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Degree of dissociation (alpha) alpha a...

Degree of dissociation `(alpha)`
`alpha` are the number of moles which are dissociating from 1 mole of given reactants and gas density measurements can be used to determine the degree of dissociatin. Let us take a general case where one molecule of a substance A splits up into n molecules of A(g) on heating i.e.,
`A_(n)(g)hArrnA(g)`
`t=0a`
`t =t_(eq)a-x nx " "alpha=x/aimpliesx=a alpha`
`a-a alpha n a alpha`
Total number of Moles `=a-a alpha +n a alpha`
`=[1+(n-1)alpha]a`
Observed molecular weight of molar mass of the mixture
`M_("mixture")=(M_(A_(n)))/([1+(n-1)alpha]),M_(A_(n))=` Molar mass of `A_(n)`
A sample of mixture A(g), B(g)and C(g) under equlibrium has a mean molecular weight (observed) of 80.
The equlibrium is
`A(g)hArrB(g)+C(g)`
(Mol wt =100)`" "` (Mol. wt=60)`" "` (Mol. wt=40) Calculate the Degree of dissociation for given reaction.

A

`0.25`

B

`0.5`

C

`0.75`

D

`0.8`

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The correct Answer is:
A
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For certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. the measured densities are found to be less than those calculated from their molecular formula.The observed densities decreases towards a limit as the temperature is raised.This is due to the splitting of the molecular into simpler ones.The process is reversible and is called thermal dissociation. Example : NH_4Cl hArr NH_3+HCl I_2hArr 2I N_2O_4 hArr 2NO_2 PCl_5hArr PCl_3+Cl_2 With increase in the number of molecules, the volume increases (pressure remaining constant) and in consequence, the density decreases.As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occurs the density reaches its lowest limit. The extent of dissociation, i.e., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation.Gas density measurements can be used to determine the degree of dissociation.Let us take by general case where one molecule of a substance A splits up into n molecule of A on heating , i.e., A_n(g)hArr nA(g) t=0 " "a" " 0 t=t_(eq) a-x n.x alpha=x/a rArr x=a alpha. a-a alpha naalpha Total no. of moles = a-a alpha+n a alpha = [1+(n-1)alpha]a Observed molecular weight or molar mass of the mixture M_("mixture")=M_(A_(n))/([1+(n-1)alpha]), M_(A_(n)) =Molar mass of gas A_n x(degree of dissociation) varies with D/d in the above reaction according to :

Knowledge Check

  • Degree of dissociation (alpha) alpha are the number of moles which are dissociating from 1 mole of given reactants and gas density measurements can be used to determine the degree of dissociatin. Let us take a general case where one molecule of a substance A splits up into n molecules of A(g) on heating i.e., A_(n)(g)hArrnA(g) t=0a t =t_(eq)a-x nx " "alpha=x/aimpliesx=a alpha a-a alpha n a alpha Total number of Moles =a-a alpha +n a alpha =[1+(n-1)alpha]a Observed molecular weight of molar mass of the mixture M_("mixture")=(M_(A_(n)))/([1+(n-1)alpha]),M_(A_(n))= Molar mass of A_(n) If the t otal mass of the mixture in question (1) is 300 gm, then moles of C(g) present are

    A
    `1/4`
    B
    `4/3`
    C
    `3/4`
    D
    `1/2`

  • For certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. the measured densities are found to be less than those calculated from their molecular formula.The observed densities decreases towards a limit as the temperature is raised.This is due to the splitting of the molecular into simpler ones.The process is reversible and is called thermal dissociation. Example : NH_4Cl hArr NH_3+HCl I_2hArr 2I N_2O_4 hArr 2NO_2 PCl_5hArr PCl_3+Cl_2 With increase in the number of molecules, the volume increases (pressure remaining constant) and in consequence, the density decreases.As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occurs the density reaches its lowest limit. The extent of dissociation, i.e., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation.Gas density measurements can be used to determine the degree of dissociation.Let us take by general case where one molecule of a substance A splits up into n molecule of A on heating , i.e., A_n(g)hArr nA(g) t=0 " " a " " 0 t=t_(eq) a-x n.x alpha=x/a rArr x=a alpha. a-a alpha naalpha Total no. of moles = a-a alpha+n a alpha = [1+(n-1)alpha]a Observed molecular weight or molar mass of the mixture M_("mixture")=M_(A_(n))/([1+(n-1)alpha]), M_(A_(n)) =Molar mass of gas A_n A sample of mixture of A(g),B(g) and C(g) under equilibrium has a mean molecular weight (observed ) is 80. The equilibrium is underset((mol.wt.=100))(A(g))hArrunderset((mol.wt.=60))(B(g))+underset((mol.wt.=40))(C(g)) Find the degree of dissociation alpha for A(g)

    A
    `0.25`
    B
    `0.5`
    C
    `0.75`
    D
    `0.8`

  • For certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. the measured densities are found to be less than those calculated from their molecular formula.The observed densities decreases towards a limit as the temperature is raised.This is due to the splitting of the molecular into simpler ones.The process is reversible and is called thermal dissociation. Example : NH_4Cl hArr NH_3+HCl I_2hArr 2I N_2O_4 hArr 2NO_2 PCl_5hArr PCl_3+Cl_2 With increase in the number of molecules, the volume increases (pressure remaining constant) and in consequence, the density decreases.As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occurs the density reaches its lowest limit. The extent of dissociation, i.e., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation.Gas density measurements can be used to determine the degree of dissociation.Let us take by general case where one molecule of a substance A splits up into n molecule of A on heating , i.e., A_n(g)hArr nA(g) t=0 " " a" " 0 t=t_(eq) a-x n.x alpha=x/a rArr x=a alpha. a-a alpha naalpha Total no. of moles = a-a alpha+n a alpha = [1+(n-1)alpha]a Observed molecular weight or molar mass of the mixture M_("mixture")=M_(A_(n))/([1+(n-1)alpha]), M_(A_(n)) =Molar mass of gas A_n If the total mass of a mixture in the above case is 300 gm, the moles of C(g) present are.

    A
    `1/4` mole
    B
    `4/3` mole
    C
    `3/4` mole
    D
    None

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    For certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. the measured densities are found to be less than those calculated from their molecular formula.The observed densities decreases towards a limit as the temperature is raised.This is due to the splitting of the molecular into simpler ones.The process is reversible and is called thermal dissociation. Example : NH_4Cl hArr NH_3+HCl I_2hArr 2I N_2O_4 hArr 2NO_2 PCl_5hArr PCl_3+Cl_2 With increase in the number of molecules, the volume increases (pressure remaining constant) and in consequence, the density decreases.As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occurs the density reaches its lowest limit. The extent of dissociation, i.e., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation.Gas density measurements can be used to determine the degree of dissociation.Let us take by general case where one molecule of a substance A splits up into n molecule of A on heating , i.e., A_n(g)hArr nA(g) t=0 " " a" " 0 t=t_(eq) a-x n.x alpha=x/a rArr x=a alpha. a-a alpha naalpha Total no. of moles = a-a alpha+n a alpha = [1+(n-1)alpha]a Observed molecular weight or molar mass of the mixture M_("mixture")=M_(A_(n))/([1+(n-1)alpha]), M_(A_(n)) =Molar mass of gas A_n The K_P for the reaction N_2O_4 hArr 2NO_2 is 640 mm at 775 K.The percentage dissociation of N_2O_4 at equilibrium pressure of 160 mm is :

    For certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. the measured densities are found to be less than those calculated from their molecular formula.The observed densities decreases towards a limit as the temperature is raised.This is due to the splitting of the molecular into simpler ones.The process is reversible and is called thermal dissociation. Example : NH_4Cl hArr NH_3+HCl I_2hArr 2I N_2O_4 hArr 2NO_2 PCl_5hArr PCl_3+Cl_2 With increase in the number of molecules, the volume increases (pressure remaining constant) and in consequence, the density decreases.As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occurs the density reaches its lowest limit. The extent of dissociation, i.e., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation.Gas density measurements can be used to determine the degree of dissociation.Let us take by general case where one molecule of a substance A splits up into n molecule of A on heating , i.e., A_n(g)hArr nA(g) t=0" " a" " 0 t=t_(eq) a-x n.x alpha=x/a rArr x=a alpha. a-a alpha naalpha Total no. of moles = a-a alpha+n a alpha = [1+(n-1)alpha]a Observed molecular weight or molar mass of the mixture M_("mixture")=M_(A_(n))/([1+(n-1)alpha]), M_(A_(n)) =Molar mass of gas A_n The equation alpha=(D-d)/((n-1)d) is correctly matched for :

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