Calculating Percentage of Dissociated N2O4 Molecules: Vapour Density Question

In summary, the question asks what percentage of N2O4 molecules dissociate into NO2 gas when the vapour density of the sample is 35. Using the equation molar mass = 2 * vapour density, the mass of N2O4 in the sample can be calculated. To find the degree of dissociation, the initial number of moles of N2O4 can be compared to the number of moles after dissociation. The observed molar mass is a weighted average of the molar masses of the components.
  • #1
navneet9431
Gold Member
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Homework Statement


The vapour density of a sample of N2O4 gas is 35. What per cent of N2O4 molecules are dissociated inNO2?

Homework Equations


molar mass = 2 * Vapour Density

The Attempt at a Solution


I tried to solve this question this way,
Let the initial number of moles of N2O4=a
and, assume that the degree of dissociation is α
So,the reaction would be

N2O4 ---------> 2NO2
a ---------------0 (Before Dissociation)
a(1-α)------------2aα (After-dissociation)

And also since VD of N2O4 gas is 35. So,the mass of N2O4 gas would be=35*2=70.
But i do not know what i shall do next?
I will be thankful for any help!
 
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  • #2
navneet9431 said:
molar mass = 2 * Vapour Density

Hint: observed molar mass is a weighted average of the molar masses of components.
 

1. How do I calculate the percentage of dissociated N2O4 molecules?

To calculate the percentage of dissociated N2O4 molecules, you will need to know the vapour density of the sample and the molecular weight of N2O4. The formula for percentage dissociation is (% dissociation = (1 - (vapour density/N2O4 molecular weight)) x 100).

2. What is the significance of calculating the percentage of dissociated N2O4 molecules?

Calculating the percentage of dissociated N2O4 molecules is important in understanding the equilibrium of a chemical reaction. It can also provide information about the stability of the substance and its potential for decomposition.

3. How do I determine the vapour density of a sample?

The vapour density of a sample can be determined by measuring the mass of the sample and the volume it occupies under specific conditions, such as constant temperature and pressure. Then, using the ideal gas law (PV = nRT), you can calculate the vapour density by dividing the mass of the sample by the product of the volume, number of moles, and gas constant.

4. Can the percentage of dissociated N2O4 molecules change over time?

Yes, the percentage of dissociated N2O4 molecules can change over time as the reaction reaches equilibrium. The percentage of dissociation will depend on factors such as temperature, pressure, and the presence of catalysts.

5. How does the percentage of dissociated N2O4 molecules affect the vapour pressure of the sample?

The percentage of dissociated N2O4 molecules directly affects the vapour pressure of the sample. As more N2O4 molecules dissociate, the number of gaseous molecules in the sample increases, resulting in a higher vapour pressure. This relationship can be described by the Le Chatelier's principle, which states that an increase in the number of gaseous molecules in a system will lead to an increase in pressure.

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