11 Chem: 8.2.4 The Chemical Earth

4.Energy is required to extract elements from their naturally occurring sources

What can you recall about Physical and Chemical Changes??

• Create a mind map in your books about what you already know.

identify the differences between physical and chemical change in terms of rearrangement of

particles

• http://education-portal.com/academy/lesson/states-of-matter-and-chemical-versus-physical-changes-to-matter.html

•

Physical Change

• In a physical change the intermolecular bonds (which are fairly weak) are broken. In a physical change no new substances are formed, rather the substance changes its state. For example water boiling.

• In this example there are no new substances formed and thus there is no rearrangement of particles within molecules.

• Rather energy is provided to the molecules via the heat which causes them to have enough energy to separate themselves from one another (i.e. the intermolecular bonds are broken).

• The result is that some water particles leave the surface of the liquid (can be seen when the water evaporates).

• In a physical change the energy change is relatively small. Also a physical change is easy to reverse (condensation of water). In a physical change there are mass changes. (I.e. the mass of the substance will change after a physical change)

• What are the intermolecular forces? Please list them with a description of what they are.

Chemical Change

• In a chemical change however the intramolecular bonds (which are relatively strong) are broken. In a chemical change, new substances are formed. An example of this can be seen during the electrolysis of water.

• In this example, two new substances, O2 and H2 are formed. Thus there is a clear rearrangement of particles. In electrolysis, there is a lot more energy provided to the water molecules, enough energy is provided to break the intramolecular bonds between the hydrogen and the oxygen

• In the apparatus the negative oxygen ions are attracted to the positively charged cathode where as the positive hydrogen ions are attracted to the negatively charged cathode. Thus electrolysis proved enough energy to split intramolecular bonds, causing the re-arrangement of particles to form two new substances.

Summarise the difference between the boiling and electrolysis of water as an example of the

difference between physical and chemical changes

Boiling Electrolysis

Physical Change Breaks intermolecular

forces Changes physical state

(liquid to gas) Relatively low amount of

energy needed

Chemical change Breaks intramolecular

forces Relatively large amount of

energy needed

Student Homework:

• Conquering chemistry:• Pg 70; Q1 & 3

identify light, heat and electricity as the common forms of energy that may be released or absorbed during the

decomposition or synthesis of substances and identify examples of these changes occurring in everyday life

• Decomposition is the breaking down of compounds into simpler substances.

• Synthesis is the joining of simpler substances to form more complex substances through chemical reactions.

• Heat, light and electricity are common forms of energy released or absorbed during various synthesis and decomposition reactions.

• Heat may be absorbed or released in endothermic and exothermic reactions, respectively.

Examples of Decomposition

Example Method used Energy absorbed or released

Production of metals from their ores. Eg. Copper from copper carbonate

Heat in furnace Heat energy is absorbed by the copper carbonate, resulting in decomposition

Development of film Action of sunlight on silver bromide (film)

Solar energy (light) is used to decompose silver bromide.

The combustion of magnesium  

Burn magnesium in air Results in a brilliant light and considerable amounts of heat being released.

Production of aluminium from aluminium oxide (in bauxite)

Pass electricity through molten aluminium oxide

Electrical energy is absorbed

Examples of Synthesis

Example Method used Energy absorbed or released

The rusting of iron Iron reacts with oxygen in the air, in the presence of water to form iron (III) oxide

Energy released in the form of heat

Photosynthesis Carbon dioxide and water combine to form glucose and oxygen

Light energy is absorbed and heat energy is released

Formation of nitrogen oxides in the atmosphere

Lighting causes atmospheric nitrogen to combine with oxygen to form nitrogen monoxide

Electrical energy is absorbed

Burning of coal or coke to produce electricity or to make steel

Coal is heated in furnaces Heat energy is absorbed to the start the reaction. Heat energy is also produced.

Observe the Electrolysis of Water

• https://www.youtube.com/watch?v=T-OwWOYHhMI

explain that the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction, or bond, between

them

• The amount of energy needed to decompose chemical compounds and mixtures is indicative of the strength of the bonds. Stronger bonds require more energy to break them, a prominent example being the difference between boiling water and electrolysis.

• What bonds are being broken with the boiling of water?

• What are the bonds being broken in the electrolysis of water?

• Another example is that mercury oxide can be easily decomposed by heating whereas potassium oxide cannot. This indicates that the potassium is more reactive than the mercury so it forms a stronger intramolecular attraction. Therefore more energy is required to overcome the strong attraction between atoms.

• Activity: Please write a balanced equation for the reactions mentioned above

• Intramolecular bonds are very strong and therefore require more energy to break than intermolecular bonds.

• This can be seen in example of the boiling/electrolysis of water. Heat energy is enough to break the intermolecular bonds to cause the change of state, but electrical energy is needed to break the intramolecular bonds to create two new substances.

Student Homework

• Conquering Chemistry:• Pg 75: Qs 5, 6, 7 & 10

Household Chemicals NaHCO3 Sodium Carbonate

NaClO Sodium Hypochlorite

NH3 Nitrogen Trihydride

NaCl Sodium Chloride

H2O2 Hydrogen Peroxide

Household Chemicals NaHCO3 Baking Soda

NaClO Bleach

NH3 Ammonia

NaCl Salt

H2O2 Hydrogen Peroxide

Nomenclature Terms Binary Compound :

contains 2 elements

Binary Ionic Compound : a metal and a nonmetal -> metal named first If metal has more than one charge must indicate charge with

(Roman numerals) or

Latin endings

-ous = lower charge - ic = higher charge

Nomenclature TermsBinary Covalent Compound:

two nonmetals

Least electronegative element named first

Second element has -ide ending

Greek prefixes indicate subscripts

1 = mono- 6 = hexa-2 = di- 7 = hepta-3 = tri- 8 = octa-4 = tetra- 9 = nona-5 = penta-10 = deca-

Nomenclature TermsNonbinary Compound:

more than two elements

- probably contains polyatomic ion(s)

- Name the polyatomic cation first- Name the polyatomic anion second

- MUST KNOW the polyatomic ions by name and formula to recognise them

Nomenclature Flow Chart

Single-Charge Multiple-Charge Metal Metal

Name the metal

Indicate metal charge by (Roman #) or Latin

name (-ous or –ic)

+ 1 nonmetal + 2 nonmetals

Name the polyatomic ion Nonmetal name

with –ide ending

*Metal + Nonmetal

Chemical Formula

2 Nonmetals

1) Use Greek prefixes to indicate subscripts

2) second element –ide ending

H + Nonmetal(s)

Name as acids

* Treat NH4+ as a metal when

naming compounds

Naming of Acids• If anion does not contain oxygen:

• Start with Hydro-• Add –ic to the end• Ex: HCl: Cl- is chloride, so the acid is Hydrochloric acid

• If anion contains oxygen:• Look at the ending

• If –ite, use anion root and -ous• Ex: HNO2: NO2

- is nitrite, so the acid is Nitrous acid

• If –ate, use anion root and -ic• Ex: H2SO4: SO4

2- is sulfate, so the acid is Sulfuric acid

Nomenclature PracticeName the following

compounds: Ba(OH)2

NaC2H3O2

Fe3(PO4)2

SO3

LiF

Fe3(PO4)2

CaS

MgSO4

K2SO3

P2O5

N2O

Student Homework

• Conquering Chemistry• Pg 79: Qs 11, 12, 13, 14, 15 & 16• Pg 81: Qs 17, 18 & 19• (this homework is very important – the

more practice you have at chemical formulas and equations the easier chemistry will be in the future!)