1 Mr. ShieldsRegents Chemistry U03 L5

2 Properties Properties can further be categorized into 2 types: The first is Physical The other is Chemical

3 Physical Properties Let’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 hardness Taste mp bp luster These are all properties than can be observed w/o changing anything.

4 Chemical Properties Chemical Properties are things that can not be observed without altering the identity of the Substance. What does this mean? Ex. Chemical property “Sodium can react w/ Chlorine” These are chemical properties of Na & Cl 2 The fact that iron will rust in water is also an Example of a chemical property of Fe

5 Properties of Copper Physical Prop.  Reddish brown  Shiny  Malleable  Ductile  Good Conductor  Density = 8.92 g/cm 3  MP = 1085  C  BP = 2570  C Chemical Prop.  Reacts with CO 2 to form green copper carbonate  Forms a deep blue solution when in contact with NH 3  Forms a new blue substances with HNO 3.

6 Physical Change Besides Physical and Chemical Properties Matter can undergo Physical and Chemical Change. A PHYSICAL CHANGE is something done that doesn’t alter the identity of the substance What are some examples of physical change?

7 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?

8 Dissolving  Think of sugar in water. You still have sugar – you just break it down into single molecules surrounded by water molecules  C 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq) (crystal) (in sol’n – molecule)

9 Chemical Change A Chemical change is something DONE that does “alter” the identity of the substance. Chemical change is also known as a “CHEMICAL REACTION” Indicators of Chemical Change: Heat, light, Gas, solid forms, Sound, color change etc.

10 Chemical Change Ex. Of Chemical change: 2Na + Cl 2  2 NaCl Have we altered the identity of these 2 elements? +

11 Reaction of Magnesium Mg will burn in Oxygen - A Chemical Property 2Mg + O 2  2MgO - A Chemical Change Metal Gas Powder Let’s try it!

12 The LAW OF CONSERVATION OF MASS It was originally defined by Antoine Lavoisier in 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 operation there 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 that is founded all the art of performing chemical experiments; in all such must be assumed a true equality or equation between constituents of the substances examined, and those resulting from their analysis."

13 Conservation of Mass Lets look at the reaction of Magnesium with Oxygen 2Mg + O 2  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 mass Before the rxn = total mass after the reaction!

14 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 Cl 2 ? 2Na + Cl 2  2 NaCl 2 Na atoms + 2 Cl atoms  2 Na atoms + 2 Cl atoms Is mass conserved? If sodium and chlorine completely react to form salt. How much salt is formed? 2Na + Cl 2  2 NaCl 46g g  ? g … Why?

15 Conservation of Mass If 92 grams of Na react with Chlorine to form grams of sodium chloride how much Chlorine reacted with the sodium? 2Na + Cl 2  2 NaCl 92g + ?g  233.8g Cl 2 = 141.8g … Why? Problem: ?!