chapter 15 general equilibrium.pptx - California Distinguished School Piedmont Hills High School 1377 Piedmont Road \u2022 San Jos\u00e9 California 95132-2497

chapter 15 general equilibrium.pptx - California...

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California Distinguished SchoolP i e d m o n t H i l l s H i g h S c h o o l1377 Piedmont Road • San José, California 95132-2497Telephone: (408) 347-3800 • Fax: (408) 347-3805Chemical EquilibriumMR. L. MACASAETROOM D13
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Reversible ReactionsA chemical reaction in which the products can regenerate the original reactants. Theoretically, all chemical reactions are reversible; some on their own and others under restricted conditions.
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Reversible ReactionsTwo half arrows are used to denote a reversible reaction, which simply means that the reaction can proceed in either way.Example: 2NO2(g) ⇌ N2O4(g) Here, the formation of N2O4is called the forward reaction. The formation of NO2is called the reverse reaction.
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The concept of equilibriumAs a system approaches equilibrium, both the forward and reverse reactions are occurring.At equilibrium, the forward and reverse reactions are proceeding at the same rate.N2O4(g) ⇌ 2NO2(g)
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The concept of equilibriumOnce equilibrium is achieved, the amount of each reactant and product remains constant.N2O4(g) ⇌ 2NO2(g)
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A system at equilibriumRates become equalConcentrations become constantN2O4(g) ⇌ 2NO2(g)
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Chemical equilibriumThis is the state in which the concentrations of reactants and products remain constant with time. This is because the rate at which they are formed in each reaction equals the rate at which they are consumed in the opposite reaction.On the molecular level, there is frantic activity. Equilibrium is not static, but is a highly dynamic situation. It is said to be macroscopically static but microscopically dynamic.
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Chemical equilibriumConsider a reaction described below:aA + bB ⇌ cC + dD; where a, b, c and d are the coefficients of the substances A, B, C and D. The equilibrium constant, Keqis defined as follows:Keq= This is known as the “equilibrium expression” or the “Law of Mass Action”
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The equilibrium constant, KK always has the same value at a given temperature regardless of the amounts of reactants or products that are present initially.For a reaction at a given temperature, there are infinite equilibrium positions but only one value for K. (Equilibrium position is a set of equilibrium concentrations)K values are customarily written without units.
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The equilibrium constant, KExample 1: What is the equilibrium constant for the following reaction: 2NO2(g) ⇌ N2O4(g) Keq= Example 3: What is the equilibrium constant for the following reaction:2CO (g) + O2(g) ⇌ 2CO2(g)Keq=
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The equilibrium constant, KConsider a reaction described below:aA(g) + bB(g) ⇌ cC(g) + dD(g)The equilibrium constant can also be written in terms of the equilibrium partial pressures (KP) of the gases:KP=
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The equilibrium constant, KExample: The reaction for the formation of nitrosyl chloride 2NO(g) + Cl2(g)  2NOCl(g)was studied at 25OC. The pressures at equilibrium were found to be as follows:PNOCl= 1.2 atmPNO= 5.0x10-2atmP = 3.0x10-1atmCalculate KPfor this reaction at 25OC.
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