Properties of Matter

Transcription

1 Properties of Matter Chapter 4 Hein and Arena Version 1.0 Eugene Passer Chemistry Department Bronx Community 1 College John Wiley and Sons, Inc

2 Properties of Substances 2

3 Properties of a Substance A property is a characteristic of a substance. A substance has both physical and chemical properties. Recall that a substance is a particular kind of matter. It has a fixed composition and distinct properties. 3

4 Physical Properties 4

5 Physical properties are inherent characteristics of a substance that are determined without changing its composition. taste color physical state melting point boiling point 5

6 Chemical Properties 6

7 Chemical properties describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition. Will it burn in oxygen. Will it support the combustion of certain other substances. Can it be used as a disinfectant. Can it combine with sodium to form sodium chloride, NaCl. 7

8 Physical Changes 8

9 Physical Changes Changes in physical properties (such as size, shape and density) or changes in the state of matter without an accompanying chemical change are physical changes. Examples: tearing of paper change of ice into water change of water into steam heating platinum wire Note that no new substance(s) are formed. 9

10 Chemical Changes 10

11 In a chemical change, new substances are formed that have different properties and composition from the original material. 11

12 Formation of Copper(II) Oxide Heating The formation a copper ofwire copper(ii) in a Bunsen oxide burner from copper causes and oxygen the copper is a chemical to lose its change. original appearance and The become copper (II) a black oxide material. is a new substance with properties that are different from copper. 12

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14 Chemical Equations 14

15 The Information present in a Balanced Chemical Equation Species present as reactants and products (i.e. atoms, ions, molecules, etc.) Amounts present (i.e. moles) Stoichiometry (i.e. mole ratios) Direction of reaction (i.e. favored) Reaction conditions (i.e. heat) 15

16 Water decomposes into hydrogen and oxygen when electrolyzed. reactant yields products 16

17 Chemical symbols can be used to express chemical reactions 17

18 Water decomposes into hydrogen and oxygen when electrolyzed. 2H 2 O 2H 2 O 2 reactant yields products 18

19 Copper plus oxygen yields copper(ii) oxide. heat 2Cu O 2 2CuO reactants yield product 19

20 Conservation of Mass 20

21 No change is observed in the total mass of the substances involved in a chemical change. 21

22 sodium + sulfur sodium sulfide 46.0 g 32.1 g 78.1 g 78.1 g reactant mass of reactants = 78.1 g product mass of products This is the Law of Conservation of Mass: In a chemical reaction, mass is neither created nor destroyed. 22

23 Heat Energy and the Specific Heat of a Substance 23

24 The specific heat of a substance is the quantity of heat required to change the temperature of 1 g of that substance by 1 o C. 24

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26 The units of specific heat in joules are: Joules o gram Celcius J gc o 26

27 The units of specific heat in calories are: calories o gram Celcius cal gc o 27

28 The relation of mass, specific heat, temperature change (Δt), and quantity of heat lost or gained is expressed by the general equation: specific heat = mass heat q = mcdt temperature change (t f - t o ) 28

29 Heat q = mcdt Where: m = mass (in g) C = Specific Heat Capacity (in J/g C) DT = T f - T o (in C) 29

30 Question How much heat (q) is required to raise the temperature of 1.00 g of water from 25 C to 75 C? The specific heat of water is J/g C. 30

31 Answer m = 1.00 g c = J/g C DT = (T f T i ) = = 50. C q = mcdt = (1.00 g)(4.184 J/g C)(50. C) q = 210 J 31

32 A Clicker Question How much heat (q) is required to raise the temperature of 1.00 g of water from 25.0 C to 100. C? The specific heat of water is J/g C. 71% J J J J 17% 8% 4% t, w1 &w2

33 Answer m = 1.00 g c = J/g C DT = (T f T i ) = = 75. C q = mcdt = (1.00 g)(4.184 J/g C)(75. C) q = 310 J 33

34 evaporation q = mc Heat flow that condensation produces a phase change w/o a temperature change (i.e. B-C and D-E). q = mcdt Heat flow that produces a temperature change w/o a phase change (i.e. A-B,C-D and E-F). melting freezing 13.5 Heating curve for a pure substance. 34

35 Latent Heat is the heat energy involved in a phase change with no accompanying change in temperature. q = mc Where: m = mass (g) C = Heat of Fusion (J/g) 35

36 How many joules of energy are needed to change 10.0 g of ice at 0.00 o C to water 20.0 o C? Determine the joules necessary to melt 10.0 g of ice. The heat of fusion of ice at 0 o C is 335 J/g. q = mc 10.0 g 335 J 1 g = x 10 J 36

37 How many joules of energy are needed to change 10.0 g of ice at 0.00 o C to water 20.0 o C? Next, determine the joules necessary to heat 10.0 g of water from 0.00 o C to 20.0 o C; q = mcdt. The specific heat of water is J/g o C J 10.0 g o 20.0 o C = 1 g C The total heat absorbed by the system is the heat required to melt the ice plus the heat required to raise the water temperature from 0.00 o C to 20 o C. q = 3350 J J = 4.19 x 10 3 J 837 J 37

38 Energy in Chemical Changes 38

39 In all chemical reactions, matter either absorbs energy( referred to as Endothermic reactions) or releases energy( referred to as Exothermic reactions). 39

40 Examples of Heat Energy in Chemical Reactions Endothermic Reaction: N 2 + O 2 + Heat 2NO (heat is a reactant) Exothermic Reaction: CH 4 + 2O 2 2H 2 O + CO 2 + Heat (heat is a product) 40

41 Conservation of Energy 41

42 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 (e.g. heat to potential energy or visa versa). 42

43 An energy transformation occurs whenever a chemical change occurs. If energy is absorbed during a chemical change, the products will have more potential energy than the reactants. This is an endothermic reaction. If energy is released in a chemical change, the products will have less potential energy than the reactants. This is an exothermic reaction. 43

44 H 2 + O 2 have higher potential energy than H 2 O higher energy potential is absorbed energy lower energy potential is given energy off Endothermic Reaction Exothermic Reaction Electrolysis of Water Burning of Hydrogen in Air 4.4 The difference in potential energies between the reactants and the products is heat (i.e. enthalpy). 44

45 A Clicker Question CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) KJ Is this reaction Exothermic or Endothermic and is the PE of the products higher or lower than the PE of the reactants? 46% 1. Endothermic, Higher 2. Exothermic, Lower 3. Endothermic, Lower 4. Exothermic, Higher 20% 4% 30%

46 Answer CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) KJ Heat is a product, so heat is being released and the PE of the products will be lower than the PE of the reactants KJ 46

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