introduction
TRANSCRIPT
WHAT IS THERE TO KNOW ABOUT CHEMISTRY ?
CHEMISTRY
Matter
Composition
change
energy
physical
chemical
Laws/Principles/Theories
properties
has
has
undergoes
Relates to
Can bestudies
Predict interpret
effectsstudies
basis of distinction : composition
Matter
composition structure
properties reactions
• Matter – anything that has mass and occupies space• Laws/Theories- mathematical statements of behaviour of
matter• Properties- characteristics that describe matter; use to
determine its usefulness» Physical- properties which can be
observed/measured without a change in the composition of the substance
» Chemical – properties which can be observed/measured only after a change in the composition of the substance
» Intensive – does not depend upon amount of the substance
» Extensive – depends upon amount of the substance
Every pure substance has its own unique set of properties(
• - serve to distinguish it from all other substances
• Are intensive properties-properties which are independent of amount of the substance
• Chemical properties are intensive properties
• Fact: • Sample weighs 4.02 g,
has a volume 0f 229 mL. • Tells nothing about the
identity of the substance
• Mass & volume – extensive properties-they depend on amount
Beyond that the substance may be identified on the basis of its chemical properties
Chemical change- change in the composition of the substanceChemical equation- expression/language of a chemical change
• Matter is anything that has mass and occupies space.
Matter can be invisible.Air is matter, but it cannot be seen.
Matter appears to be continuous and unbroken.Matter is actually discontinuous. It is made up of tiny
particles call atoms.
An apparently empty test tube is submerged, mouth downward in water. Only a small volume of water rises into the tube, which is actually filled with invisible matter–air.
Classification of matter:
A pure substance is always homogeneous in composition, whereas a mixture always contains two or more substances and may be either homogeneous or heterogeneous.
Substance
• A particular kind of matter that has a fixed composition and distinct properties.
• Examples• ammonia, water, and oxygen.
Homogeneous Matter
Matter that is uniform in appearance and with uniform properties throughout.
Examples
ice, soda, solid gold
Heterogeneous Matter
• Matter with two or more physically distinct phases present.
• Examples• ice and water, wood, blood
Homogeneous
Heterogeneous
Phase
• A homogenous part of a system separated from other parts by physical boundaries.
• Examples• In an ice water mixture ice is the solid phase
and water is the liquid phase
Mixture
• Matter containing 2 or more substances that are present in variable amounts. Mixtures are variable in composition. They can be homogeneous or heterogeneous.
Homogeneous Mixture (Solution)
• A homogeneous mixture of 2 or more substances. It has one phase.
• Example• Sugar and water. Before the sugar and water
are mixed each is a separate phase. After mixing the sugar is evenly dispersed throughout the volume of the water.
Heterogeneous Mixture
• A heterogeneous mixture consists of 2 or more phases.
• Example• Sugar and fine white sand. The amount of
sugar relative to sand can be varied. The sugar and sand each retain their own properties.
Mixture of iron and sulfur
Compound of iron and sulfur
Has no definite formula: consists of Fe and S.
FeS
Contains Fe and S in any proportion by mass.
63.5% Fe and 36.5% S by mass.
Fe and S can be separated by physical means.
Fe and S can be separated only by chemical change.
Energy – driving force of all changes/capacity to do work
Energy
Types
Potential – stored energy
Energy at work
motion
position
Vibrational motionOf a plucked guitar
Translational motion Of a moving bullet
Kinetic motion ofMoving molecules
Due to
has
HEAT
MostCommon form
Thermodynamics
• Literally means “movement” of heat
• As it applies to chemistry it refers to all aspects of chemical systems that involve changes in energy of any type.
Laws of Thermodynamics
• First Law• Defines the energy
change for a process in terms of the difference between heat absorbed and work done
• Second Law• Puts a restriction on the
amount of heat that may be converted into work and defines a quantity called entropy
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In all chemical changes, matter either absorbs or releases energy.
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Law of Conservation of Energy
Energy can be neither created nor destroyed, though it can be transformed from one form of energy to another form of energy.
Bookeeping of energy
Situation Seem to Be Actual Direction of Energy Flow
A + B >>> C
C < A + BEnergy was destroyed
Some of A and B was converted into energy and was inevitably lost as HEAT
EXOTHERMIC
C > A + B Energy wascreated
A and B absorbed Heat from outside to form C
ENDOTHERMIC
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An energy transformation occurswhenever a chemical change occurs.
• If energy is absorbed during a chemical change (endothermic ), the products will have more chemical potential energy than the reactants.
• If energy is given off in a chemical change (exothermic ), the products will have less chemical potential energy than the reactants.
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Energy Release From Chemical Sources
Type of Energy Energy Source
Electrical Storage batteries
Light A lightstick. Fuel combustion.
Heat and Light Combustion of fuels.
Body Chemical changes occurring within body cells.
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Chemical Changes Caused byAbsorption of Energy
Type of Energy
Chemical Change
ElectricalElectroplating of metals. Decomposition of water into hydrogen and oxygen
Light Photosynthesis in green plants.
Do all changes spontaneously occur(bound to happen)?
What will bound to happen in each of the following situation?
firewood
ice
Attainment of low energy state
Endothermic heat flowIncrease in entropy
Exothermic heat flow
ice
firewood
What are the reasons behind in the spontaneous changes of the above situations ?
The rationale of an spontaneous change areAttainment of low energy state
Attainment of high entropy
Entropy- degree of disorderliness