Chapter 3 Matter, Changes and Energy
Formulating some questions What are the most basic forms of matter? What are the criteria that allow us to distinguish one substance from another? How do we describe mixtures of substances? How does energy relate to changes in matter? 2
Chapter 3 Objectives OBJECT I VE S Section You Should be able to Examples Exercises 3-1 List and define several properties of matter and distinguish them as physical or chemical. 3-2 Perform calculations involving the density of liquids and solids. 3-3 Describe the differences in properties between a pure substance and a mixture. Perform calculations involving percent as applies to mixtures. 3-4 Distinguish among the forms and types of energy. Define the terms endothermic and exothermic, providing several examples of each type of process. 3-5 Perform calculations involving the specific heat of a substance, and use them to identify a substance. 3-1, 3-2, 3-3, 3-4 Chapter Problems 1a, 1b, 1c 4, 5, 6, 9, 11 2a, 2b, 2c 12, 14, 16, 20, 22, 24, 28, 29 3a, 3b, 3c, 3d 41, 42, 48, 49 3-5, 3-6 3e, 3f, 3g 50, 52, 53, 55 3-7, 3-8, 3-9, 3-10 4b, 4c 57, 59, 60 4a 56 5a, 5b, 5c, 5d, 5e, 5f 63, 64, 67, 68, 69, 71, 79, 81 3
Questions for you more familiar material Choose the best answer describing the properties characteristic of a solid a) lacks a definite shape b) lacks a definite volume c) has a definite shape and volume d) has a definite volume The temperature at which a liquid changes into a gas is the a) melting point b) condensation point c) boiling point d) freezing point Choose the intensive (vs extensive) property: (extensive prop changes with amt, intensive does not) a) color b) mass c) volume d) conductivity Chemical changes a) Convert one substance into one or more other substances b) Convert a liquid into a gas c) Lower the density of a substance d) Convert a solid directly to a gas 4
Chemistry (Quick Review) Chemistry - study of matter and the changes it undergoes Matter - anything that has mass and occupies space Law of the Conservation of Mass - matter is neither created nor destroyed in chemical reactions Universe also contains energy 5
Types of matter - Elements The most basic form of matter under ordinary circumstances Simplest chemical substance Only a few elements are found in their free state (nitrogen, oxygen, gold, etc.) Learn elements 1-36 6
Compounds A unique substance composed of two or more elements that are chemically combined (i.e. joined intimately, not just mixed together) also, molecular vs ionic Compounds include substances like water, table salt, sugar Pure compounds have definite compositions and properties (e.g. water, ethylene glycol) Require complex chemical procedures to separate into simpler substances (elements) 7
Properties of substances Properties describe the particular characteristics of a substance Pure substances have definite composition and definite, unchanging properties the properties of mixtures can change Physical properties - can be observed without changing the identity of a substance (BP, FP, gas, liquid, solid, etc) Chemical properties - require that the substance change into another (A reacts with B to always from C, etc) 8
Physical states The three physical states are solid, liquid and gas solids - have a definite shape and volume liquid - have a definite volume but not a definite shape gas - neither a definite volume or shape A substance exists in a particular physical state under defined conditions temperature and pressure (phase diagram H 2 O) (phase diagram CO 2 ) 9
Phase changes (physical properties) Melting point or freezing point temperature at which a substance changes from solid to liquid Boiling point or condensation point temperature at which a substance changes from liquid to gas (Normal bp and fp!) Look again at water (phase diagram H 2 O) 10
Chemical properties Chemical properties - involve how a substance changes into another using a reaction or heat Sometimes quite difficult to determine Some examples are burning (as opposed to boiling) and color changes 11
Questions for you less familiar Choose the substance with the greatest density (all densities in g/ml). a) Ethyl alcohol density = 0.79 b) Gold density = 19.3 c) Table salt density = 2.16 d) Lithium density = 0.53 What is the volume in ml of 77.8 g of table salt? a) 98.5 ml b) 4.03 ml c) 36.0 ml d) 147 ml Choose the heterogeneous mixture. a) milk b) Gatorade c) sterling silver d) tap water Choose the endothermic process. a) photosynthesis of carbohydrates by plants b) burning of gasoline in a car c) rusting of iron d) butter turning rancid Choose the correct definition of a nutritional calorie. a) amount of heat required to raise one gram of water one degree Celcius b) 4.184 J c) 10.0 cal d) 1 kcal 12
Density (a physical property) ratio of the mass of a substance to the volume of that mass g/ml Units usually g/ml for solids and liquids, (water = 1.0 g/ml); g/l for gases also a conversion factor relating the mass of a substance to its volume WORK PROBLEMS (13, 15, 20, 22) Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water, e.g. 1.10 g/ml/1.0 g/ml = 1.1 S.G. 13
Energy changes Energy is the capacity to do work Many forms of energy heat light chemical (stored energy) electrical energy mechanical nuclear 14
Energy Law of the Conservation of Energy - energy cannot be created or destroyed, but only transformed from one form to another The transformation from one type to another may not be efficient (the efficiency of transforming sunlight to electricity is only about 35% efficient. The other 65% is lost as heat.) 15
Energy flow Kinetic energy - energy resulting from motion Potential energy is energy (potentially) available due to position or composition Exothermic reactions - produce energy (release energy to the surroundings) Endothermic reactions - require energy (store energy) 16
Temperature and specific heat Recall that we measure temperature in C or K Energy units calorie (cal) - amount of heat required to raise the temperature of one gram of water from 14.5 C to 15.5 C (1 g 1 degree) joule - 1 cal = 4.184 J (definition so exactly) Nutritional calorie is actually 1000 (thermochemical) cal (indicated as 1 C but really 1 kcal in most fields other than nutrition) 17
Specific Heat (A Physical Property of a Material) Specific heat - the amount of heat required to raise the temperature of one gram of a substance one degree Celsius (or Kelvin) Reflects how some substances heat up faster than others amount of heat (cal or J) = Sp.ht X mass X DT (Problems 63, 64, 69-70) 18
Heat flow When two substances at different temperatures are in contact, or mixed, heat flows from the substance at higher temperature to the substance at lower temperature This heat flow continues until the temperatures are the same Temperature change depends on heat capacity (Demo) 19
Specific Heat (A Physical Property of a Material) Specific heat - the amount of heat required to raise the temperature of one gram of a substance one degree Celsius (or Kelvin) Reflects how some substances heat up faster than others (Problems) 63, 64, 69, 70 20
Mixtures Combinations of two or more substances Can be separated by physical means (filtration, distillation, crystallization, chromatography) Have chemical and physical properties that are different from the pure substances that make them up 21
Types of Mixtures Heterogeneous mixture - nonuniform mixture containing two or more phases with definite boundaries between the phases (e.g. ice and water) Phase - one physical state with distinct boundaries and uniform properties Homogeneous mixture - same throughout and contains only one phase (substances are mixed at the atomic or molecular level) 22
Solutions A type of homogeneous mixture, we will use often Usually involves a liquid phase, but can be solid-solid, liquid-liquid, solid-liquid, etc. The pure substances can be in different phases but form a homogeneous mixture (table salt and water, for example) 23
Alloys important solid solutions of two or more metals (Alloys blend properties of the components to give desired physical property) dental fillings (silver and mercury) stainless steel (iron, chromium and nickel) 24
Percent by mass (or, volume) Mass of specific material (unit) Mass of specific material (unit) X 100% = 20 grams of NaCl is dissolved in 80 grams of water. What is the concentration of the solution in percent by mass? If I have a solution that is 43% by mass NaCl in water, how many grams of NaCl are in 25 g of solution? 25