Chemical Equation A representation of a chemical reaction: C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O reactants products

Chemical Equation C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O The equation is balanced. 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water

Molecular representation of a rxn

Molecular rep of a rxn

Which of the following correctly describes the balanced chemical equation given below? There may be more than one true statement. 4Al + 3O 2  2Al 2 O 3 I.For every 4 atoms of aluminum that react with 6 atoms of oxygen, 2 molecules of aluminum oxide are produced. II.For every 4 moles of aluminum that react with 3 moles of oxygen, 2 moles of aluminum oxide are produced. III.For every 4 grams of aluminum that react with 3 grams of oxygen, 2 grams of aluminum oxide are produced. Bam!

Rules for Balancing Reactions For each element, the number of atoms on the reactant side must equal the number of atoms on the product side. The subscripts cannot change. Only coefficients can be changed. The coefficients must be whole numbers. The coefficients must be simplified (divided down) as much as possible.

Which of the following correctly balance the chemical equation given below? There may be more than one correct balanced equation. CaO + C  CaC 2 + CO 2 I. CaO 2 + 3C  CaC 2 + CO 2 II.2CaO + 5C  2CaC 2 + CO 2 III.CaO + (2.5)C  CaC 2 + (0.5)CO 2 IV.4CaO + 10C  4CaC 2 + 2CO 2 Woot!

Which of the following statements are true concerning balanced chemical equations? There may be more than one true statement. I. The number of molecules is conserved. II. The coefficients tell you how much of each substance you have. III.Atoms are neither created nor destroyed. IV.The coefficients indicate the mass ratios of the substances used. V.The sum of the coefficients on the reactant side equals the sum of the coefficients on the product side. Huh?

1. CH 4 + O 2  CO 2 + H 2 O 2.SiO 2 + HF  SiF 4 + H 2 O 3.K + H 2 O  H 2 + KOH 4.C 2 H 6 + O 2  CO 2 + H 2 O 5.NH 3 + O 2  NO + H 2 O

1. H 2 SO 4 + Ca(OH) 2  CaSO 4 + H 2 O 2. Fe(CN) 3 + MgCl 2  FeCl 3 + Mg(CN) 2 3. K 3 PO 4 + H 2 O  H 3 PO 4 + KOH

Reaction Symbols (s) solid (l) liquid (g) gas (aq) aqueous = dissolved in water △ heat added (put over arrow)

Diatomic Molecules Remember which atoms make diatomic molecules: – H 2 and N 2, O 2, F 2 Cl 2 Br 2 I 2 -This is only when they are by themselves! -When other atoms are by themselves they don’t have any subscripts, for example iron is just Fe

Write the balance chemical equation for the following: 1)Hydrogen gas is ignited and burns, combining with oxygen to form water vapor. 2)Silver oxide is decomposed by strong heating into silver metal and oxygen gas.

3) Methanol (CH 3 OH) is synthesized from carbon monoxide gas and hydrogen gas. 4) If iron (III) oxide is heated strongly in a stream of carbon monoxide gas, it produces elemental iron and carbon dioxide gas.

Classifying Reactions 8 different types of reactions: 1. Precipitation reactions (aq) + (aq)  (s) + (aq) or (l) AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 2. Acid-base reactions --OH + H--  salt + H 2 O(l) NaOH(aq) + HCl(aq)  NaCl(aq) + H 2 O(l) 3. Oxidation-reduction reactions uncombined element on one side is combined on the other side Fe 2 O 3 (s) + Al(s)  Fe(l) + Al 2 O 3 (s)

4. Synthesis – one product N 2 + O 2  2NO 5. Decomposition – one reactant 2H 2 O  2H 2 + O 2 6. Combustion – O 2 is a reactant, O adds to each element If C and H, thenCO 2 + H 2 O are the products CH 4 + 2O 2  CO 2 + 2H 2 O

7. Double displacement – “doubles” on both sides AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 8. Single displacement – a “single” and a “double” on both sides Fe 2 O 3 (s) + Al(s)  Fe(l) + Al 2 O 3 (s) Another way to classify:

Precipitation Reactions Form a solid (s) on product side Must have only (aq) on reactant side The solid formed is NOT a strong electrolyte Pb(NO 3 ) 2(aq) + 2NaI (aq)  PbI 2(s) + 2NaNO 3(aq)

Is the product a solid????? –Will NOT be solid if: It contains a group I metal It contains NH 4 + It contains NO 3 -

Complete and balance the precipitation reactions: a) LiOH (aq) + MgS (aq)  b)PbCl 2(aq) + KBr (aq)  Identify the precipitate (solid) in each case!

Acid-Base Reactions Also called neutralization reactions Acids: they have H’s at the front, e.g. H 2 SO 4 –Their function is to give their H’s away Bases: they have OH’s at the end, e.g. Ba(OH) 2 –Their function is to take the acids H’s and combine with their OH’s to make H 2 O

Strong bases are always aq, never solid: –Group I with OH LiOH NaOH KOH RbOH CsOH -Certain Group II with OH -Ca(OH) 2 -Sr(OH) 2 -Ba(OH) 2

Strong acids -dissociate completely in water to produce H + ions. HCl  H + + Cl - H 2 SO 4  2H + + SO 4 2- Strong bases - dissociate completely in water to produce OH  ions. NaOH  Na + + OH - Ba(OH) 2  Ba OH - Equations that show the dissociation:

Acid-Base Reactions Always produce water and salt Salt = metal from base and leftovers from acid HNO 3(aq) + KOH (aq)  H 2 SO 4(aq) + LiOH (aq)  H 3 PO 4(aq) + Ca(OH) 2(aq) 

QUESTION

ANSWER

Give the acid base reaction that will produce the following salts: a)K 2 SO 4 b) CsNO 3

Sr(OH) 2 + H 3 PO 4 

Redox Reactions Oxidation-reduction (redox) –The oxidation number (charge) changes from reactant side to product side –Is a transfer of electrons –Element is alone on one side, but combined with other element(s) on the other side 2Mg + O 2  2MgO H 2 O (l)  H 2(g) + O 2(g)

QUESTION

ANSWER precipitation, redox, acid-base

3 more Reaction Types Synthesis – one product N 2 + O 2  2NO Decomposition – one reactant 2H 2 O  2H 2 + O 2 Combustion – O 2 is a reactant, CO 2 + H 2 O are the products CH 4 + 2O 2  CO 2 + 2H 2 O

–Double displacement AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) –Single displacement Fe 2 O 3 (s) + Al(s)  Fe(l) + Al 2 O 3 (s) Another way to classify:

1. CH 4 + O 2  CO 2 + H 2 O 2.SiO 2 + HF  SiF 4 + H 2 O 3.K + H 2 O  H 2 + KOH 4.Fe + O 2  Fe 2 O 3 5.NH 3 + O 2  NO + H 2 O

1. H 2 SO 4 + Ca(OH) 2  CaSO 4 + H 2 O 2. Fe(CN) 3 + MgCl 2  FeCl 3 + Mg(CN) 2 3. K 3 PO 4 + H 2 O  H 3 PO 4 + KOH 4.CaCO 3  CaO + CO 2

Electrolytes Strong – break up into + and – in water NaCl  Na + + Cl - Weak – only a few molecules break up in water vinegar solution Non - no molecules break up in water sugar solution

Strong Electrolytes Compounds containing a group 1 metal Compounds containing NH 4 + Compounds containing NO 3 - Strong acids Strong bases

The 7 Strong Acids HCl HBr HI HNO 3 H 2 SO 4 HClO 4 HClO 3

The 8 Strong Bases LiOH NaOH KOH RbOH CsOH Ba(OH) 2 Sr(OH) 2 Ca(OH) 2

Describing Reactions in Solution 1.Molecular equation (reactants and products as compounds) AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 2.Complete ionic equation (all strong electrolytes shown as ions) Ag + + NO 3  + Na + + Cl   AgCl(s) + Na + + NO 3 

Describing Reactions in Solution (continued) 3.Net ionic equation (show only components that actually react) Ag + + Cl   AgCl(s) Na + and NO 3  are spectator ions.

Pb(NO 3 ) 2(aq) + H 2 SO 4(aq)  PbSO 4(s) + HNO 3(aq) Write the balanced net ionic equation for the following reaction:

Give the molecular equation for Ni(NO 3 ) 2 + NaOH 

Give the net ionic equation for Ni(NO 3 ) 2 + NaOH 

Give the complete ionic equation for Ni(NO 3 ) 2 + NaOH 

What were the spectator ions in that equation?