CHEM 14B Lecture Notes - Lecture 1: Molar Concentration, Equilibrium Constant, Ammonia

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turquoisemoose666

4 Jan 2021

School

UCLA

Department

Chemistry and Biochemistry

Course

CHEM 14B

Professor

Lavelle, L.

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Document Summary

At molecular level: r forming p & reverse reaction p forming r (but at an equal rate) Under same conditions, reaction at equilibrium has same p/r ratio. Equilibrium constant (kc): ratio of the concentration of the product to the concentration of the reactant. Tells the relative stability of the products and reactants. Reaction at equilibrium aa + bb cc + dd. A, b, c, d: stoichiometric coefficients of blanched equation. Example: calculate kc for n2 mixed with h2 at 500 c to produce ammonia. At equilibrium: n2 = 0. 305m, h2 = 0. 324m, nh3 = 0. 796m. Reverse rxn: 2nh3 n2 + 3h2. Kc = ([n2][h2]^3)/[nh3]^2 = 1/61. 0 = 0. 016. All r and p in same phases: homogeneous equilibrium. One of more r or p in different phase: heterogeneous equilibrium. Molar concentration of a pure substance (solid or liquid) does not change in a reaction. Solids and liquids not included in k expression. Example: ca(oh) ca+2 + 2 oh-

Related Questions

aA + bB ? cC + dD

where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is

Kc=[C]c[D]d / [A]a[B]b

where [A], [B], [C], and [D] are the equilibrium concentrations. If the reaction is not at equilibrium, the quantity can still be calculated, but it is called the reaction quotient, Qc, instead of the equilibrium constant, Kc.

Qc=[C]tc[D]td / [A]ta[B]tb

where each concentration is measured at some arbitrary time t.

QUESTION:

A mixture initially contains A, B, and C in the following concentrations: [A] = 0.300 M , [B] = 0.750 M , and [C] = 0.550 M . The following reaction occurs and equilibrium is established:

A+2B?C

At equilibrium, [A] = 0.120 M and [C] = 0.730 M . Calculate the value of the equilibrium constant, Kc.

Express your answer numerically.

At equilibrium, the concentrations of reactants and products can be predicted using the equilibrium constant, Kc, which is a mathematical expression based on the chemical equation. For example, in the reaction aA+bBâcC+dD where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is Kc=[C]c[D]d[A]a[B]b where [A], [B], [C], and [D] are the equilibrium concentrations. If the reaction is not at equilibrium, the quantity can still be calculated, but it is called the reaction quotient, Qc, instead of the equilibrium constant, Kc. Qc=[C]tc[D]td[A]ta[B]tb where each concentration is measured at some arbitrary time t. Part A A mixture initially contains A, B, and C in the following concentrations: [A] = 0.600 M , [B] = 1.25 M , and [C] = 0.600 M . The following reaction occurs and equilibrium is established: A+2BâC At equilibrium, [A] = 0.460 M and [C] = 0.740 M . Calculate the value of the equilibrium constant, Kc.

Very few chemical reactions go to completion. Instead, most reach a state called chemical equilibrium in which both products and reactants are present. The concentrations of reactants and products can be predicted using the equilibrium constant, Kc, which is a mathematical expression based on the chemical equation. For example, in the reaction

aA(aq)+bB(aq)âcC(aq)+dD(aq)

where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is

Kc=[C]c[D]d[A]a[B]b

Part A

A mixture initially contains A, B, and C in the following concentrations: [A]=0.600mol Lâ1, [B]=1.25mol Lâ1, and [C]=0.400mol Lâ1. The following reaction occurs and equilibrium is established:

A(aq)+2B(aq)âC(aq)

At equilibrium, [A]=0.450mol Lâ1 and [C]=0.550mol Lâ1. Calculate the value of the equilibrium constant, Kc .

CHEM 14B Lecture Notes - Lecture 1: Molar Concentration, Equilibrium Constant, Ammonia

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