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Unit 1 Introduction Matter and Change What is Chemistry? Chemistry is the study of matter and its interactions. We will study the following properties of matter: • composition • properties • interactions • changes How will matter be studied? Using the scientific method. What is the Scientific Method? Logical approach to exploring a problem or question that has been raised through observation. Designed to produce a solution or answer that can be tested, retested, and supported by experimentation. What are the steps of the Scientific Method? 1.State the problem. 2.Gather information about the problem. 3.Form a hypothesis. 4.Test hypothesis. - variables - controlled experiments 5.Gather and organize data and observations. 6.Interpret data. 7.Form a conclusion. 8.Replication. What happens to a hypothesis? Model: An explanation of how phenomena occur and how data or events are related. Theory: A broad generalization that explains a body of facts or phenomena. Scientific Law: Statement or mathematical expression about behavior of the natural world. Use the following terms to organize a Concept Map for matter. •Can it be separated? •Is composition uniform? •Can it be decomposed by ordinary chemical means? •Elements •Compounds •Mixtures •Pure Substance •Heterogeneous mixture •Homogeneous mixture •Air •Stainless steel •Blood •Wood •Water •Sodium chloride •Gold •Oxygen Matter Matter – anything that has mass and volume. How is matter classified? Matter is broken down into two major categories - Pure Substance - Mixture Pure Substance - Have unique properties - Cannot be separated by physical means - There are two categories of pure substances: Elements and Compounds Elements - simplest pure substances - contain only one kind of atom - cannot be broken down by physical or chemical means - unique physical and chemical properties Compounds - substance composed of 2 or more elements that are chemically combined - have unique chemical and physical properties - can be broken down chemically (not physically) - properties of elements that compounds are broken down into do not resemble properties of original compound - always break down to the same proportion by mass Mixtures - Collection of 2 or more pure substances physically mixed together. (No chemical formula) - Properties vary depending on what is in the mixture - Composition can vary (no definite proportion) - There are 2 types of mixtures: Heterogeneous Homogeneous Homogeneous Mixture - Substances are distributed evenly throughout the mixture - All regions are identical in their composition and properties Heterogeneous Mixture - Substances are not evenly distributed throughout the mixture - Some regions have different properties than others Classification of Matter Matter is described by its properties Extensive Properties - Depend on how much of a substance there is - Not useful in identifying the substance. Intensive Properties - Properties that do not depend on size. - Can be useful in identifying the substance. Comparing Extensive and Intensive Properties Physical Properties - Characteristics that can be observed without changing the substance. - Melting point and boiling point are examples Physical Change - Change in a substance that does not involve a change in the identity of the substance. - Phase changes are examples: solid to liquid liquid to solid liquid to gas gas to liquid solid to gas gas to solid - melting freezing vaporization condensation sublimation deposition Phase Changes are also called changes in state. Plasma There are 4 states of matter: Solid Liquid Gas Phase Diagrams A phase diagram is a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist. The triple point of a substance indicates the temperature and pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium. The critical point of a substance indicates the critical temperature and critical pressure. Phase Diagram Phase Diagram Phase Diagram for CO2 Changes of State - Summary Water in Three States Heating Curve for Water Heat of Fusion: The amount of energy as heat required to melt a solid at the solid’s melting point Heat of Vaporization: The amount of energy as heat that is needed to vaporize a liquid at the liquid’s boiling point at constant pressure Chemical Properties - characteristics that describe how a substance interacts (or fails to interact) with other substances. Chemical Change - also called a chemical reaction - change that results in production of 1 or more substances that differ in chemical properties and composition from the original substance Chemical Reaction Evidence of a Chemical Change Comparison of Physical and Chemical Properties Comparing Physical and Chemical Properties Comparing Chemical and Physical Changes Periodic Table of the Elements Review Questions 1. 2. 3. 4. 5. Matter that has a definite shape and a definite volume is? Why is air considered a mixture and not a compound? How do compounds differ from mixtures? Is each of the following a chemical or physical property? A. Its mass is 124.3 g. B. It is a shiny solid at room temperature. C. It is easily etched by nitric acid. D. It melts when heated to 670°C. E. It is 31.7 centimeters long. F. It is a good heat conductor. G. It burns in air. H. It is a good conductor of electrical energy Describe the difference between a chemical change and a physical change. Give one example of each kind of change.