[PDF] Le Chatelier’s Principle - Nc State University

Chemical Equilibrium Le Chateliers Principle

Le Chatelier's Principle Le Chatelier's principle states that when a system in chemical equilibrium is disturbed by a change in temperature, pressure, or concentration, the system will shift in equilibrium composition in a way that tends to counteract this change of variable The three ways that affect this change in equilibrium include:

Le Chatelier’s Principle - Nc State University

Le Chatelier’s Principle Description: Le Chatelier’s principle is demonstrated by either invoking a color change of anhydrous (blue) CoCl 2 or hexahydrate (pink) CoCl 2•6H 2O OR by observing the color change involved with the conversion of the chromate ion to the dichromate ion by addition of acid or base Materials:

Le Chatelier’s Principle - webgccazedu

Le Chatelier’s Principle Introduction: In this experiment you will observe shifts in equilibrium systems when conditions such as concentration and temperature are changed You will explain the observed color changes of four reactions in terms of Le Chatelier’s principle Le Chatelier predicted how an equilibrium system would respond to

Le Chateliers Principle and Buffers - Daniel Stelck

need to explain your observations using Le Chatelier's principle **USE THE SAME TEST TUBE WITHOUT POURING OUT THE TEST TUBE CONTENTS IN ALL SIX PROCEDURES IN PART I B** 1) Ag 2 CO 3 is an insoluble salt In aqueous solution: 2 Ag+(aq) + CO 3 2-(aq) Ag 2 CO 3 (s) In a small test tube add 10 drops of 0 01 M AgNO 3 to 10 drops of 0 1 M Na 2 CO 3

Le Châtelier’s Principle

Le Châtelier’s Principle According to Le Châtelier’s Principle, when a system at equilibrium is subjected to a stress (a change in concentration, temperature, or pressure), the equilibrium will shift in the direction that tends to counteract the effect of the

Le Chatelier’s Principle: Investigating the Chromate

Le Chatelier’s Principle states that “If a stress is applied to a reaction at equilibrium, the reaction will shift to offset the stress applied” The addition of hydrogen ions or hydroxide ions constitutes a stress, as does the removal of either ion, and so it can be

Properties of Systems in Equilibrium Le Châtelier’s Principle

Le Châtelier’s Principle Page 1 of 15 Properties of Systems in Equilibrium – Le Châtelier’s Principle Objectives To perturb chemical reactions at equilibrium and observe how they respond To explain these observations using Le Châtelier’s Principle To relate Le Châtelier’s Principle to the concept of coupled reactions

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A quantitative approach to Le Chatelier"s principle

Narayanan Kurur

February 11, 2009

Here we will try and give a quantitative description of yet another phenomenon which you have used extensively in a qualitative manner: the principle of Le Chatelier. It is fairly easy to show how a change in temperature or pressure affects the equilibrium value of the extent of a reaction. We need to only determine the sign of (∂ξe/∂T)pand (∂ξe/∂p)T, whereξeis the equilibrium extent of the reaction. We begin by writing the identity?∂G∂ξ T,p rG.

Because (∂G/∂ξ)T,pis itself a function ofT,p, andξ, we may write the total differential

expression, d ?∂G∂ξ =∂∂T ∂G∂ξ dT+∂∂p ∂G∂ξ dp+∂∂ξ ∂G∂ξ dξ

We will denote

∂G∂ξ byG". Using the first equation the total differential becomes d ?∂G∂ξ =?∂ΔrG∂T dT+?∂ΔrG∂p dp+G"dξ.

The temperature,

?∂G∂T p, and pressure coefficient,? ∂G∂p T are known to be-ΔSand ΔV respectively, which is is made use of now. This results in d ?∂G∂ξ =-ΔrSdT+ ΔrV dp+G"dξ. We insist that variations in temperature, pressure, and advancement of reaction all occur while keeping the reaction in equilibrium, resulting in the left hand side of the above expression being zero, because that is after all the condition for equilibrium. Moreover, at equilibrium Δ rG= 0 implying that ΔrS= ΔrH/T, so the equation becomes

0 =-?ΔrHT

(dT)eq+ ΔrV(dp)eq+G"eq(dξeq. At equilibrium, the variation ofGwithξis at a minimum which implies thatG"eqis positive.

At constant pressure,dp= 0, and hence we obtain

?∂ξ∂T p =ΔrHTG"eq. And similarly for a pressure variation at constant temperature, we have ?∂ξ∂p T =-ΔrVG"eq. These two equations are quantitative statements of the principle of Le Chatelier: they describe the dependence of the extent of the reaction at equilibrium on temperature and pressure. For example, the sign of?∂ξ∂T pdepends on the sign of ΔrHbecause, as already remarked,G" is positive at equilibrium. If the reaction is endothermic, ΔrHis positive, then an increase in temperature increases the extent of the reaction. Similarly, the sign of? ∂ξ∂p T depends on ΔrV. If ΔVis-, the product volume is less than the reactant volume and an increase in pressure shifts the equilibrium to the right because? ∂ξ∂p T is positive. The principle of Le Chatelier may thus be stated as follows: If the external constraints under which an equilibrium is established are changed, the equilibrium will shift in such a way to moderate the effect of the change. If, for example, the volume of a nonreactive system is decreased by a specified amount, the pressure rises correspondingly. In a reactive system, the equilibrium shifts to the low volume side, so the pressure increment is less than in the nonreactive case. The response of the system is moderated by the shift in equilibrium position. Similarly, if we extract a fixed quantity of heat from a nonreactive system, the tem- perature decreases by a definite amount. In a reactive system, withdrawing the same amount of heat will not produce as large a decrease in temperature because the equilib- rium shifts to the low enthalpy side. This implies that the apparent heat capacity of a reactive system is larger than that of a nonreactive one. 2quotesdbs_dbs46.pdfusesText_46