GeneralChemistry_7.ppt - GENERAL CHEMISTRY Chapter 6 Chemical Equilibrium Dr Huynh Ky Ph\u01b0\u01a1ng Ha Office 112 B2 Building Phone 38650484 Email

GeneralChemistry_7.ppt - GENERAL CHEMISTRY Chapter 6...

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GENERAL CHEMISTRY GENERAL CHEMISTRY Chapter 6 Chapter 6 Chemical Equilibrium Chemical Equilibrium Dr. Huynh Ky Ph ng H ươ a Office: 112 B2 Building Phone: 38650484 Email: [email protected]
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Consider colorless frozen N 2 O 4 . At room temperature, it decomposes to brown NO 2 : N 2 O 4 ( g ) 2NO 2 ( g ). After some time, the color stops changing and we have a mixture of N 2 O 4 and NO 2 . Chemical equilibrium is the point at which the concentrations of all species are constant. Chemical equilibrium occurs when the reaction in the reverse direction proceed at equal rates. The Concept of Equilibrium The Concept of Equilibrium
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Using the collision model: At the beginning of the reaction, there is no NO 2 so the reverse reaction (2NO 2 ( g ) N 2 O 4 ( g )) does not occur. • Only the production of NO 2 will occur. As the amount of NO 2 builds up, there is a chance that two NO 2 molecules will collide to form N 2 O 4 . Thus, the forward chemical reaction has an opposing reaction that will increase with the increase in product formation. Collision Model: Understanding Collision Model: Understanding Equilibrium Equilibrium
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The point at which the rate of decomposition: N 2 O 4 ( g ) 2NO 2 ( g ) equals the rate of dimerization: 2NO 2 ( g ) N 2 O 4 ( g ). is dynamic equilibrium. The equilibrium is dynamic because the reaction has not stopped: the opposing rates are equal. Dynamic Equilibrium Dynamic Equilibrium
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At equilibrium, as much N 2 O 4 reacts to form NO 2 as NO 2 reacts to re-form N 2 O 4 : The double arrow implies the process is dynamic. Consider Forward reaction: A B Rate = k f [A] Reverse reaction: B A Rate = k r [B] At equilibrium k f [A] = k r [B], which implies The mixture at equilibrium is called an equilibrium mixture. Expressing Equilibrium Reactions Expressing Equilibrium Reactions N 2 O 4 ( g ) 2NO 2 ( g ) A B
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The Equilibrium Constant The Equilibrium Constant No matter the starting composition of reactants and products, the same ratio of concentrations is achieved at equilibrium.
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Defining the Equilibrium Constant Defining the Equilibrium Constant For a general reaction in the gas phase the equilibrium constant expression is where K eq is the equilibrium constant. a A + b B c C + d D b a d c eq P P P P K B A D C
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The Equilibrium Constant The Equilibrium Constant For a general reaction the equilibrium constant expression for everything in solution is where K eq is the equilibrium constant, A, B, C, and D are the reactants and products, and a, b, c, and d are the stoichiometric coefficients. a A + b B c C + d D b a d c eq K B A D C
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Meaning of Equilibrium Meaning of Equilibrium Constant Constant K>>1: reaction is product-favored; equilibrium concentrations of products are greater than equilibrium concentrations of reactants.
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