topic_1_stoichiometric_relationships_1.1_to_1.3.pptx - IB...

Topic 1 Stoichiometric relationships
IB CHEMISTRY

1.1 Introduction to the particulate
nature of matter and chemical change
• Atoms of different elements combine in fixed ratios to form
compounds, which have different properties from their
component elements.
• Mixtures contain more than one element and/or compound
that are not chemically bonded together and so retain their
individual properties.
• Mixtures are either homogeneous or heterogeneous.
• Deduction of chemical equations when reactants and products
are specified.
• Application of the state symbols (s), (l), (g) and (aq) in
equations.
• Explanation of observable changes in physical properties and
temperature during changes of state.
OBJECTIVES

Law vs theory
Both are developed from experiments. Both have
exceptions. Both can be modified or rejected.
Theory: An explanation that provides an
understanding across a range of phenomena and
disciplines.
Law: A description of regular patterns of behavior.

Law of definite proportions
•
‘A compound always contains the
same proportion of elements by
mass’
•
Joseph Louis Proust, French
chemist
•
1794 showed experimentally that
artificial and natural copper
carbonate had the same
proportion of weights between Cu,
C, and O.

But... what about this
compound?
•
Berzelius a Swedish
chemist disagreed with
Proust.
•
Non-stoichiometric
compounds (mainly
inorganic solids and
polymers) as well as
isotopes form exceptions
to the rule
•
Eg. FeO is usually Fe
0.84
O
due to Fe in different
states (Fe
2+
and Fe
3+
)

Principle of Occam’s razor
William of Ockham was and English
monk (1287-1347 CE).
‘A theory should be as simple as
possible while maximizing
explanatory power.’
(Shaving away the unnecessary)
Why did Proust win out over
Berzelius?

Element: A substance composed of atoms having an
identical number of protons in each nucleus.
Atom: Smallest part of an element
Compound: 2 or more elements chemically bonded
together
Mixtures: Contain more than one element an/or
compound that are not chemically bonded together
and so retain their individual properties. Two types:
Homogenous – have uniform properties
Heterogenous – have non-uniform properties
Terminology

Terminology
•
Solid (s), Liquid (l), Gas (g), Aqueous (aq) –
dissolved in water

States of matter

Changes of state
melting
freezing
Vaporization
(boiling vs
evaporation)
condensation
sublimation
deposition

Heating curves
•
SI unit for temperature is the kelvin (K) which is
°C + 273 .
150
100
50
0
-50
Time/s
This flat line demonstrates the
substance is pure
Energy added at phase change
goes into breaking interparticle
forces NOT raising temperature

Law of multiple proportions
•
‘If two elements form more than one
compound between them, then the
ratios of the masses of the second
element which combine with a fixed
mass of the first element will be ratios of
small whole numbers’ eg. CO and CO
2
•
John Dalton, English chemist
•
An improvement built upon Proust’s law
of definite proportions and Lavoisier’s law
of conservation of mass. These three laws
then then form the basis for chemical
formulae, names, and stoichiometry!

Experimental evidence for stoichiometry: