aq)

2

2

Ca3(PO4)2 (s) + 6 H2O (l)3

Summary• Know how to use solubility rules and draw ionic

compounds in beakers of water• Recognize strong vs weak electrolytes• Recognize and balance

– Combination – Decomposition– Double displacement - precipitation

• Recognize, write products, and balance– Single displacement– Acid base neutralization– Combustion

• Identify what is oxidized, reduced and the agents in a redox reaction

You REALLY should do the worksheets for chapter 8 on the

Worksheet website

http://web.gccaz.edu/~ksmith8/rev130.htm

Self Tests

• Page 230 Ch. 8 Try 1-5, 7-9, 11-16• Page 510 Ch. 17 Try 1-2• Answers in Appendix J