CHAPTER 3: MATTER & ENERGY

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1 CHAPTER 3: MATTER & ENERGY Problems: 1-50, 57-58, 61-74, 107, What is Matter? Matter: Anything that has mass and occupies volume We study matter at different levels: macroscopic: the level that can be observed with the naked eye e.g. geologists study rocks and stone at the macroscopic level microscopic: the level that can be observed with a microscope e.g. scientists study tiny animals, plants, or crystals at microscopic level particulate: at the level of atoms and molecules, also called atomic or molecular level cannot be observed directly even with the most powerful microscopes where the term nanotechnology comes from since many atoms and molecules are about a few nanometers in size Substances like water can be represented using different symbols (e.g H 2 O) and models. CHEM 121: Tro Chapter 3 page 1 of 13

2 3.3 Classifying Matter According to Its State: Solid, Liquid, and Gas Matter exists in one of three physical states: solid, liquid, gas solid: Has definite shape and a fixed (or constant) and rigid volume Particles only vibrate in place. liquid: Has a fixed (or constant) volume, but its shape can change. Takes the shape of its container because particles are moving Particles are packed closely together but can move around each other. gas: Volume is variable, and particles are far apart from one another. Takes the shape of the container because particles are moving If container volume expands, particles move apart to fill container. If container volume decreases, particles move closer together. Gases are compressible i.e., can be forced to occupy a smaller volume. Particles are in constant random motion. CHEM 121: Tro Chapter 3 page 2 of 13

3 3.4 Classifying Matter According to Its Composition: Elements, Compounds, and Mixtures We can classify matter into pure substances and mixtures: pure substance: a single chemical, consisting of only one kind of matter There are two types of pure substances: elements and compounds. In the figure below, copper rods are an example of an element, and sugar is an example of a compound. mixture: consists of two or more elements and/or compounds Mixtures can be homogeneous or heterogeneous: Homogeneous mixtures have a uniform appearance and composition because the particles in them mix uniformly (e.g. solutions like sweetened tea below) Heterogeneous mixtures do not have a uniform composition. e.g. chocolate chip cookie, water and C 8 H 18 mixture below shown as separate layers CHEM 121: Tro Chapter 3 page 3 of 13

4 elements: consist of only one type of atom atoms cannot be broken down into smaller components by chemical reaction e.g. copper wire (Cu), sulfur powder (S 8 ) Examples also include sodium (Na), barium (Ba), hydrogen gas (H 2 ), oxygen gas (O 2 ), and chlorine gas (H 2 ). compounds: consist of more than one type of atom and have a specific chemical formula Examples include hydrogen chloride (HCl), water (H 2 O), sodium chloride (NaCl) which is table salt, barium chloride (BaCl 2 ) Two or more pure substances combine to form mixtures. mixtures: consist of many compounds and/or elements, with no specific formula Matter having variable composition with definite or varying properties can be separated into component elements and/or compounds e.g., any alloy like brass, steel, 10K to 18K gold; sea water, carbonated soda; air consists of nitrogen, oxygen, and other trace gases. The image at the right shows that air is a mixture of mostly nitrogen (N 2 in blue) and some oxygen (O 2 in red) while salt water consists of salt (Na + and Cl - ions or charged particles) dissolved in water. Example: Is salt water a homogeneous or heterogeneous mixture? Explain. CHEM 121: Tro Chapter 3 page 4 of 13

5 3.5 How We Tell Different Kinds of Matter Apart: Physical and Chemical Properties The characteristics that distinguish one substance from another are called properties. Physical Properties: inherent characteristics of a substance independent of other substances physical state (solid, liquid, gas) electrical & heat conductivity color odor density hardness melting and boiling points solubility (does/does not dissolve in water) Chemical Properties: how a substance reacts with other substances e.g. hydrogen reacts explosively with oxygen 3.6 How Matter Changes: Physical and Chemical Changes physical change: a process that does not alter the chemical makeup of the starting materials Note in the figure below that the H 2 O molecules remain H 2 O regardless of the physical state (solid, liquid, or gas). Changes in physical state are physical changes. Other examples of physical changes include hammering gold into foil, dry ice subliming Dissolving table salt or sugar in water is also a physical change. A substance dissolved in water is the fourth physical state, aqueous. CHEM 121: Tro Chapter 3 page 5 of 13

6 Know the terms for transitions from one physical state to another: freezing: liquid solid condensing: gas liquid melting: solid liquid evaporating (or vaporizing): liquid gas Two less common transitions: sublimation: solid gas (e.g. dry ice sublimes) deposition: gas solid (e.g. water vapor deposits on an icebox) chemical change: a process that does change the chemical makeup of the starting materials We can show H 2 and O 2 reacting to form water (H 2 O) below. Since the H 2 O has a different chemical makeup than H 2 and O 2, this is a chemical change. Other examples of chemical changes: e.g. oxidation of matter (burning or rusting), release of gas bubbles (fizzing), mixing two solutions to form an insoluble solid (precipitation), and other evidence indicating the starting materials (reactants) were changed to a different substance. The following examples are all chemical changes that convert the reactants to completely different compounds and/or elements. release of gas bubbles (fizzing) formation of insoluble solid (precipitation) oxidation (burning or rusting) CHEM 121: Tro Chapter 3 page 6 of 13

7 Example 1: Consider the following molecular-level representations of different substances: A D B E C F For each figure above, indicate if it represents an element, a compound, or a mixture AND if it represents a solid, liquid, or gas. A: element compound mixture solid liquid gas B: element compound mixture solid liquid gas C: element compound mixture solid liquid gas D: element compound mixture solid liquid gas E: element compound mixture solid liquid gas F: element compound mixture solid liquid gas Ex. 2: Circle all of the following that are chemical changes: burning condensing dissolving rusting vaporizing precipitating CHEM 121: Tro Chapter 3 page 7 of 13

8 3.7 Conservation of Mass: There is No New Matter Chemical Reaction: REACTANTS PRODUCTS (starting materials) (substances after reaction) For the reaction: C + O 2 CO 2 The reactants are carbon and oxygen gas, and the product is carbon dioxide. Antoine Lavoisier ( ), a French chemist, carried out experiments on combustion by burning different substances and measuring their masses before and after burning. He found that there was no change in the overall mass of the sample and air around it. Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction, so mass is conserved. Mass of the product(s) in a reaction must be equal to the mass of the reactant(s). For example: 11.2 g hydrogen g oxygen = g water Ex. 1: Methane burns by reacting with oxygen present in air to produce steam and carbon dioxide gas. Calculate the mass of oxygen that reacts if burning 50.0 g of methane produces g of steam and g of carbon dioxide. 3.8 Energy: the capacity to do work potential energy (PE): energy due to position or its composition (chemical bonds) A 10-lb bowling ball has higher PE when it is 10 feet off the ground compared to 10 inches off the ground Greater damage on your foot after falling 10 feet compared to falling only 10 inches In terms of chemical bonds, the stronger the bond, more energy is required to break the bond, the higher the potential energy of the bond CHEM 121: Tro Chapter 3 page 8 of 13

9 kinetic energy (KE): energy associated with an object s motion e.g. a car moving at 75 mph has much greater KE than the same car moving at 15 mph Greater damage if the car crashes at 75 mph than at 15 mph Six Forms of Energy: heat, light, chemical, electrical, mechanical, and nuclear Each can be converted to another. Example: Identify at least two types of energy involved for each of the following: 1. When you turn on a lamp 2. When using solar panels 3. At the Springfield Power Plant in The Simpsons Energy changes accompany physical and chemical changes due to changes in potential and kinetic energy. Kinetic Energy and Physical States Solids have the lowest KE of the three physical states Highest attraction between particles particles are fixed Liquids have slightly higher KE than solids Particles are still attracted to each other but can move past one another particles are less restricted Gases have greatest KE compared to solids and liquids Attractive forces completely overcome, so particles fly freely within container particles are completely unrestricted CHEM 121: Tro Chapter 3 page 9 of 13

10 3.10 Temperature: Random Molecular and Atomic Motion Heat: Energy that is transferred from a body at a higher temperature to one at a lower temperature heat always transfers from the hotter to the cooler object! "heat flow" means heat transfer Heat Transfer and Temperature One becomes hotter by gaining heat. One becomes colder by losing heat i.e., when you feel cold, you are actually losing heat! Ex. 1: Fill in the blanks to indicate how heat is transferred: a. You burn your hand on a hot frying pan. loses heat, and gains the heat. b. Your tongue feels cold when you eat ice cream. loses heat, and gains the heat. Ex. 2: A small chunk of gold is heated in beaker #1, which contains boiling water. The gold chunk is then transferred to beaker #2, which contains room-temperature water. a. The temperature of the water in beaker #2. stays the same b. Fill in the blanks: loses heat, and gains the heat. Ex. 3: Why do surfaces like a stone countertop or metal flatware (forks, knives, etc.) feel cold in restaurant? Aren t they at room temperature like you? Explain. 3.9 Energy and Chemical and Physical Change endothermic change: a physical or chemical change that requires energy or heat to occur boiling water requires energy: H 2 O(l) + heat energy H 2 O(g) electrolysis of water requires energy: 2 H 2 O(l) + electrical energy 2 H 2 (g) + O 2 (g) exothermic change: a physical or chemical change that releases energy or heat water condensing releases energy: H 2 O(g) H 2 O(l) + heat energy hydrogen burning releases energy: 2 H 2 (g) + O 2 (g) 2 H 2 O(g) + heat energy CHEM 121: Tro Chapter 3 page 10 of 13

11 For physical changes, consider whether the reactants or products have more kinetic energy. If the reactants have greater kinetic energy than the products exothermic process. If the products have greater kinetic energy than the reactants endothermic process. system: that part of the universe being studied surroundings: the rest of the universe outside the system For chemical changes, observe if the surroundings (including you) feel hotter or colder after the reaction has occurred. If the surroundings are hotter, the reaction released heat exothermic reaction. If the surroundings are colder, the reaction absorbed heat endothermic reaction. Ex. 1: Circle all of the following changes that are exothermic: freezing vaporizing sublimation melting deposition CHEM 121: Tro Chapter 3 page 11 of 13

12 Ex. 2: A student adds ammonium chloride (NH 4 Cl) salt to a test tube containing water and notices that the test tube feels colder as the ammonium chloride dissolves. Is this process exothermic or endothermic? Explain. Ex. 3: A student mixes two solutions, hydrochloric acid and sodium hydroxide, and notices the beaker with the substances feels hotter as they mix. Is this reaction exothermic or endothermic? Explain. Units of Energy calorie (cal): unit of energy used most often in the US amount of energy required to raise the temperature of 1 g of water by 1 C 1 cal J (Note: This is EXACT!) But a nutritional calorie (abbreviated Cal) is actually 1000 cal: 1 Cal = 1 kcal = kj joule (J): SI unit of energy J To recognize the size of a joule, note that 1 watt = 1 s So a 100-watt light bulb uses 100 J every second. Heat is also often reported in kilojoules (kj), where 1 kj = 1000 J Electricity usage on our electricity bills are generally reported in kilowatt-hour (kwh). Example: A 100 W lightbulb running for 10.0 hours requires 1 kwh of energy. If the average Seattle home uses 25 kwh/day, this is equal to how many 100 W light bulbs running nonstop for one day? CHEM 121: Tro Chapter 3 page 12 of 13

13 Energy and Food Values food value: The amount of heat released when food is burned completely, usually reported in kj/g food or Cal/g food. Most of the energy needed by our bodies comes from carbohydrates and fats, and the carbohydrates decompose in the intestines into glucose, C 6 H 12 O 6. The combustion of glucose produces energy that is quickly supplied to the body: C 6 H 12 O 6 (g) + 6 O 2 (g) 6 CO 2 (g) + 6 H 2 O(g) + heat energy The body also produces energy from proteins and fats, which can be stored because fats are insoluble in water and produce more energy than proteins and carbohydrates. The energy content reported on food labels is generally determined using a bomb calorimeter similar to that described in the previous section Temperature Changes: Heat Capacity heat capacity: amount of heat necessary to raise the temperature of a given amount of any substance by 1 C; in units of J/ C specific heat capacity: amount of heat necessary to raise the temperature of 1 gram of any (or specific heat) substance by 1 C; has units of J/g C Water has a relatively high specific heat (4.184 J/g C) compared to the specific heats of rocks and other solids (1.3 J/g C for dry Earth, 0.9 J/g C for concrete, 0.46 J/g C for iron) Example: Water covers most of the Earth. Compare the specific heat of water with Earth and other solids given above, then explain what would happen if the Earth were covered mostly in land not water. CHEM 121: Tro Chapter 3 page 13 of 13