CHEM 1030 Week 13 Notes
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This 6 page Class Notes was uploaded by Alyssa Anderson on Saturday April 9, 2016. The Class Notes belongs to CHEM 1030 at a university taught by Dr. Streit in Spring 2016. Since its upload, it has received 14 views.
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Date Created: 04/09/16
Chemistry Notes Week 13 NOTE: May 1st- Chemistry ﬁnal review session An oxidation-reduction (or redox) reaction is a chemical reaction in which electrons are transferred from one reactant to another A. Oxidation is the loss of electrons B. Reduction is the gain of electrons 2+ C. Reducing agents (Zn loses two electrons and is oxidized to Zn ) 2+ D. Oxidizing agent (Cu gains two electrons and is reduced to Cu) E. A redox reaction is the sum of an oxidation half-reaction and a reception half- reaction The oxidation number is the charge an atom if electron were transferred completely A. H2(g) + F2(g) —> 2HF(g) B. The oxidation number of H i2 0 C. The oxidation number of F i2 0 D. The oxidation number of HF (+1)(-1) Oxidation Numbers (Assign the numbers to the elements in the compound KMnO4-) A. Step 1: Start with the oxidation numbers you know 1. K is +1 2. O4 is -8 (-2x4) 3. So Mn has to be -7 B. Step 2: The numbers in the boxes (total contribution to charge) must sum to the original charge To assign oxidation numbers: A. The oxidation number of an element, in it elemental form, is 0 B. Figure out the charges through the periodic table C. Know the elements that nearly always have the same oxidation number Oxidation of Metals in Aqueous Solutions A. In a displacement reaction, an atom or an ion in a compound is replaced by an atom of another element B. Zinc displaces (replaces) copper in the dissolved salt C. Zn is oxidized to Zn 2+ D. Cu 2+ is reduced to Cu Concentration of Solutions A. Molarity (M), or molar concentration, is deﬁned as the number of moles of solute per liter of solution B. Molarity (M) = moles solute (moles) / liters solution (L) C. Can also be written as L = mol/M D. Can also be written as mol = M x L Dilution A. Dilution is the process of preparing a less concentrated solution from a more concentrated one B. Moles of solute before dilution = moles of solute after dilution C. Example: In an experiment, a student needs 1.00 L of a 4.00 M KMnO4 solution. A stock solution of 1.00 M KMnO4 is available. How much of the stock is needed? 1. Use the relationship that moles of suction before dilution = moles of solution after dilution to ﬁnd the missing part. 2. To make the solution: pipet 400 mL out of solution and into 1.00 L volumetric ﬂask and carefully dilute to the calibration mark D. Because most volumes measured in the laboratory are in milliliters rather than liters, it is worth pointing out that the equation can be written as M x cL = M c mL d d E. A series of dilutions that may be used to prepare a number of increasingly dilute solutions is called serial dilution 1. Step 1: Prepare a dilute solution from the stock 2. Step 2: Dilute portion of the prepared solition to make a more dilute solution 3. Step 3: Repeat as needed Chapter 10 Energy and Energy Changes A. The systems is a part of the universe that is of speciﬁc interest B. The surroundings constitute the rest of the universe outside the system C. Universe = System + Surroundings D. The system is usually deﬁned as the substances involved in chemical and physical changes E. Thermochemistry is the study of heat (the transfer of thermal energy ) F. Heat is the transfer of thermal energy G. Heat is either absorbed or released during a process H. SI Unit is a Joule (J). Often calories are used and 1 calorie is the amount of heat required to raise 1 g of water by 1*C I. 1 cal = 4.184 J J. calorie is not the same as a nutritional calories (Cal) K. 1 Cal = 1000 cal L. An exothermic process occurs when heat is transferred from the system to the surroundings (“Feels hot!”) M. An endothermic process occurs when heat is transferred from the surroundings to the system (“Feels cold!”) Thermodynamics A. Thermodynamics is the study od the interconversion of heat and other kinds of energy B. In thermodynamics, there are three types of systems: 1. An open system can exchange mass and energy with the surroundings 2. A closed system allows the transfer of energy but not mass 3. An isolated system does not exchange either mass or energy with its surrounding States and State Functions A. State function are properties that are determined by the state of the system, regardless of how the condition was achieved B. The magnitude of chmage depends only on the initial and ﬁnal states of the system 1. Energy 2. Pressure 3. Volume 4. Temperature The First Law of Thermodynamics A. *triangle* U is the change in the internal energy B. “sys” and “surr” denote system and surroundings, respectively C. *triangle* U = Uf- Uiis the different of the erengies of the initial and ﬁnal states Work and Heat A. The overall change in the systems initial energy is given by *triangle* U = q + w B. q is heat 1. q is positive for an endothermic process (heat absorbed by the system) 2. q is negative for an exothermic process (heat released by the system) C. w is work 1. w is positive for work done ON the system 2. w is negative for work done BY the system ΔU = q + w Enthalpy: Reactions Carried Out at Constant Volume or at Constant Pressure A. Sodium azide detonates to give a large quantity of nitrogen gas B. 2NaN3(s) —> 2Na(s) + 3N2(g) C. Under constant volume conditions, pressure increases D. Under constant pressure, volume increases E. Pressure-volume or PV work, is done when there is a volume change under constant pressure (w = -P*triangle*V) F. P is the external opposing pressure G. *triangle* V is the change in the volume of the container H. Under conditions of constant pressure, ΔU = q − PΔV AND ΔU = q + w Enthalpy A. The thermodynamic function of a system called enthalpy (H) is defined by the equation H = U + PV B. Pressure: pascal; 1Pa = 1 kg/(m s ) . 2 C. Volume: cubic meters; m 3 D.PV: 1kg/(m s ) x m = 1(kg m )/s = 1 J 2 E. Enthalpy: joules Equations A. For any process, the change in enthalpy is ΔH = ΔU + Δ(PV) B. If pressure is constant, ΔH = ΔU + PΔV C. Rearrange to solve for ΔU = ΔH + PΔV D. Remember, q = Δp + ΔV E. Substitute equation 3 into equation 4 and solve: q = (Δp − PΔV) + PΔV F.q p ΔH for a constant-pressure process G. The enthalpy of reaction (ΔH) is the difference between enthalpies of the products and the enthalpies of the reactants H. ΔH = H(products) – H(reactants) I. Assumes reactions in the lab occur at constant pressure 1. ΔH > 0 (positive)—> endothermic process 2. ΔH < 0 (negative) —> exothermic process
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