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Lecture 1

CHEM 217 Lecture Notes - Lecture 1: Si Derived Unit, Mathematical Constant, Intensive And Extensive Properties

Course Code
CHEM 217

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Unit 1
1 . 1 C H A N G E S
oPhysical changes
oDon’t alter chemical composition
Ex. water boiled – vapour is still water
oA physical property is displayed without changing composition
oChemical changes
oAlter chemical structure
Ex. Rusting of iron – iron atoms combine with O2 to form iron II oxide
oA chemical property changes composition via chemical change
oExample : Gasoline
oOdour is a physical property
Physical properties: odour, taste, colour, appearance, points (boiling/freezing),
oCombustibility is a chemical property
Chemical properties: corrosiveness, flammability, acidity, toxicity
1 . 2 E N E R G Y
oTotal energy of an object is a sum of its kinetic and potential energy (associated with position or
oi.e. holding rock in air has potential energy -> drop and it becomes kinetic energy ->
lands and loses energy as thermal energy
oThermal energy is associated w/temperature and is a type of kinetic energy because it’s
associated with movement of atoms/molecules that make up an object.
oLaw of conservation – not created nor destroyed
oTendency of systems with high potential energy to change in a way that lowers that potential
oEx. item high up tends to be unstable and contain a lot of localized potential energy ,’,
falls and becomes more stable
oAlso happens with chemical substances ex. gas molecules have high potential energies
so they tend to undergo changes (combustion in this case) that lower their potential
energy - as energy of these molecules is released some can be harnessed to do work
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like moving vehicles. When gas combusts resulting molecules have less energy and
transfers energy (mostly as heat) to surroundings.
oChemical potential energy
oArises from (primarily) electrostatic forces between electrically charged particales [ (p+)
(e-) ]
1 . 3 U N I T S O F M E A S U R E M E N T
oInternational system of units (SI) -> subsystem of metric system
m, kg, s, K, mol, A, cd
oKg (mass) -> different from weight – measure of the quantity of matter within it while weight is
measure of gravitational pull. Weight changes on the moon but mass stays the same
oK – temp. avoids negatives by assigning 0K to coldest possible temp – absolute zero. That is the
temperature at which translational motion of molecules stops.
o0C = 273.15K
oScientific notation allows to express very large or small quantities in compact manner.
oPrefix multipliers change the value of the unit by powers of 10 (Table)
oEither combinations of different units or multiples of units of the same type.
oEx. speed in metres per second (m s-1)
oVolume volume is a measure of space -> any unit of length when cubed becomes a unit of
oRatio of its mass (m) to its volume (v)
Density = mass OR d = m
volume v
oCharacteristic physical property of materials because it depends on the temperature
oIt is an intensive property – independent of the amount of the substance
oMass is an extensive property – depends on amount of substance
oSI derived unit for density is kg m-3
oDensity of liquids and solids mostly expresside in g cm-3 or g mL-1(1cm3=1mL)
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