CHAPTER 4: MATTER & ENERGY

Transcription

1 CHAPTER 4: MATTER & ENERGY Problems: 1,3,5,7,13,17,19,21,23,25,27,29,31,33,37,41,43,45,47,49,51,53,55,57,59,63,65,67,69,77,79,81, Physical States of Matter Matter: Anything that has mass and occupies space. Matter exists in one of three physical states: solid, liquid, or gas. (See Fig. 4.1 below.) gas: Particles are far apart and are in constant random motion.! Gases assume the shape of the container.! Volume is variable (changeable): If volume increases, particles move apart to fill entire container. If volume decreases, particles move closer together. liquid: Particles are close together but are free to move past one another.! Liquids assume the shape of the container.! Volume is constant (can t compress). solid: Particles are packed tightly together; these particles vibrate but remain in their place.! Solids have a definite, fixed shape.! Volume is constant. Know the terms shown below for changes in physical state! Fig. 4.1 from Corwin on p. 74 CHM 130: Corwin Chapter 4 page 1 of 8

2 4.2 Elements, Compounds, and Mixtures pure substance: consist of a single chemical with a fixed composition and distinct properties. A pure substance cannot be separated into parts by physical means. Two types of pure substances: element:! consist of only one type of atom! a substance that cannot be broken down further by chemical reaction e.g. carbon (C), hydrogen (H 2 ), sulfur (S 8 ), copper wire (Cu) compound! consist of two or more elements and has a specific formula! a substance that can be chemically separated into its elements e.g. ethanol (C 2 H 5 OH) can be broken down to C, H, & O Two or more pure substances can combine physically to form mixtures. mixture! consist of two or more compounds and/or elements, but has no specific formula! has variable composition with definite or varying properties! a mixture can be physically separated into its component elements and/or compounds e.g. Metal alloys like 10-K to 18-K gold; coarse mixtures like sea water or sand; gas mixtures like air which consists of nitrogen, oxygen, and other trace gases. Note: You do not need to distinguish between homogeneous or heterogeneous mixtures as categorized in the book! Molecular-level Images: represent substances as atoms and molecules An element A compound A mixture CHM 130: Corwin Chapter 4 page 2 of 8

3 A D B E C F Ex. 1: 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: B: C: D: E: F: 4.3 Names and Symbols of the Elements Each element has a unique name, symbol, and number. Convention for writing chemical symbols Capitalize first letter of element name: hydrogen H, carbon C If the letter is already used, include the second letter (in lower case) of the name: helium He, calcium Ca, cobalt Co Note: Some symbols come from Latin names: e.g. lead is Pb = plumbum gold is Au = aurum (which means golden dawn ) KNOW THE NAMES AND SYMBOLS OF THE FIRST EIGHTEEN ELEMENTS OF THE PERIODIC TABLE & THE FOLLOWING Ag silver Au gold Pb lead Br Bromine I iodine Hg mercury (There will be a few more later this semester.) CHM 130: Corwin Chapter 4 page 3 of 8

4 4.4 Metals, Nonmetals, and Semimetals Properties of Metals vs. Nonmetals Metals shiny appearance Malleable, ductile density usually high Good conductors of heat & electricity Nonmetals dull appearance brittle density usually low Poor conductors (make better insulators) semimetals: Have properties intermediate between metals and nonmetals. e.g. silicon Location of nonmetals, semimetals, metals on the Periodic Table (Fig. 4.5 on p. 81)! Nonmetals (except H) are located on the top-right of the Periodic Table! Semimetals are along the stair-step following B (except Al)! All remaining elements are metals Know if an element is a metal, nonmetal, or semimetal based on its position in the Periodic Table! Physical States of the Elements at 25 C and normal atmospheric pressure Normal Physical State of the Elements: (Figure 4.6 on p. 82)! Only mercury (Hg) and bromine (Br 2 ) are liquids! H 2, N 2, F 2, O 2, Cl 2, and all Noble gases (Group VIIIA) are gases! All other elements are solids Know if an element is a solid, liquid, or gas given only the Periodic Table! 4.5 Compounds and Chemical Formulas atom: smallest unit particle of an element that retains the chemical identity of the element. molecule: composed of two or more nonmetal atoms bonded together. Many elements exist as diatomic molecules: H 2, N 2, F 2, O 2, I 2, Cl 2, Br 2 chemical formula:! expresses the type and number of atoms present in a compound! number of atoms is indicated by a subscript following the element s symbol (If there is no subscript, only one atom of that element is in the compound.) Example: water = H 2 O 2 H atoms, 1 O atom sodium sulfate = Na 2 SO 4 Na, S, O atoms! Parentheses are used when there is more than one subunit present in the compound. Example: (NH 4 ) 2 CO 3 (NH 4 ) 2 = 2 NH 4 s = 2 N + 2 (4 H) = 8 H TOTAL: 2 N, 8H, 1 C and 3 O CHM 130: Corwin Chapter 4 page 4 of 8

5 Example. How many atoms of each element are present in TNT: C 7 H 5 (NO 2 ) 3? C, H, N, and O Law of Definite (or Constant) Composition: Compounds always contain the same elements in the same proportion by mass. e.g. Water always contains 11.2% hydrogen and 88.8% oxygen by mass. 4.6 Physical and Chemical Properties Physical Properties: inherent characteristics of a substance observable without changing the substance chemically. Examples include: physical state (solid, liquid, gas) electrical & heat conductivity color solubility density hardness melting and boiling points odor Chemical Properties: describe how a substance reacts with other substances e.g. hydrogen reacts explosively with oxygen, iron rusts slowly in air 4.7 Physical and Chemical Changes physical change: a process that does not alter the chemical composition of the substance substance only changes its physical state or shape or form e.g. boiling water, melting gold, breaking glass, dissolving salt in water Note that the H 2 O molecules in Fig (p. 95) remain H 2 O regardless of whether the sample is a solid, liquid, or gas; thus, changes in physical state are physical changes. chemical change: a process that changes the chemical composition of the substance Starting substance is destroyed and a new substance with different properties is formed. Indicators of chemical change: oxidation of matter (burning or rusting) release of gas bubbles (fizzing) formation of insoluble solid (precipitation) release of heat or light change in color or odor. CHM 130: Corwin Chapter 4 page 5 of 8

6 e.g. Hydrogen gas (H 2 ) reacts with oxygen gas (O 2 ) to produce water. This is a chemical change since the starting materials are different from the substance produced. chemical equation - describes a chemical change Form of chemical equation: REACTANTS PRODUCTS Starting substances on left are called reactants; New substances formed on right are called products. E.g. 2 H 2 + O 2 2 H 2 O 4.8 Conservation of Mass Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction. Mass of the reactant(s) = mass of the product(s). For example: 11.2 g hydrogen g oxygen = g water Ex. 1: A 150.0g sample of potassium iodide contains g of iodine. Determine the mass of potassium in the sample. Ex. 2: Methane burns by reacting with oxygen present in air to produce steam and carbon dioxide gas. Calculate the mass of oxygen that reacts if 50.0 g of methane produces g of steam and g of carbon dioxide. 4.9 Potential and Kinetic Energy kinetic energy (KE): energy resulting from motion e.g. water flowing over dam, working out, dancing, burning gasoline potential energy (PE): stored energy that matter possesses due to its position or its chemical bonds. e.g. water stored in dam, gasoline and other fuels, food Kinetic Energy, Temperature, and Physical States As temperature increases, the particles move faster Solids have lowest KE! Strongest attraction between particles particles vibrate in fixed positions If heated enough, particles gain enough energy to break out of their positions the solid begins to melt and become a liquid CHM 130: Corwin Chapter 4 page 6 of 8

7 Liquids have slightly higher KE! Particles are still attracted to each other but can move past one another particles are less restricted If heated enough, particles gain enough energy to completely break away from one another the liquid begins to evaporate and become a gas. Gases have greatest KE! Attractive forces almost (if not) completely overcome, so particles can fly freely within container particles are completely unrestricted 4.10 Conservation of Energy Law of Conservation of Energy (E): Energy can neither be created nor destroyed Total E of the reactant(s) of a reaction must = total E of the product(s). Energy and Physical Changes Note that the amount of energy used to change a solid to liquid is the same amount of energy released when the same sample of liquid freezes Given the following: A 1.00 g sample of water requires 540 calories of heat to be converted to steam: 1.00 g water calories 1.00 g steam Fill in the blanks below: 1.00 g steam 1.00 g water g water g steam Energy and Chemical Changes Energy can also be used for to bring about chemical changes For example: water + electrical energy hydrogen gas + oxygen gas The law of conservation of energy still applies, so hydrogen gas + oxygen gas water + electrical energy Note that these reactions show how hydrogen gas can be produced from water, then how hydrogen can react with oxygen in air to produce energy. Forms of Energy: Six types of energy: heat, light, chemical, electrical, mechanical, and nuclear each can be converted to another CHM 130: Corwin Chapter 4 page 7 of 8

8 Identify at least two types of energy involved for each of the following: 1. When you turn on a lamp? and 2. When you turn on a radio? and 3. When you use your cell phone? and 4. With solar panels? and Law of Conservation of Mass & Energy: Total of mass + energy of reactants must = Total of mass + energy of products. Some mass may actually be converted to energy, but the total must remain the same. Einstein s equation: E=mc 2 (c = speed of light = m/s) A very small amount of mass enormous amount of Energy! This is the basis for the atomic bomb and nuclear power plants. CHM 130: Corwin Chapter 4 page 8 of 8