Chapter 11 Chemical Reactions

Recognizing Chemical Rxns (1) When a sub undergoes a chem change, it takes part in a chem rxn. After it reacts, it no longer has the same chem identity.

Recognizing Chemical Rxns (2) A sub can undergo a chem change and become a different sub. chem rxns occur around you (e.g. rusting, bleaching) and inside your bodies (e.g. digestion, respiration) all the time.

Evidences of chem Rxn Many important clues indicate when chem rxns occur. Light given out Heat given out or absorbed Sound come out Change color

Evidences of chem Rxn (5) Precipitate form (6) Smoke come out (7) Bubbles (gas) formed (8) Explosion

Evidences of chemical Changes

Writing Chemical Eqns To describe any changes that take place recognize what sub react and what sub form.

Writing Chemical Eqns (1) Reactant A sub that undergoes a rxn. Product The new sub(s) formed. Reactant(s) product(s) A + B C + D

Writing Chemical Eqns (2) e.g. a familiar chem rxn involves the rxn between Fe and O2 (reactants) that produces iron(III) oxide---- rust (product). Iron + oxygen → iron (III) oxide Translate into skeleton eqn by substituting with symbols and formulas. Fe +

Word Eqns (1) Using words to describe a rxn all the reactants and products, with an arrow ‘ → ’ placed between them to represent change. Reactants are placed to the left of the →, and products are placed to the right.

Word Eqns (2) ‘+’ signs are used to separate reactants and also to separate products. Vinegar +baking soda sodium acetate + water+ carbon dioxide Write the word eqn for ‘rusting’ of iron. Iron +

Word Eqns (3) Vinegar and baking soda are common names. The cpd in vinegar that is involved in the rxn is acetic acid, and baking soda is NaHCO3. Acetic acid + sodium hydrogen carbonate → sodium acetate + water + carbon dioxide

Chemical Eqns (1) To convert Word Eqns into chem eqns Substitute the names of cpds and elements with chem formulas .

Chemical Eqns (2) CH3COOH + NaHCO3 CH3COONa + H2O + CO2 Baking soda/ sodium hydrogen carbonate Vinegar/ Acetic acid

Writing Chem Eqns Potassium + chlorine potassium chloride K + Cl2 KCl

Writing Chem Eqns K + Cl2 → KCl

Writing Chem Eqns Aluminum + oxygen → aluminum oxide → Write the skeleton eqn →

Writing Chem Eqns Al + O2 → Al2O3

Writing Chem Eqns Sodium hydroxide + hydrochloric acid→ sodium chloride + water →

Writing Chem Eqns NaOH + HCl → NaCl + H2O

Writing Chem eqns Magnesium hydroxide + sulfuric acid → magnesium sulfate + dihydrogen monoxide →

Writing Chem eqns Mg(OH)2 + H2SO4 → MgSO4 + H2O

Writing Chem eqns FeCl3 + NaOH → Fe(OH)3+ NaCl Iron (III) chloride + sodium hydroxide → iron (III) hydroxide + sodium chloride FeCl3 + NaOH → Fe(OH)3+ NaCl

Writing Chem eqns Carbon disulfide + chlorine → carbon tetrachloride + disulfur dichloride CS2 + Cl2 → CCl4+ S2Cl2

Writing Chem eqns Sodium hydrogen carbonate → Sodium carbonate + carbon dioxide + water NaHCO3 → Na2CO3 + CO2 + H2O

Writing Chem eqns Sodium hydroxide+ carbon dioxide → Sodium carbonate + dihydrogen monoxide NaOH + CO2 → Na2CO3 + H2O

Chemical Eqns (3) How to indicate the bubbles during this rxn are CO2? How to indicate that precipitate formed at the bottom of a test tube?

Chemical Eqns (5) CH3COOH(aq)+NaHCO3(s) →CH3COONa(aq)+H2O (l) + CO2 (g)

Chem Eqns (5) CH3COOH(aq)+NaHCO3(s) CH3COONa(aq) +H2O(l) +CO2(g)

Energy and Chem Eqns (1) Noticeable amts of energy are often released or absorbed during a chem rxn. If energy is absorbed → endothermic rxn.

Energy and Chem Eqns (2) e.g. the eqn for the rxn in which water breaks down into hydrogen and oxygen shows that energy must be added to the rxn.

Energy and Chem Eqns (3) Rxns that release heat energy→exothermic rxns.

Energy and Chem Eqns (4) a rxn that produces energy

Energy and Chem Eqns (5) The word energy is not always written in the eqn. It is used only if it is important to know whether energy is released or absorbed.

Total mass reactant(s) = total mass product(s) Balancing Chem Eqns (1) Law of conservation of mass Matter is neither created nor destroyed during a chem rxn. Total mass reactant(s) = total mass product(s)

Balancing Chem Eqns (2) In a chem rxn: Atoms don’t change; they just rearrange. breaking of bonds of reactants → rearrangement of atoms→ new bonds (in products) # and kinds of atoms in (reactants) = those in the products. Law of conservation of atoms

Balancing Chem Eqns (3) For a chem eqn to accurately represent a rxn, the same # of each kind of atom must be on the left side of the → as are on the right side. ■If an eqn follows the law of conservation of atoms → balanced.

Balancing Chem Eqns (4) e.g. consider the eqn that represents breaking down carbonic acid into water and CO2.

Balancing Chem Eqns (6) Examine the eqn for the formn of sodium carbonate and water from the rxn between sodium hydroxide and carbon dioxide.

Balancing Chem Eqns (7) 1 C atom is on each side of the arrow, but the Na, O, and H atoms are not balanced.

Balancing Chem Eqns (8) To indicate more than 1 unit taking part or being formed in a rxn, a # called a coefficient is placed in front of it to indicate how many units are involved. a coefficient of 2 in front of the NaOH formula

Balancing Chemical Eqns (9) 2 Na atoms are on each side. How many O atoms are on each side? 4 on each side. How about H atoms? 2 on each side. Because 1 C atom is still on each side, the entire eqn is balanced;

Balancing an Eqn The balanced eqn tells us that when NaOH and CO2 react, 2 units of NaOH react with each molecule of CO2 to form 1 unit of NaCO3 and 1 molecule of H2O.

Major Classes of Rxns (1) 5 Major Categories 1. Combination/Synthesis Rxns 2. Decomposition Rxns 3. Single replacement/displacement Rxns 4. Double replacement/displacement Rxns 5. Combustion Rxns

Reaction Types

Combination Rxn 1. Combination Rxn/ Synthesis Rxn 2 or more reactants (elements or cpds) combine →one single product (cpd). e.g. Fe + S → FeS elements cpd R + S → RS

A Synthesis Rxn When Fe rusts, Fe metal and O gas combine to form 1 new sub, iron(III) oxide. more than 1 reactant but only 1 product.

Combination Rxns Combination Reactions a chem change in which 2 or more subs react to form a single new sub.

Decomposition rxn 2. Decomposition Rxn 1 reactant (cpd) breaks down into 2 or more simpler subs (→ 2 or more products) cpd break down into individual elements or simpler cpds 2HgO(s) → 2Hg (l) + O2 (g) cpd Elements or cpds RS → R + S

Decomposition Rxns Decomposition Rxns a single cpd (reactant) breaks down into 2 or more simpler products.

Decomposition rxn 2HgO(s) → 2Hg (l) + O2 (g) 2 elements H2O2(l) → H2O(l) + O2(g) A cpd An element NH4NO3 (s) → N2O (g) + 2H2O (g) 2 cpds

Single-displacement rxn 3. Single-displacement/ Single replacement rxn: 1element takes the place of another in a cpd. The element can replace the 1st part of a cpd, or the last part of a cpd.

Single-Displacement rxn Fe nail is placed into an aq soln of copper(II) sulfate, the Fe displaces the copper ions in soln Cu metal forms on the nail. Fe(s) + CuSO4(aq) → FeSO4 (aq) +Cu (s) Metal (element) Ionic cpd Metal (element) Ionic cpd T + RS TS + R

Activity Series of Metals more reactive metals replace the less reactive ones. there is no rxn when …. Must refer to the Activity Series of Metals when predicting products in Single Replacement Rxns

Single-replacement Rxn Single-Replacement Rxns 1 element replaces a 2nd element in a cpd.

No Rxn e.g. Cu(s) + MgCl2 → no rxn (no single replacement rxn) because Cu is less reactive than Mg.

Double-replacement Rxn the +ve portions of 2 ionic cpds are interchanged. at least 1 of the products must be a ppt or water.

Double Displacement This solid is lead(II) iodide. Pb(NO3)2 (aq) + 2KI (aq) → PbI2(s) + 2KNO3(aq) Ionic cpds R+S- + T+U- → R+U-

Double-replacement rxn Double-Replacement Rxns involve an exchange of +ve ions between 2 cpds.

Combustion Rxns 5. A combustion rxn One reactant burns in O2 to form 1 or more oxides. e.g. Mg (s) + O2 (g) → MgO (s) oxides e.g. CH4 + O2 → CO2 + H2O CxHy + (x+y/4) O2 → xCO2 + (y/2) H2O

Combustion Rxns Combustion Reactions an element or a cpd reacts with O2, often producing energy in the form of heat and light.

Practice K + H2O → KOH + H2 Type of Rxn: _______________

Practice Li + Cl2 → Type of Rxn: _______________

Practice Zn + H2SO4 → Type of Rxn: ______________________

Practice Cl2 + NaBr → Type of Rxn: ____________________

Practice Cl2 + NaI → NaCl +

Practice NaOH + Fe(NO3)3 → Type of Rxn: _________________

Practice Type of Rxn: ______________________ Ba(NO3)2 + H3PO4 →

Practice CaBr2 + AgNO3 → Type of Rxn: ____________________

Practice FeS + HCl → Type of Rxn: _________________________

Practice NaOH + Fe(NO3)3 → Type of Rxn: ______________________

Practice KOH + H3PO4 → type of rxn : ___________________

Practice C2H6 + O2 → Type of Rxn: ________________________

CST problem 1 C3H8 + O2 → CO2 + H2O This chemical equation represents the combustion of propane. When correctly balanced, the coefficient for water is A 2. B 4. C 8. D 16.

CST problem 2 Which of the following is a balanced eqn for the combustion of ethanol (CH3CH2OH)? A CH3CH2OH + 3O2→ CO2 + 2H2O B CH3CH2OH + 3O2→ 2CO2 + 3H2O C CH3CH2OH + O2→ 2CO2 + 3H2O D CH3CH2OH + 2O2→ 3CO2 + 2H2O

The End

Question 1a Solid lithium reacts with chlorine gas to produce solid lithium chloride. Answer 1a

Question 1b Nitrogen gas reacts with oxygen gas to produce nitrogen dioxide gas. Answer 1b

Question 2 Write a balanced chem eqn for the following rxns, making sure coefficients are in their lowest possible ratio.

Writing Eqns for Single-Replacement Rxns Decomposition rxns that produce gases and heat are sometimes explosive, as the photo shows. Write a balanced eqn for the following decomposition rxn. H2O(l) electricity

Writing Eqns for Single-Replacement Rxns The photo shows the rxn between Zn(s) and H2SO4(aq). Write a balanced chemical eqn for each single-replacement rxn. The rxns take place in aq soln. Zn(s) + H2SO4(aq) → Cl2(aq) + NaBr(aq) →

Writing Chemical Ens A catalyst is a sub that speeds up the rxn but is not used up in the rxn. w/o Catalyst With Catalyst