CH 4: Matter and Energy

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.

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.

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.

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.

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 H2SO4.

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 • H2O • NH3 • C2H4(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) + O2(g) CO2(g) • 12.3g C reacts with 32.8g O2, ?g CO2 • 0.238g C reacts with ?g O2 to make .873g CO2 • ?g C reacts with 1.63g O2 to make 2.24g CO2

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

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 = 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.