1Mr. Shields Regents Chemistry U03 L5

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Properties

Properties can further be categorized into 2 types:

The first is Physical

The other is Chemical

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Physical PropertiesLet’s define a Physical Property:

Physical properties are things that can be observed w/o altering the identity of the substance.

What would be some examples of this? …

Density color odor hardnessTaste mp bp luster

These are all properties than can be observed w/ochanging anything.

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Chemical PropertiesChemical Properties are things that can not beobserved without altering the identity of theSubstance. What does this mean?

Ex. Chemical property “Sodium can react w/ Chlorine”

These are chemical properties of Na & Cl2

The fact that iron will rust in water is also anExample of a chemical property of Fe

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Properties of CopperProperties of CopperPhysical Prop.

Reddish brown Shiny Malleable Ductile Good Conductor Density = 8.92

g/cm3

MP = 1085C BP = 2570C

Chemical Prop.

Reacts with CO2to form green copper carbonate

Forms a deep blue solution when in contact with NH3

Forms a new blue substances with HNO3.

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Physical ChangeBesides Physical and Chemical Properties Mattercan undergo Physical and Chemical Change.

A PHYSICAL CHANGE is something done that doesn’talter the identity of the substance

What are some examples of physical change?

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Physical Change In a physical change, the form or appearance of

the sample may change but the identity remains the same.

– Remember PHASE CHANGES? They are examples of physical change.

– Cutting, crushing, grinding to a powder are all physical changes.

– Dissolving a substance (to form a solution) is a physical change. Why?

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DissolvingThink of sugar in water. You

still have sugar – you just break it down into single molecules surrounded by water molecules

C6H12O6(s) C6H12O6(aq)(crystal) (in sol’n – molecule)

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Chemical Change

A Chemical change is something DONE that does“alter” the identity of the substance. Chemicalchange is also known as a

“CHEMICAL REACTION”Indicators of Chemical Change: Heat, light, Gas, solidforms, Sound, color change etc.

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Chemical Change

Ex. Of Chemical change:

2Na + Cl2 2 NaCl

Have we altered the identity of these 2 elements?

+

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Reaction of Magnesium

Mg will burn in Oxygen - A Chemical Property

2Mg + O2 2MgO - A Chemical ChangeMetal Gas Powder

Let’s try it!

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The LAW OF CONSERVATION OF MASSIt was originally defined by Antoine Lavoisier in 1785. In that year he wrote…

So what exactly does this mean?

Matter can neither be created nor destroyed!

"Nothing is created, either in the operations of art or in those of nature,and it may be considered as a general principle that in every operationthere exists an equal quantity of matter before and after the operation; that the quality and quantity of the constituents is the same, and that what happens is only changes, modifications. It is on this principle thatis founded all the art of performing chemical experiments; in all suchmust be assumed a true equality or equation between constituents ofthe substances examined, and those resulting from their analysis."

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Conservation of Mass

Lets look at the reaction of Magnesium with Oxygen

2Mg + O2 2MgO

2 atoms of Mg reacts with 2 atoms of O. These form 2 Magnesium Oxide molecules which also total 2 atoms of Mg and 2 atoms of O

Matter has been CONSERVED. No atoms were Lost and None were gained. Therfore total massBefore the rxn = total mass after the reaction!

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Conservation of Mass Let see how we use the Law of Conservation of

mass to solve problems. What happens to mass when we react Na with Cl2?

2Na + Cl2 2 NaCl

2 Na atoms + 2 Cl atoms 2 Na atoms + 2 Cl atomsIs mass conserved?

If sodium and chlorine completely react to form salt. How much salt is formed?2Na + Cl2 2 NaCl46g + 70.9g ?

116.9 g … Why?

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Conservation of Mass

If 92 grams of Na react with Chlorine to form 233.8 grams of sodium chloride how much Chlorine reacted with the sodium?

2Na + Cl2 2 NaCl92g + ?g 233.8g

Cl2 = 141.8g … Why?

Problem:

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