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# UW-Milwaukee CHEM 100 - Physical Change

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CHEM 100 1st Edition Lecture 3Physical Change-Changing of Physical Properties without changing chemical composition-Ex: A change of state (solid to gas), an expected change in color, a magnet divides magneticmaterials from nonmagnetic materials without changing their identitiesChemical Change-Ability of a substance to undergo chemical reactions-Ex: Tarnishing, burning, reactions of elements forming something, bubbling, permanent colorchange, sudden change in temperatureChemical Properties-Ability of a substance to undergo chemical reactions-Ex: Iron rusts, gold is unreactiveEnergy-Capacity to do work (when a force acts over a distance) or to transfer heat-There are two kinds of energy-Kinetic: Energy of motion (Ex: A ball rolling downhill possesses kinetic energy)-Potential: Energy possessed by an object (Ex. A ball at rest has potential energy)-All other energies (chemical, mechanical, electrical, heat, etc.) are forms of these two-When chemical or physical changes occur, energy changes do as well-Some processes require energy, while some release energy, some can do bothThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Scientific Notation-A number expressed as “C * 10^n” where “c” is the coefficient (must be greater than 1 and less than10), and n is the exponent (positive or negative integer)-Moving the decimal point to the left increases the exponent, moving it to the right decreasesthe exponent-When multiplying numbers in scientific notation, multiply the coefficients and add the exponents.- Ex. (4.0 * 10^6) (1.5 * 10^-3) = (4.0 * 1.5) * 10^6+ (-3) = 6.0 * 10^3-When dividing numbers, divide coefficients and subtract exponents-Ex. (4.0 * 10^-2) / (2.0 * 10^3) = (4.0 * 1.5) * 10^(-2)-3 = 2.0 * 10^-5-When passing numbers to a power, raise the coefficient to that power, then multiply exponentsPrecision and Accuracy-The precision of a number is the extent of the agreement between repeated measurements of its valueDimensional Analysis-Possible Approach to the problem solving in four steps1. What are we given / what are we looking for?2. What relationships can we use?3. Set up problem4. Check your answerEx. How many inches are in 2 kilometers? 1. This problem is asking for a conversion to inches2. 1 km = 1000 m, 1m = 100 cm, 1in = 2.54cm3. 2km * 111m/1km * 100cm/1m * 1in/2.54cm = 8*10^4 in4. DOUBLE CHECK ANSWERScientific Inquiry-Scientific Method: an approach to asking questions and seeking answers that employs a variety of tools,techniques, and strategies.-Hypotheses: a tentative explanation for the properties or behavior of matter that accounts for a set of observations and can be tested. Because hypotheses are usually starting points in the explanation of natural phenomena, they normally lead to further experimentation.-Laws: A statement with universal validity. -Law of conservation of mass: the mass of products obtained from a chemical reaction equals the mass of the substances that react – mass is not lost or gained in a chemical reaction. Every known chemical reaction that has been studied follows this law. When accommodated with new information, this law transformed into the law of conservation of mass and energy.-The Law of Definite Proportions: A compound always has the same relative amounts of elements that compose it.-Theories: explain why observations, hypotheses, or laws apply under many different.- Dalton's atomic theory: 1. All matter is composed of exceedingly small, indivisible particles, called atoms. 2. All atoms of a given element are identical both in mass and in chemical properties. However, atoms of different elements have different masses and different chemical properties. 3. Atoms are not created or destroyed in chemical reactions. 4. Atoms combine in simple, fixed, whole-number ratios to form compounds.-Lots of evidence was needed to show matter is composed of atoms, for even with a powerfulmicroscope, we cannot see them. The scanning tunneling microscope allows us to see images at an atomic level. -None of his original ideas for the theory were completely, accurate, but they were close.-In a chemical reaction, atoms rearrange into new combinationsStructure of an Atom-Atoms are divisible, they are composed of subatomic particles:-One kind is found in the nucleus-Electron: Negatively charged subatomic particle-Two kinds are found outside of the nucleus-Proton: Positively charged particle-Neutron: Uncharged particleNuclear Atom- Thomson's model of atomic structure, called the “plum pudding” model, assumed that protons and electrons were evenly distributed throughout the atom.- In 1907 Rutherford conducted an experiment, predicting the need of a nucleus in an atom, suggesting that the nucleus contains the protons and most of the mass of the atom. The electrons exist outside the nucleus in what is often called an “electron cloud.” This is when he hypothesized the

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