Chapter 2 - Chemical Reactionspalmarin.weebly.com/uploads/2/3/0/7/23075168/... · Mr. Palmarin...

Chapter 2 - Chemical Reactions

Mr. Palmarin Chapter 2 - Chemical Reactions 1 / 47

Section 2.1 - Chemical Equations

Physical and Chemical Changes

Physical change: A substance changes its physical appearance, but notits composition. Example: All changes of state.

Chemical change: A substance is transformed into a chemically differentsubstance. Example: The burning of hydrogen in air.


Indicators of a Chemical Reaction

Chemical change:

Heat and/or light is given off

A new colour appears

A gas is produced

A solid precipitate (ppt) is formed

Watch: Nitric acid + copper Watch: Lead nitrate + potassium iodide


https://www.youtube.com/watch?v=uOa2v0Y0leU

https://www.youtube.com/watch?v=DITY2rXYU-I

Form of a Chemical Reaction

How can we describe a wide range of reactions?

Chemical Equations:

Reactants −−→ Products

We further separate both the reactants and the products by a plus sign:

Reactant 1 + Reactant 2 −−→ Product 1 + Product 2


Examples of word equations:

iron + oxygen −−→ iron(III) oxide

copper + silver nitrate −−→ silver + copper(II) nitrate

Examples of skeleton equations:

Zn + HCl −−→ H2 + ZnCl2

H2 + O2heat−−→ H2O or H2 + O2

4−−→ H2O

Note: The triangle above the reaction arrow indicates that heat wasadded to increase the rate of the reaction.


Examples: Write skeleton equations for the following reactions.

1) AgNO3 and NaCl react to form AgCl and NaNO3

This question is trivial. We simply will omit the words “and” and“react to form” and substitute them with the appropriate symbols.

AgNO3 + NaCl −−→ AgCl + NaNO3

2) Potassium sulphate reacts with barium nitrate to form potassiumnitrate and barium sulphate.

This question is identical to a question in Chapter 1. Essentially it is 4name to formula questions in one.

Step 1: Write down the appropriate charges that you will require.

K+ SO 2–4 + Ba2+ NO –

3 −−→ K+ NO –3 + Ba2+ SO 2–

4

Step 2: Now form the compounds using the charges (just like inChapter 1).

K2SO4 + Ba(NO3)2 −−→ KNO3 + BaSO4


Indicating the States of Reactants and Products

The physical state of each reactant and product is often added to theformulas in balanced equations. We use the symbols (g), (l), (s), and (aq)for gas, liquid, solid, and aqueous (water) solution.

Examples:

Fe(s) + O2(g) −−→ Fe2O3(s)

Zn(s) + 2 HCl(aq) −−→ H2(g) + ZnCl2(aq)

CH4(g) + 2 O2(g) −−→ CO2(g) + 2 H2O(g)


The Law of Conservation of Mass

In a chemical reaction, the total mass of the reactants is always equal tothe total mass of the products.

What does this imply?

In chemical reactions, the atoms of the reactants are simply rearranged to form

the products.


Section 2.2 - Balancing Chemical Equations

What’s incorrect with the chemical equation below?

Fe + Cl2 −−→ FeCl3

Problem! - The Law of Conservation of Mass states that the mass of thereactants equals the mass of the products.


We cannot change the subscripts of the formulas to fix this imbalance, asthis completely changes the compounds. Instead, we must change thenumbers of molecules rather than their formulas.

Fe + Fe + Cl2 + Cl2 + Cl2 −−→ FeCl3 + FeCl3

2Fe + 3Cl2 −−→ 2FeCl3


Steps to balancing chemical equations:

1 Balance metal elements

2 Balance non-metal elements excluding hydrogen and oxygen

3 Balance hydrogen

4 Balance oxygen

5 Reduce coefficients if possible

Tip! - If any polyatomics are present balance them as one unit. This onlyonly work if it occurs on both sides of the equation.


Balance the following equations:

1) Al + Br2 −−→ AlBr3

2) N2 + H2 −−→ NH3

3) N2H4 + O2 −−→ H2O + N2

4) Na + H2O −−→ NaOH + H2

5) Ca + HNO3 −−→ H2 + Ca(NO3)2

6) Fe(NO3)3 + (NH4)2CO3 −−→ Fe2(CO3)3 + NH4NO3


Solutions: [See Section 2.2 Video]

1) 2Al + 3Br2 −−→ 2AlBr3

2) N2 + 3H2 −−→ 2NH3

3) N2H4 + O2 −−→ 2H2O + N2

4) 2Na + 2H2O −−→ 2NaOH + H2

5) Ca + 2HNO3 −−→ H2 + Ca(NO3)2

6) 2Fe(NO3)3 + 3(NH4)2CO3 −−→ Fe2(CO3)3 + 6NH4NO3


Types of Chemical Reactions

We shall investigate five types of chemical reactions:

1 Combustion

2 Synthesis

3 Decomposition

4 Single Displacement

5 Double Displacement


Section 2.3 - Combustion Reactions

A combustion reaction is a reaction of the form:

hydrocarbon + oxygen +4−−→ carbon dioxide + water

CnH2n+2 + O2 −−→ CO2 + H2O

For example:

2 C4H10 + 13 O2 −−→ 8 CO2 + 10 H2O

Demonstration: 2 CH3OH + 3 O24−−→ 2 CO2 + 4 H2O

Watch: Combustion Reactions


https://www.youtube.com/watch?v=UygUcMkRy_c&ab_channel=MrLundScience

Balancing Combustion Reactions

For combustion reactions, we usually balance in this order:

1 Balance carbons

2 Balance hydrogens

3 Balance oxygens

Examples:

1) CH4 + O2 −−→ CO2 + H2O

2) C2H5OH + O2 −−→ CO2 + H2O

3) C2H6 + O2 −−→ CO2 + H2O

[See Section 2.3 Video]


Section 2.4 - Synthesis & Decomposition Reactions

Synthesis reactions involve the combination of smaller atoms and/ormolecules into larger molecules.

Simple synthesis reactions have the following general formula:

Watch: Synthesis of iron with sulfur


https://www.youtube.com/watch?v=A5H6DVe5FAI&ab_channel=ChemToddler

Simple (elements): A + B −−→ AB

Some complex synthesis reactions have the following general formulas:

Metal oxide + water −−→ Metal hydroxide (a base)

Ex: K2O + H2O −−→ 2 KOH

CaO + H2O −−→ Ca(OH)2

Non-metal oxide + water −−→ Non-metal hydride (an acid)

Steps:

1) Add one oxygen to the non-metal oxide2) This creates a new polyatomic ion. Reference its charge and placethe appropriate amount of hydrogens out front to balance the charges.

Ex: CO2 + H2O −−→ H2CO3


Examples: Complete and balance the following:

1) Na + Cl2 −−→ 2NaClThis is simple synthesis.

2) K + Cl2 −−→ 2KClAlso a simple synthesis.

3) Li2O + H2O −−→ 2LiOHThis is a complex synthesis - metal oxide + water. So we get ametal-hydroxide.

4) SO3 + H2O −−→ H2SO4

This is a complex synthesis - non-metal oxide + water. So you addan oxygen to get SO4. This is sulfate: SO 2–

4 so you must add 2hydrogens to cancel the charge.


Practice: Complete and balance the following: [See Section 2.4 Video]

1) Li + Br2 −−→

2) Mg + N2 −−→

3) SO2 + H2O −−→

4) BaO + H2O −−→


Decomposition Reactions

Decomposition reactions involve the splitting of a large molecule intoelements or smaller molecules.

Simple decomposition reactions have the following general formula:


Simple (elements): AB −−→ A + B

Some complex decomposition reactions have the following generalformulas:

Metallic carbonates: MCO3 −−→ MO + CO2

Metallic sulfates: MSO4 −−→ MO + SO3

Metallic hydroxides: MOH −−→ MO + H2O

Metallic chlorates: MClO3 −−→ MCl + O2

Acids: non-metal oxide + water

Demonstration: 2 H2O2 −−→ 2 H2O + O2

Watch: “Elephant Toothpaste”


https://www.youtube.com/watch?v=p1eG2y2mn54&ab_channel=ScienceBob


1) HgO −−→ ? 2HgO −−→ Hg + O2

This is simple decomposition. Simply separate the two elements.Notice how we get O2. This is because it is a homonuclear molecule;i.e. PS HOFBrINCl.

2) Ca(OH)2 −−→ ? Ca(OH)2 −−→ CaO + H2OThis is a complex decomposition. It is metallic hydroxide(MOH −−→ MO + H2O). Here M = Ca.

3) CaCO3 −−→ ? CaCO3 −−→ CaO + CO2

This is complex decomposition. It is a metallic carbonate(MCO3 −−→ MO + CO2).

4) ZnSO4 −−→ ? ZnSO4 −−→ ZnO + SO3

This is complex decomposition. It is a metallic sulfate(MSO4 −−→ MO + SO3).

5) KClO3 −−→ ? KClO3 −−→ KCl + O2

This is complex decomposition. It is a metallic chlorate(MClO3 −−→ MCl + O2).



1) AgCl −−→

2) MgCO3 −−→

3) Mg(OH)2 −−→

4) Sr(ClO3)2 −−→

5) FeSO4 −−→

6) H2CO3 −−→


Section 2.5 - Single & Double Displacement Reactions

Single Displacement Reactions

Single displacement reactions are chemical changes where one elementdisplaces or replaces another element from a compound. They have thefollowing general formula:

Note: Cations replace cations and anions replace anions!

Demonstration: CuCl2 + Al −−→

Watch: Single Displacement DemoMr. Palmarin Chapter 2 - Chemical Reactions 25 / 47

https://www.youtube.com/watch?v=1tqguW2QT2E&ab_channel=TanyaKatovich


1 Zn(s) + NiCl2(aq) −−→ ? −−→ ZnCl2 + Ni

Recall: Cations replace cations. Therefore, Zn will replace Ni. SinceZn takes a 2+ charge, it forms the compound ZnCl2.

2 Cu(s) + AgNO3(aq) −−→ ? −−→ Cu(NO3)2 + Ag

Recall: Cu replaces Ag. Now copper makes more than one charge.So when it forms a compound with NO –

3 , which ion takes it take?Notice how on our periodic table one ion coloured red for those thatmake more than one charge. This is there common charge. ForCu, 2+ is coloured red. Therefore, we have Cu2+ and NO –

3 forminga compound to give Cu(NO3)2.

3 2Na(s) + 2H2O(l) −−→ ? −−→ 2NaOH + H2

Cations replace cations. Na is a cation, but where’s the cation inH2O? Rewrite H2O as HOH. Now you can see that we have H+ andOH– . So Na will replace H. Then we get NaOH and since hydrogenis a homonuclear molecular, when it is alone, it becomes H2.



1 Zn(s) + CuCl2(aq) −−→

2 AuN(aq) + Ca(s) −−→

3 Ca(s) + H2O(l) −−→


Double Displacement Reactions

Double displacement reactions occur when elements in differentcompounds displace each other or exchange places. They have thefollowing general formula:

Note: Cations are always written first!

Demonstration: CuCl2 + Na3PO4 −−→

Watch: Double Displacement Demo


https://www.youtube.com/watch?v=3thjr51qIN4&ab_channel=MelanieHarlan


1 CaCl2(aq) + Na2SO4(aq) −−→ ? CaSO4 + 2NaCl

Cations replace cations (just like in single displacement). In fact, themethods are the same. This time, you must form two products. Ca isreplacing Na. So Ca2+ and SO2– form CaSO4, while you have Na+

and Cl– forming NaCl. Then balance both sides.

2 AgNO3(aq) + NaI(aq) −−→ ? AgI + NaNO3

Same as the above example. Ag replaces Na. Form the newcompounds and balance.



1 MgSO4(aq) + NaOH(aq) −−→

2 (NH4)2SO4(aq) + KOH(aq) −−→


Example:1 Classify each of the following reactions as a combustion, synthesis,

decomposition, single or double displacement reaction.2 Balance the chemical equation.

1) 8Mg + S8 −−→ 8MgSOne product always implies synthesis.

2) 2NaN3 −−→ 2Na + 3N2

One reactant always implies decomposition.

3) 2AgNO3 + Ni −−→ Ni(NO3)2 + 2AgTwo products with one product being an element always impliessingle displacement.

4) 2C2H6 + 5O2 −−→ 4CO2 + 6H2OA hydrocarbon (molecule of carbon and hydrogen) and oxygen (addedwith heat) always produces CO2 and H2O. This is combustion.

5) AgNO3 + NaCl −−→ NaNO3 + AgClTwo products with both being compounds impliesdouble displacement.


Practice: [See Section 2.5 Video]

1 Predict the products of the following reactions.

2 Balance the chemical equation.

1 CaCO3(s) −−→

2 C3H8(g) + O2(g) −−→

3 Al(s) + HCl(aq) −−→

4 MgO(s) + H2O(l) −−→

5 K2SO4(aq) + Ba(NO3)2(aq) −−→


Section 2.6 - The Activity Series & Solubility

Single Displacement reactions don’t always occur, even if the generalform is present.

Consider the following reactions:

NaCl + K −−→ KCl + Na

KCl + Na −−→ ?

The last reaction does not occur, because sodium (Na) is less reactivethan potassium (K).


General Rule: More reactive elements will generally be able to displaceelements that are less reactive. (This is on the back of the periodic table).

Any element on the table will displace an element below it.Mr. Palmarin Chapter 2 - Chemical Reactions 34 / 47

Example: In which of the following cases will a reaction not occur? Forthe reactions that you predict will occur, complete and balance theequation.

1) Al(s) + H2O(s) −−→ ? Al2O3 + H2

Will occur because Al is above H2 on the activity series.

2) Cu(s) + Hg(NO3)2(aq) −−→ ? Cu(NO3)2 + Hg

Will occur because Cu is one above Hg. Cu takes a 2+ chargebecause that’s its common charge.

3) Br2(aq) + MgI2(aq) −−→ ? MgBr2 + I2Anions replace anions. Here bromine (which is an anion) won’treplace magnesium but will replace iodine. It is above iodine on theactivity series (look to the right).

4) Br2(aq) + CaCl2(aq) −−→ ? No reaction

Bromine is lower down than chlorine; therefore, it won’t replacechlorine. When this occurs, simply write no reaction or N.R..


Ionic Compounds in Water

Example: Solid NaCl consists of Na+ and Cl– ions. What happens whenNaCl (table salt) is dissolved in water?


When NaCl dissolves in water, each ion separates from the solid structureand disperses throughout the solution. The ionic solid dissociates into itscomponent ions as it dissolves.

Dissociation is the process where ionic compounds dissolve in water andsplit up into their individual ions.

Example:

NaCl(s) −−→ Na+ + Cl–

Ba(NO3)2(s) −−→ Ba2+ + 2 NO –3

Al2(SO4)3(s) −−→ 2 Al3+ + 3 SO 2–4


Solubility

Solubility refers to the ability of a compound to dissolve in a solvent. Thecompound being dissolved is called the solute and the liquid doing thedissolving is called the solvent (usually water for ionic compounds).

Insolubility refers to a compound’s tendency to remain undissolved in asolvent.

Example:

Oil + water

Iced tea + water


Section 2.7 - Types of Double Displacement Reactions

There are three main types of double displacement reactions.

1 Reactions in which precipitates are formed.

2 Reactions that produce water.

3 Reactions that produce a gas.

Note: If a precipitate, water, or gas is NOT produced in a doubledisplacement reaction, no reaction has occurred.


1) Precipitation Reactions

A precipitate is an insoluble solid formed by a reaction. Reactions thatresult in the formation of an insoluble product are known as precipitationreactions.

Example: Pb(NO3)2(aq) + 2 KI(aq) −−→ PbI2(s) + 2 KNO3(aq)

How do we know if a compound will form a precipitate?


You must reference the Solubility Table (on the back of your periodictable) to determine the states of the products.

Note: All common ionic compounds of the Group 1 metals and of the ammonium

ion (NH +4 ) are soluble in water.


Note: A double displacement reaction will not have occurred if thesolubility rules indicate that:

Both products are precipitates

OR

Both products are aqueous (and cannot decompose further)


Example: Indicate which of the following double displacement reactionswill go to completion. Indicate the precipitate of the reaction (if any).

1) Pb(NO3)2 + AgCl −−→ ?

Here, the products come out to be PbCl2 and AgNO3. What are thestates of these products? Check your solubility table. Pb2+ isinsoluble with Cl– =⇒ PbCl2 is solid. Everything is soluble innitrate, therefore AgNO3 is aqueous. Therefore, this reaction occur.

2) Mg(NO3)2(aq) + NaOH(aq) −−→ ?

Products are Mg(OH)2 (is solid) and NaNO3 (is aqueous) =⇒reaction does occur.

3) NaOH(aq) + CaBr2(aq) −−→ ?

Products are NaBr and Ca(OH)2. Referencing the solubility table, bothproducts are aqueous. Therefore, this reaction does not take place.


2) Reactions that Produce Water

This a special type of double displacement reaction. It only occurs whenthe reactants include an acid and a base. This reaction is also known as aneutralization or acid-base reaction.

HA(aq) + BOH(aq) −−→ BA(aq) + H2O(l)

Example:

1) HCl(aq) + Ba(OH)2(aq) −−→ ?

The products are HOH (or H2O) and BaCl2. Water is not aqueous - it is aliquid. BaCl2 is aqueous. Therefore, since a liquid is produced, thisreaction will occur. (Write the products and try and balance it below).


Practice: Complete the following double displacement reactions.[See Section 2.7 Video]

1) H2SO4(aq) + LiOH(aq) −−→

2) HCl(aq) + NaOH(aq) −−→

3) H2SO4(aq) + NH4OH(aq) −−→


3) Reactions that Produce a Gas

These double displacement reactions produce an acid or a base. Recall:In decomposition, acids often decompose to form two products: anon-metal oxide (which will be a gas) and water, while bases decomposeto form metal-oxides (gases) and water.

These will be tricky because they will be multi-step.

Example:

1) K2CO3 + HNO3 −−→ ?

Here, the products become: KNO3 + H2CO3. So we get carbonic acidas one of the products. This can further decompose into H2O andCO2, which is a gas. Therefore, the products are: KNO3 + H2O + CO2

and this reaction will occur.


Practice: Complete the following double displacement reactions.[See Section 2.7 Video]

1) Na2CO3 + HCl −−→

2) CaSO4 + KOH4−−→


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