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

22

In all chemical changes, matter either absorbs or releases energy.

23

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

25

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.

26

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.

27

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