Chapter 4 Matter and Energy Vanessa N. Prasad-Permaul CHM 1025 Valencia Community College
Matter • Matter is any substance that has mass and occupies volume. • Matter exists in one of three physical states: • Solid • Liquid • Gas
Gaseous State • In a gas, the particles of matter are far apart and uniformly distributed throughout the container. • Gases have an indefinite shape and assume the shape of their container. • Gases can be compressed and have an indefinite volume. • Gases have the most energy of the three states of matter.
Liquid State • In a liquid, the particles of matter are loosely packed and are free to move past one another. • Liquids have an indefinite shape and assume the shape of their container. • Liquids cannot be compressed and have a definite volume. • Liquids have less energy than gases, but more energy than solids.
Solid State • In a solid, the particles of matter are tightly packed together. • Solids have a definite, fixed shape. • Solids cannot be compressed and have a definite volume. • Solids have the least energy of the three states of matter.
Changes in Physical States • Most substances can exist as either a solid, a liquid, or a gas. • Water exists as a solid below 0 °C; as a liquid between 0 °C and 100 °C; and as a gas above 100 °C. • A substance can change physical states as the temperature changes.
Solid ↔ Liquid Phase Changes • When a solid changes to a liquid, the phase change is called melting. • A substance melts as the temperature increases. • When a liquid changes to a solid, the phase change is called freezing. • A substance freezes as the temperature decreases.
Liquid ↔ Gas Phase Changes • When a liquid changes to a gas, the phase change is called vaporization. • A substance vaporizes as the temperature increases. • When a gas changes to a liquid, the phase change is called condensation. • A substance condenses as the temperature decreases.
Solid ↔ Gas Phase Changes • When a solid changes directly to a gas, the phase change is called sublimation. • A substance sublimes as the temperature increases. • When a gas changes directly to a solid, the phase change is called deposition. • A substance undergoes deposition as the temperature decreases.
EXAMPLE 4.1Change of Physical State State the term that applies to each of the following changes of physical state: (a) Snow changes from a solid to a liquid. (b) Gasoline changes from a liquid to a gas. (c) Dry ice changes from a solid to a gas. Solution Refer to Figure 4.1 for the changes of physical state. (a) The change from solid to liquid is called melting. (b) The change from liquid to gas is called vaporizing. (c) The change from solid to gas is called sublimation. Figure 4.1 Changes in Physical State As temperature increases, a solid melts to a liquid and then vaporizes into a gas. As temperature decreases, a gas condenses to a liquid and then freezes to a solid.
EXERCISE 4.1 Change of Physical State Practice Exercise State the term that applies to each of the following changes of physical state: (a) A refrigerant changes from a gas to a liquid. (b) Water changes from a liquid to a solid. (c) Iodine vapor changes from a gas to a solid. Figure 4.1 Changes in Physical State As temperature increases, a solid melts to a liquid and then vaporizes into a gas. As temperature decreases, a gas condenses to a liquid and then freezes to a solid.
Concept Exercise Identify the physical state (solid, liquid, gas) that corresponds to each of the following pictorial representations: EXERCISE 4.1 Change of Physical State
Classifications of Matter • Matter can be divided into two classes: • Mixtures • Pure substances • Mixtures are composed of more than one substance and can be physically separated into its component substances. • Pure substances are composed of only one substance and cannot be physically separated.
Mixtures • There are two types of mixtures: • Homogeneous mixtures • Heterogeneous mixtures • Homogeneous mixtures have uniform properties throughout. • Salt water is a homogeneous mixture. • Heterogeneous mixtures do not have uniform properties throughout. • Sand and water is a heterogeneous mixture.
Pure Substances • There are two types of pure substances: • Compounds • Elements • Compounds can be chemically separated into individual elements. • Water is a compound that can be separated into hydrogen and oxygen. • An element cannot be broken down further by chemical reactions.
EXAMPLE 4.2Element, Compound, or Mixture Consider the following properties of the element copper: (a) Copper metal cannot be broken down by a chemical change. (b) Copper reacts with oxygen in air to give copper oxide. (c) Copper, in the form of malachite ore, is found worldwide. (d) Copper and tin compose bronze alloy. Classify each of the following copper samples as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: (a) copper wire (b) copper oxide (c) malachite ore (d) bronze alloy Solution Refer to Figure 4.2 to classify each sample. (a) Copper wire is a metallic element. (b) Copper oxide is a compound of the elements copper and oxygen. (c) Malachite ore is a heterogeneous mixture of copper and other substances. (d) Bronze alloy is a homogeneous mixture of copper and tin. Figure 4.2 Classification of Matter Matter may be either a mixture or a pure substance. The properties of a heterogeneous mixture vary within the sample (oil and water). The properties of a homogeneous mixture are constant (salt solution). A pure substance may be either a compound (water) or an element (gold). Left to right: oil and water; NaCl solution; H2O; and gold nugget.
EXERCISE 4.2 Element, Compound, or Mixture Practice Exercise Consider the following properties of the element mercury: (a) Mercury liquid cannot be broken down by a chemical change. (b) Mercury oxide can be heated to give mercury and oxygen gas. (c) Mercury, in the form of cinnabar ore, is found in Spain and Italy. (d) Mercury and silver compose the alloy used for dental fillings. Classify each of the following mercury samples as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: (a) mercury liquid (b) mercury oxide (c) cinnabar ore (d) dental alloy
EXERCISE 4.2 Element, Compound, or Mixture Concept Exercise Classify each of the following as an element, a compound, or a mixture as shown in the illustration:
Occurrence of the Elements • There are over 100 elements that occur in nature; 81 of those elements are stable. • Only 10 elements account for 95% of the mass of Earth’s crust:
Elements in the Human Body • Oxygen is the most common element in Earth’s crust and in the human body. • While silicon is the second most abundant element in Earth’s crust, carbon is the second most abundant in the body.
Names of the Elements • Each element has a unique name. • Names have several origins: • Hydrogen is derived from Greek. • Carbon is derived from Latin. • Scandium is named for Scandinavia. • Nobelium is named for Alfred Nobel. • Yttrium is named for the town of Ytterby, Sweden.
Element Symbols • Each element is abbreviated using a chemical symbol. • The symbols are one or two letters long. • Most of the time, the symbol is derived from the name of the element. • C is the symbol for carbon. • Cd is the symbol for cadmium. • When a symbol has two letters, the first is capitalized and the second is lowercase.
Other Element Symbols • For some elements, the chemical symbol is derived from the original Latin name.
Types of Elements • Elements can be divided into three classes: • Metals • Nonmetals • Semimetals or metalloids • Semimetals have properties midway between those of metals and nonmetals.
Metal Properties • Metals are typically solids with high melting points and high densities and have a bright, metallic luster. • Metals are good conductors of heat and electricity. • Metals can be hammered into thin sheets and are said to be malleable. • Metals can be drawn into fine wires and are said to be ductile.
Nonmetal Properties • Nonmetals typically have low melting points and low densities and have a dull appearance. • Nonmetals are poor conductors of heat and electricity. • Nonmetals are not malleable or ductile and crush into a powder when hammered. • Eleven nonmetals occur naturally in the gaseous state.
Periodic Table of the Elements • Each element is assigned a number to identify it. It is called the atomic number. • Hydrogen’s atomic number is 1; helium is 2; up to uranium, which is 92. • The elements are arranged by atomic number on the periodic table.
Metals, Nonmetals, & Semimetals • Metals are on the left side of the periodic table, nonmetals are on the right side, and the semimetals are in between.
Physical States of the Elements Shown are the physical states of the elements at 25 °C on the periodic table.
Law of Definite Composition • The law of definite composition states that “Compounds always contain the same elements in a constant proportion by mass.” • Water is always 11.19% hydrogen and 88.81% oxygen by mass, no matter what its source. • Ethanol is always 13.13% hydrogen, 52.14% carbon, and 34.73% oxygen by mass.
Chemical Formulas • A particle composed of two or more nonmetal atoms is a molecule. • A chemical formula is an expression of the number of and types of atoms in a molecule. • The chemical formula of sulfuric acid is H2SO4.
Writing Chemical Formulas • The number of each type of atom in a molecule is indicated with a subscript in a chemical formula. • If there is only one atom of a certain type, no “1” is used. • A molecule of the vitamin niacin has six carbon atoms, six hydrogen atoms, two nitrogen atoms, and one oxygen atom. What is the chemical formula? C6H6N2O
Interpreting Chemical Formulas • Some chemical formulas use parentheses to clarify atomic composition. • Ethylene glycol, a component of some antifreezes, has a chemical formula of C2H4(OH)2. It contains two carbon atoms, four hydrogen atoms, and two OH units, giving a total of six hydrogen atoms and two oxygen atoms. How many total atoms are in ethylene glycol? • Ethylene glycol has a total of ten atoms.
Physical and Chemical Properties • A physical property is a characteristic of a pure substance that we can observe without changing its composition. • Physical properties include appearance, melting and boiling points, density, conductivity, and physical state. • A chemical property describes the chemical reactions of a pure substance.
Chemical Properties Sodium metal (Na) reacts with chlorine gas (Cl2) to produce sodium chloride (NaCl).
Physical and Chemical Change • A physical change is a change where the chemical composition of the substance is not changed. • These include changes in physical state or shape of a pure substance. • A chemical change is a chemical reaction. • The composition of the substances changes during a chemical change.
Evidence for Chemical Changes • Gas release (bubbles) • Light or release of heat energy • Formation of a precipitate • A permanent color change
Conservation of Mass • Antoine Lavoisier found that the mass of substances before a chemical change was always equal to the mass of substances after a chemical change. • This is the law of conservation of mass. • Matter is neither created nor destroyed in physical or chemical processes.
Conservation of Mass Example • If 1.0 gram of hydrogen combines with 8.0 grams of oxygen, 9.0 grams of water is produced. • Consequently, 3.0 grams of hydrogen combine with 24.0 grams of oxygen to produce 27.0 grams of water. • If 50.0 grams of water decompose to produce 45.0 grams of oxygen, how many grams of hydrogen are produced? 50.0 g water – 45.0 g oxygen = 5.0 g hydrogen
Potential and Kinetic Energy • Potential energy, PE, is stored energy; it results from position or composition. • Kinetic energy, KE, is the energy matter has as a result of motion. • Energy can be converted between the two types. • A boulder at the top of the hill has potential energy; if you push it down the hill, the potential energy is converted to kinetic energy.
KE, Temperature, and Physical State • All substances have kinetic energy regardless of their physical state. • Solids have the lowest kinetic energy, and gases have the greatest kinetic energy. • As you increase the temperature of a substance, its kinetic energy increases.
Law of Conservation of Energy • Just like matter, energy cannot be created or destroyed, but it can be converted from one form to another. • This is the law of conservation of energy. • There are six forms of energy: • Heat • Light • Electrical • Mechanical • Chemical • Nuclear
Energy and Chemical Changes • In a chemical change, energy is transformed from one form to another. For example:
Law of Conservation of Mass and Energy • Mass and energy are related by Einstein’s theory of relativity, E = mc2. • Mass and energy can be interchanged. • The law of conservation of mass and energy states that the total mass and energy of the universe is constant.