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Unit 2: MatterUnit 2: Matter

Properties and ChangesProperties and Changes

CHEMISTRYCHEMISTRY

August 29, 2007August 29, 2007

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BrainteaserBrainteaser�� Define physical and chemical change Define physical and chemical change

(in your own words).(in your own words).

�� Is this picture of a physical or a Is this picture of a physical or a

chemical change?chemical change?

––Explain yourExplain your

reasoningreasoning

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Properties of Matter—Substances

• Matter that has a uniform and unchangingcomposition is called a substance, also known as a pure substance.

• For example:

– Table salt

– Water

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� Why is seawater NOT an example of a substance?

� Seawater, on the other hand, is not a substance because samples taken from different locations will probably have differing compositions.

– That is, they will contain differing amounts of water, salts, and other dissolved substances.

Properties of Matter—Substances

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Physical Properties of Matter

• A physical property is a characteristic that can be observed or measured withoutchanging the sample’s composition. Physical properties describe pure substances, too.

NOT IN NOTES… SORRY

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Physical Properties & ChangesPhysical Properties & Changes

�� Characteristics of a substance that Characteristics of a substance that

can be observed without altering the can be observed without altering the

identity of the substance.identity of the substance.

–– StateState, , densitydensity, color, , color, odorodor, melting , melting

point, point, boiling pointboiling point, luster, conductivity, , luster, conductivity,

brittlenessbrittleness, malleability, malleability. .

NOT IN NOTES… SORRY

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Physical ChangePhysical Change

�� Does not Does not alteralter the identity of a substancethe identity of a substance

–– Crushing, tearing, changes of state (solid to Crushing, tearing, changes of state (solid to

liquid to gas)liquid to gas)

NOT IN NOTES… SORRY

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Extensive and Intensive Properties

• Physical properties can be further described as being one of two types.

– Extensive properties are dependentupon the amount of substance present.• For example, mass, which depends on the amount of substance there is, is an extensive property.

• Length and volume are also extensive properties.

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Extensive and Intensive Properties

• Intensive properties are independentof the amount of substance present.

– Density is an example of an intensive property of matter.

• Density of a substance (at constant temperature and pressure) is the same no matter how much substance is present.

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Chemical Properties of Matter

• Chemical property : The ability of a substance to combine with or change into one or more other substances.

– Rusting is an example of a chemical property of iron

• Similarly, the inability of a substance into change into another substance is also a chemical property.

– Resistance of iron to undergo change in the presence of nitrogen.

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Chemical ChangesChemical Changes

�� Characteristics of a substance that cannot Characteristics of a substance that cannot

be be observedobserved without altering the identity of without altering the identity of

the substance.the substance.

–– ReactivityReactivity, flammability, reaction types, flammability, reaction types

�� Alter the identity or chemistry of substanceAlter the identity or chemistry of substance

–– Burning, cooking, rustingBurning, cooking, rusting

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States of MatterStates of Matter

• The physical state of a substance is a physical property of that substance.

• Each of the three common states of matter can be distinguished by the way it fills a container.

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SolidsSolids

• A solid is a form of matter that has its own definite shape and volume.

–For example: Wood, iron, paper, and sugar

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SolidsSolids

• The particles of matter in a solid are very tightly packed; when heated, a solid expands, but only slightly.

• Because its shape is definite, a solid may not conform to the shape of the container in which it is placed.

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LiquidsLiquids

• A liquid is a form of matter that flows, has constant volume, and takes the shape of its container.

– Examples: Water, blood, mercury

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LiquidsLiquids• The particles in a liquid are not rigidly held in place and are less closely packed than are the particles in a solid.

• This allows a liquid to flow and take the shape of its container, although it may not completely fill the container.

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LiquidsLiquids

• Because of the way the particles of a liquid are packed, liquids are virtually incompressible. Like solids, liquids tend to expand only slightly when heated.

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GasesGases• A gas is a form of matter that flows to conformto the shape of its container and fills the entirevolume of its container.

• Compared to solids and liquids, the particles of gases are very far apart.

• Because of the significant amount of space between particles, gases are easily compressed.

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PlasmaPlasma

�� Plasmas or ionized gases can exist at Plasmas or ionized gases can exist at

temperatures starting at several thousand temperatures starting at several thousand

degrees Celsius (degrees Celsius (°°C). C).

–– Two examples of plasma are the charged air Two examples of plasma are the charged air

produced by produced by lightninglightning, and a , and a starstar such as our such as our

own own sunsun..

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Physical Changes

• A substance often undergoes changes that result in a dramatically different appearance yet leave the composition of the substance unchanged.

• An example is the crumpling of a sheet of aluminum foil.

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Chemical ChangesChemical Changes

• Chemical properties relate to the ability of a substance to combine with or change into one or more substances.

• A process that involves one or more substances changing into NEW substances is called a chemical change, which is commonly referred to as a chemical reaction.

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Chemical ChangesChemical Changes

• The new substances formed in the reaction have different compositions and different propertiesfrom the substances present before the reaction occurred.

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Chemical ChangesChemical Changes

� Rust is a chemical combination of iron and oxygen.

� In chemical reactions, the starting substances are called reactants and the new substances that are formed are called products.

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Conservation of MassConservation of Mass

• By carefully measuring mass before and after many chemical reactions, it was observed that, although chemical changes occurred, the total mass involved in the reaction remained constant.

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Conservation of massConservation of mass

• The law of conservation of massstates that mass is neither created nor destroyed during a chemical reaction—it is conserved.

• The law of conservation of mass is one of the most fundamental concepts of chemistry.

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Conservation of MassConservation of Mass

• The equation form of the law of conservation of mass is:

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Review QuestionsReview Questions

� Identify each of the following as an example

� of a chemical change or a physical change.

�� Moisture in the air forms beads of water

� on a cold windowpane.

� An electric current changes water into

� hydrogen and oxygen.

� Yeast cells in bread dough make carbon

� dioxide an ethanol from sugar.

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Review QuestionsReview Questions

� A reaction between sodium hydroxide and hydrogen chloride gas produces sodium chloride and water. A reaction of 22.85 g of sodium hydroxide with 20.82 g of hydrogen chloride gives off 10.29 g of water. What mass of sodium chloride is formed in the reaction?