Find mass of product when given Kc, mass of reactant, but not volume

In summary, to determine the mass of methylcyclopentane present in an equilibrium mixture with cyclohexane at 25 C, we can use the equilibrium constant (Kc = 0.143) to calculate the ratio of product to reactant. Since the volume and mass of the solution do not matter, we can equate the initial and final moles and masses of cyclohexane and methylcyclopentane. Using the molecular mass of both compounds, we can then calculate the percentage of cyclohexane that is converted into methylcyclopentane. The given reaction equation, C6H12 <=> C5H9CH
  • #1
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Homework Statement


Assume that at 25 C, with AlCl3 as a catalyst, the following equilibrium can be established between the liquids cyclohexane and methylcyclopentane.
C6H12 <=> C5H9CH3HCH3
Kc = 0.143
If initially 1.00 x 10^2 g cyclohexane is present, what mass of methylcyclopentane will be present in the equilibrium mixture? (Hint: Does the volume of solution matter?)

Homework Equations



Kc = [product]/[reactant]

The Attempt at a Solution


I attempted to use ICE, but since I do not know the concentration (M) for the reactants, I do not know how to proceed.
I could get the moles of cyclohexane, but then don't I need to convert it to M?

Please advice. Thank you in advance.
 
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  • #2
HINT: Does the Volume matter?
HINT2 : Does the mass matter? In a more abstract kinda way?

The thing is :

- moles initially of molecules (Cyclohex) = moles finally (Cyclohex + metpent)
- mass initially = mass finally
- and obviously Molecular mass of hex = Mol mass of pent
Kc=mass pentane/mass hexane=moles pentane/moles hexane.

So you end up with the amount % of hex that gets turned into pent.
 
  • #3
Btw what is that:
C6H12 <=> C5H9CH3HCH3

the second isn't metylcyclopentane
 

What is Kc?

Kc, also known as the equilibrium constant, is a ratio of the concentrations of products to reactants at a specific point in a reaction. It is used to determine the direction and extent of a chemical reaction.

How do you calculate the mass of product?

The mass of product can be calculated by using the given Kc value and the mass of the reactant. First, calculate the concentration of the reactant using its mass and volume. Then, use the Kc value and the concentration of the reactant to calculate the concentration of the product. Finally, use the concentration of the product and its molar mass to calculate the mass of the product.

Why is the volume not given?

In some cases, the volume of the reactant may not be provided because it is not necessary for the calculation of the mass of the product. The volume may also be assumed to be constant or not significantly affect the outcome of the calculation.

What units should be used for Kc and the mass of the reactant?

Kc is a unitless quantity, as it is a ratio of concentrations. The mass of the reactant should be in grams for consistency in the calculation.

What are some limitations of using Kc to calculate the mass of product?

Kc is only applicable to reactions at equilibrium, so it may not accurately predict the mass of product at other points in the reaction. Additionally, other factors such as temperature and pressure can also affect the mass of product, which Kc does not account for.

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