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UT Arlington CHEM 1465 - LeChatelier's principle

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Chem 1465 1st Edition Lecture 16Outline of Last Lecture 1. Intro to chemical equilibrium2. Equilibrium constants3. Gas phase equilibria: Kp and Kc4. Homogenous and heterogeneous equilibria 5. Variations in the form of the reaction and K6. ICE tableOutline of Current Lecture 1. LeChatelier’s PrincipleA. Change in concentrationB. Change in pressure C. Change in temperature 2. Acids and bases 3. Auto ionization of water Current Lecture1. LeChatelier’s Principle: we can influence the position of an equation; if a stress is appliedto a reaction mixture at equilibrium the net reaction will shift to regain equilibriumA. Change in concentration- Q=K when the reaction is at equilibrium- Q<K the reaction must shift to the right (reactants consumed and produces formed)These 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.- Q>K the reaction must shift to the left (consuming products and forming reactants)- Adding reactants will make the equation favor products- Removing something will make the reaction move in the direction of the removed elementB. Change in pressure- Three ways to change pressure:a. Add or removed gaseous reactants; reduce pressure in reactants, direction will move to reactantsb. Change volume of container; reduce the volume, reduce the gas molecules; increase volume, increase gas moleculesc. Add an inert gas (not involved in the reaction); Q=K so you remain at equilibrium C. Change in temperature- Temperature affects K, we need to include enthalpy to determine the effect.- Exothermic reactions: increase in temperature- shifts left. Decreases in temperature- shifts right- Endothermic reactions: increase in temperature- shifts right. Decrease in temperature- shifts left - Effects of a catalyst: doesn’t affect K, but speeds up the rate at which the reaction reaches equilibrium. 2. Acids and bases- Bronsted Lowry acid: proton donor- Bronsted Lowry base: proton acceptor- Amphoteric: molecules can be both a proton donor and acceptor (water)- Conjugate acid: product that has 1 more proton and or 1 fewer negative charge- Conjugate base: product that has 1 fewer proton and addition of negative charge- Generic equation: HA →H+ + A- where HA is acid, H+ is conjugate acid, and A- is the conjugate base. Ka = H +¿¿A−¿¿¿¿ - If Ka is large, the stronger the acid. There a 7 strong acids: HBr, HCl, HI, HNO3 , H2SO4, HClO3 , HClO4- To be a strong acid means the proton will completely dissociate leaving 100% of A-3. Auto ionization of water- Water is amphoteric meaning it can be acid or base- Kwater = [H+][-OH]- At 25 degrees Celsius, Kw is 1E-14- So in pure water, [H+] = [-OH] = 1E-7- The pH scale is a nice way to represent [H] without scientific notation- pH= -log[H+] or [H+] =


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UT Arlington CHEM 1465 - LeChatelier's principle

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