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Chapter 17: Q40P (page 776)

(a) What is the basis of the approximation that avoids using the quadratic formula to find an equilibrium concentration?

(b) When should this approximation not be made?

Short Answer

Expert verified
  1. When K is small, and the initial concentration is big, the approximation applies when the shift in concentration from initial to equilibrium concentration is so comparable that it is inconsequential.
  2. When the change in concentration is higher than 5%, the approximation should not be employed. This can happen when very tiny or when [reactant] changes dramatically due to a big K.

Step by step solution

01

Step 1: (a) What is the basis of the approximation?

When performing chemical calculations, we are usually concerned with employing the most precise data and formulae to arrive at a satisfactory result. However, there are situations whenapproximations are warranted to make computations easier or even practicable.

Theapproximationapplies when the change in concentration from initial to equilibrium concentration is so similar that it is insignificant. This occurs when K is small, and the initial concentration is large.

02

(b) When should this approximation not be made?

The approximation should not be used when the change in concentration is greater than 5%. This can occur when Reachantinitialis very small or when the change in is relatively large due to large K.

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Most popular questions from this chapter

The following reaction can be used to make H2for the synthesis of ammonia from the greenhouse gases carbon dioxide and methane:

CH4(g)+CO2(g)⇌2CO(g)+2H2(g)

(a) What is the percent yield of H2 when an equimolar mixture of CH4and CO2with a total pressure of 20.0 atm reaches equilibrium at 1200. K, at which Kp=3.548×106?

(b) What is the percent yield of H2for this system at 1300. K, at which Kp=2.626×107?

(c) Use the van’t Hoff equation to find ∆Hrxn0 .

A gaseous mixture of 10.0 volumes ofrole="math" localid="1656949069888" CO2,1.00 volume of unreacteddata-custom-editor="chemistry" O2 , and50.0 volumes of unreactedN2 leaves an engine at4.0atm and 800K. Assuming that the mixture reaches equilibrium, what are

(a) the partial pressure and

(b) The concentration (in picograms per litre,pg/L ) ofdata-custom-editor="chemistry" CO in this exhaust gas?data-custom-editor="chemistry" 2CO2(g)⇌2CO(g)+O2(g)   Kp=1.4×10−28 atdata-custom-editor="chemistry" 800. K (The actual concentration ofdata-custom-editor="chemistry" CO in exhaust gas is much higher because the gases do not reach equilibrium in the short transit time through the engine and exhaust system.)

When ammonia is made industrially, the mixture of N2,H2, anddata-custom-editor="chemistry" NH3 that emerges from the reaction chamber is far from equilibrium. Why does the plant supervisor use reaction conditions that produce less than the maximum yield of ammonia?

Balance each of the following examples of heterogeneous()

equilibria and write its reaction quotient, Qc:

(a)H2O(I)+SO3(g)𝆏H2SO4(aq)(b)KNO3(s)𝆏KNO2(s)+O2(g)(c)S8(s)+F2(g)𝆏SF6(g)

Is K very large or very small for a reaction that goes essentially to completion? Explain.
See all solutions

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