Physical and Chemical Changes

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All matter, regardless of state, undergoes physical and chemical changes. These changes can be microscopic or macroscopic.

Physical and chemical properties may be intensive or extensive.

Intensive properties such as density, color, and boiling point do not depend on the size of the sample of matter and can be used to identify substances.

Extensive properties such as mass and volume do depend on the quantity of the sample.

Physical properties are those that we can determine without changing the identity of the substance we are studying.

The physical properties of sodium metal can be observed or measured. It is a soft, lustrous, silver-colored metal with a relatively low melting point and low density.

Hardness, color, melting point and density are all physical properties.

A physical change occurs when the substance changes state but does not change its chemical composition. For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)

Melting pointBoiling pointVapor pressureColorState of matter

Density Electrical

conductivitySolubilityAdsorption to a

surfaceHardness

Chemical properties describe the way a substance can change or react to form other substances. These properties, then, must be determined using a process that changes the identity of the substance of interest.

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

A chemical property must describe how some substance REACTS or DOES NOT REACT with other substances.

In other words, they describe how a substance will be changed or will not be changed when it interacts with other substances.

One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens.

In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.

A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc. You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (change in color, change in temperature, formation of a gas, emission of light, formation of a precipitate).

Reaction with acidsReaction with bases

(alkalis)Reaction with

oxygen (combustion)

Ability to act as oxidizing agent

Ability to act as reducing agent

Reaction with other elements

Decomposition into simpler substances

Corrosion

Evidence of Chemical ChangeEvidence of Chemical Change

Bubbles of gas appearA precipitate formsA color change occursThe temperature changesLight is emitted

Create a Venn diagram to compare and contrast physical and chemical properties

Two Important Physical PropertiesTwo Important Physical Properties

States of Matter

Density of Matter

•Solids•Liquids•Gases•Plasma

(And how the Kinetic Molecular Theory affects each)

•Have a definite shape•Have a definite volume

Molecules are held close together and there is very little movement between them.

Kinetic Molecular Theory

•Have an indefinite shape•Have a definite volume

Kinetic Molecular Theory:Atoms and molecules have more space between them than a solid does, but less than a gas (ie. It is more “fluid”.)

•Have an indefinite shape•Have an indefinite volume

Kinetic Molecular Theory:

Molecules are moving in random patterns with varying amounts of distance between the particles.

At 100°C, water becomes water vapor, a gas. Molecules can move randomly over large distances.

Below 0°C, water solidifies to become ice. In the solid state, water molecules are held together in a rigid structure.

Between 0°C and 100 °C, water is a liquid. In the liquid state, water molecules are close together, but can move about freely.

Phases of MatterPhases of MatterConcept MapConcept Map

PhaseChanges

Solids

Liquids

Gases

Definiteshape Fixed

volume

Fixedvolume

Takesshape ofcontainer

Indefiniteshape

Indefinitevolume

Compressibility

On earth we live upon an island of "ordinary" matter. The different states of matter generally found on earth are solid, liquid, and gas. We have learned to work, play, and rest using these familiar states of matter. Sir William Crookes, an English physicist, identified a fourth state of matter, now called plasma, in 1879.

Plasma is by far the most common form of matter. Plasma in the stars and in the tenuous space between them makes up over 99% of the visible universe and perhaps most of that which is not visible.

EXAMPLES:

•Computer chips and integrated circuits

•Computer hard drives

•Electronics

•Machine tools

•Medical implants and prosthetics

•Audio and video tapes

•Aircraft and automobile engine parts

•Printing on plastic food containers

•Energy-efficient window coatings

•High-efficiency window coatings

•Safe drinking water

•Voice and data communications components

•Anti-scratch and anti-glare coatings on eyeglasses and other optics

DensityDensity

Density = mass (g) D = g or g volume (ml) ml cm3

Note ml = cm3

m

D v

Learning Check D1Learning Check D1

Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupiesa volume of 2.22cm3?

1) 2.25 g/cm3

2) 22.5 g/cm3

3) 111 g/cm3

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Solution Solution

2) Placing the mass and volume of the osmium metal into the density setup, we obtain

D = mass = 50.00 g = volume 2.22 cm3

= 22.522522 g/cm3 = 22.5 g/cm3

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Volume DisplacementVolume DisplacementA solid displaces a matching volume of water when the solid is placed in water.

33 mL25 mL

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Learning Check Learning Check

What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? 1) 0.2 g/ cm3 2) 6 g/m3 3) 252 g/cm3

33 mL 25 mL lecturePLUS Timberlake 33

Solution Solution 2) 6 g/cm3

Volume (mL) of water displaced = 33 mL - 25 mL = 8 mL

Volume of metal (cm3) = 8 mL x 1 cm3 = 8 cm3

1 mLDensity of metal = mass = 48 g = 6 g/cm3

volume 8 cm3

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Learning Check3Learning Check3

Which diagram represents the liquid layers in the cylinder?(K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)

1) 2) 3)

lecturePLUS Timberlake 35K

K

W

W

W

V

V

VK

Solution Solution

(K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)

1)

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V