Matter and Change Chemistry Chapter 1
Try to Answer the Following Questions 1. A compound is formed by… • A single element • Two or more atoms • Two or more nuclei • Electrons and neutrons • Which statement best describes atoms and molecules in a liquid? • They vibrate rapidly • They form a definite structure • They slide past each other • They cannot be rearranged • What is the process of a liquid changing to a gas called? • Ice melting into water is a physical or chemical change? • Which state of matter has neither a definite shape nor definite volume?
How did you do? • “B”: two or more atoms • “C”: atoms and molecules in a liquid slide past each other • Evaporation • Physical • Gas
Introduction • What is chemistry? • The study of the composition of substances and the changes (both physical and chemical) they undergo • What lead to the development of chemistry? • Alchemy • What other sciences does chemistry contribute to? • Biology • Geology • Physics
What does a Chemist do? • Develop new products (meds., cosmetics) • Find methods to reduce pollution/clean up environment • Teaching • Analyzing substances • Quality of manufactured products • Applied Chemistry: using knowledge to attain specific goals (a.k.a. chemical technology) • Knowledge can be used to help or hurt people/environment
Branches • Organic Chemistry • The study of all substances that come from carbon • Inorganic Chemistry • The study of all substances without carbon • Analytical Chemistry • The study of the composition of substances • Physical Chemistry • Theories and experiments that describe the behavior of chemistry • Biochemistry • The study of chemistry of living organisms
Hypothesis vs. Theory vs. Scientific Law • A HYPOTHESIS is a proposed reason for what is observed and it needs to be tested by means of an experiment • A THEORY is a thoroughly tested explanation of why experiments give certain results. • A theory tends to explain WHY things happen. You cannot prove a theory. • Scientific Law is a concise statement that summarizes the results of a broad spectrum of observations and experiments. • Scientific Law tends to explain WHAT things happen. You can prove a scientific law.
Why does it “matter”? • What is matter? • “Everything that takes up space and has mass” • “Stuff” • What is mass? Amount of matter an object contains “How much stuff an object has” **This is NOT the same as weight
Substances vs Mixtures • Matter is broken into categories. Matter can be either a substance or a mixture. • A substance is a particular kind of matter that has a uniform composition. This means that no matter the sample it will always have the same physical properties. • Eg. Elements and compounds • Other examples are: salt (NaCl), Fe, Ag, Pb, water • What about lemonade?
Mixtures • A mixture is a physical blend of two or more substances. It has a variable composition and can be made of different ratios of substances. • Mixtures are ALWAYS physical changes
Types of mixtures • Heterogeneous mixtures -not uniform in composition -more than one phase (a phase is a part of a system that is uniform in composition and physical state) -examples: tossed salad, gravel mix, rock, river water
Homogeneous mixtures -uniform in composition -also called a solution -easily confused with substances -examples: salt water
A good question to ask yourself when trying to decide if something is a substance or a homogeneous mixture is to ask yourself if there is more than one kind of this material. • What is gasoline? • What is milk? • Are there different concentrations of salt?
Separating a Mixture • There are several ways to separate a mixture. A good way to figure out if matter is a substance or a solution is to see if you can separate it into parts by doing one of the following: • Physical separation • Filter (particle size, uses gravity) • Magnet (magnetism) • Decanting-pouring off a liquid (density) • Distillation (boiling point) • Centrifuging (density) • Chromatography (separates based on solubility) • Crystallization
Lab: Classifying Matter At each station, record answers to the following: 1) Identify the category of matter:a. Is it a pure substance? If so then is it an element or is it a compound? b. Is it a mixture? If so, then is it a heterogeneous mixture or homogeneous mixture? c. Write down the criteria you use for your categorization schemes. 2) Devise a separation strategy for any mixtures found. In other words, if you think you’ve spotted a mixture, how would you separate it into different components, and (if possible) all the way to the pure substances that comprise the mixture? (Remember, pure substances cannot be separated by physical means. They must be separated chemically, or, in the case of elements, by splitting atoms! That’s beyond the scope of the activity for the day.)
Physical Properties • Matter contains both physical and chemical properties. • A physical property is a quality or condition of a substance that can be measured or observed without changing the substance’s composition. • Examples: Color, mass, density, hardness, odor, boiling point, solubility
Chemical Properties • Chemical properties are a little more difficult to determine. A chemical property is the ability of a substance to undergo chemical reactions • IE: Rot, rust, decompose, decay, grow ferment You know that a chemical change has taken place because of a substance’s chemical properties.
Chemical vs. Physical Changes • Chemical Change • A change in the composition of a substance OR • Changing a substance to form a new substance • Examples: fermenting, rotting, burning, color change, gas given off • Physical Change • A change in a substance without a change in its composition • Examples: mixing, cutting, changing from a solid to a liquid
Physical Property • Something that can be observed without altering the chemical state • Example: color, boiling point
Physical Change • A change that occurs without forming a new substance • Example: melting • DOES NOT FORM OR BREAK BONDS!
Chemical Property • Property of a substance related to a chemical change undergone by the substance • Example: metal dulls in air
Chemical Change • A reaction occurs and one or more new substances are formed • Example: Rusty cars
Figure it out- Chemical or Physical? • Metals are shiny • Argon is put in light bulbs because it doesn’t react • Milk gets sour when left out • Metals can be made into wires • Bread rises when cooked • Nonmetals are not able to conduct electricity
What is the basic difference between a chemical and a physical change? • After a physical change, it is still the same substance (composition). -After a chemical change, you have a NEW substance
States of Matter • There are four states of matter: solid, liquid, gas • Solid -definite shape, definite volume • Liquid -indefinite shape, definite volume • Gas -indefinite shape, indefinite volume • Plasma –gas like What is compressibility? Ability to squash something into a smaller volume
Solid, Liquid, Gas (a) Particles in solid (b) Particles in liquid (c) Particles in gas
Gas, Liquid, and Solid Gas Liquid Solid Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 441
Some Properties of Solids, Liquids, and Gases Property Solid Liquid Gas Shape Has definite shape Takes the shape of Takes the shape the container of its container Volume Has a definite volume Has a definite volume Fills the volume of the container Arrangement of Fixed, very close Random, close Random, far apart Particles Interactions between Very strong Strong Essentially none particles
Solid H2O(s) Ice Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31
Ice Photograph of snowflakes Photograph of ice model H2O(s) Ice Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31
Liquid In a liquid • molecules are in • constant motion • there are appreciable • intermolecular forces • molecules are close • together • Liquids are almost • incompressible • Liquids do not fill the • container H2O(l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31
Liquids The two key properties we need to describe are EVAPORATION and its opposite CONDENSATION add energy and break intermolecular bonds EVAPORATION CONDENSATION release energy and form intermolecular bonds
Gas H2O(g) Steam Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31
Evaporation • To evaporate, molecules must have sufficient energy to break IM forces. • Molecules at the surface break away and become gas. • Only those with enough KE escape. • Breaking IM forces requires energy. The process of evaporation is endothermic. • Evaporation is a cooling process. • It requires heat.
Condensation Change from gas to liquid Achieves a dynamic equilibrium with vaporization in a closed system. What is a closed system? A closed system means matter can’t go in or out. (put a cork in it) What the heck is a “dynamic equilibrium?”
Dynamic Equilibrium When first sealed, the molecules gradually escape the surface of the liquid. As the molecules build up above the liquid - some condense back to a liquid. The rate at which the molecules evaporate and condense are equal.
Dynamic Equilibrium As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense. Equilibrium is reached when: Rate of Vaporization = Rate of Condensation Molecules are constantly changing phase “dynamic” `The total amount of liquid and vapor remains constant “equilibrium”
Vaporization • Vaporization is an endothermic process - it requires heat. • Energy is required to overcome intermolecular forces • Responsible for cool earth • Why we sweat
Energy Changes Accompanying Phase Changes Gas Vaporization Condensation Sublimation Deposition Energy of system Liquid Melting Freezing Solid Brown, LeMay, Bursten, Chemistry2000, page 405