1 CH 4: Matter and Energy Renee Y. Becker CHM 1025 Valencia Community College

2 Physical State of Matter Matter is any substance that has mass and occupies volume. Matter exists in one of three physical states: –solid –liquid –gas

3 Gases 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.

4 Liquid 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.

5 Solid 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.

6 Phases

7 Changes in Physical State Most substances can exist as either a solid, liquid, or 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.

8 Solid  Liquid 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.

9 Liquid  Gas 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.

10 Solid  Gas 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.

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12 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.

13 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.

14 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.

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16 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 the Earth’s crust:

17 Elements Oxygen is the most common element in both the Earth’s crust and in the human body. While silicon is the second most abundant element in the crust, carbon is the second most abundant in the body.

18 Elements Each element has a unique name. Each element is abbreviated using a chemical symbol. The symbols are 1 or 2 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.

19 Elements Elements can be divided into three classes: –metals –nonmetals –semimetals or metalloids Semimetals have properties midway between those of metals and nonmetals.

20 Metals 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.

21 Non-metals 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. 11 nonmetals occur naturally in the gaseous state.

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23 Periodic Table Each element is assigned a number to identify it. It is called the atomic number. Hydrogen is 1; helium is 2; up to uranium, which is 92. The elements are arranged by atomic number on the periodic table.

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25 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.

26 Chemical Formula A particle composed of two or more nonmetal atoms is a molecule. A chemical formula expresses the number and types of atoms in a molecule. The chemical formula of sulfuric acid is H 2 SO 4.

27 Chemical Formula 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. Some chemical formulas use parentheses to clarify atomic composition.

28 Example 1: Molecular Formula Glucose contains 6 carbons, 12 hydrogens, and 6 oxygens. Write the molecular formula for glucose

29 Example 2: Molecular Formula List how many of each type of element the following compounds have A)H 2 O B)NH 3 C)C 2 H 4 (OH) 2

30 Physical & 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.

31 Physical & 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.

32 Evidence for Chemical Changes gas release (bubbles) light or release of heat energy formation of a precipitate a permanent color change

33 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.

34 Example 3: Conservation of Mass C (s) + O 2(g)  CO 2(g) a)12.3g C reacts with 32.8g O 2, ?g CO 2 b)0.238g C reacts with ?g O 2 to make.873g CO 2 c)?g C reacts with 1.63g O 2 to make 2.24g CO 2

35 Potential & 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.

36 Energy

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38 KE, Temperature, and Physical State All substances have kinetic energy no matter what physical state they are in. 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.

39 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, and nuclear.

40 Energy and Chemical Changes In a chemical change, energy is transformed from one form to another.

41 Law of Conservation of Mass & Energy Mass and energy are related by Einstein’s theory of relativity, E = mc 2. 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.