What are the Mass and Empirical Formula of the Combusted Hydrocarbon?

[fabrave21]

2 question I don't get ... =\ any help would be appreciated.
I don't even know where to start ...

Homework Statement

2. A sample of a hydrocarbon is combusted completely in O2 to produce 21.83 g CO2, 4.47 g H2O and 311 kJ of heat. A) What is the mass of the hydrocarbon sample that was combusted? B) What is the empirical formula of the hydrocarbon? C) Calculate the value of ΔHfº per empirical-formula unit of the hydrocarbon.7. Suppose you have some reaction: 2A ---> B and B ---> 2A The rate for the formation of B from A is 3.8 x 102 s-1 and the rate for the formation of A from B is 8.6 x 10-1 s-1. A) What is the equilibrium constant for the equilibrium reaction, 2A <----> B ?
B) Suppose that you started with 2 moles of A and at some later time you measure .9 moles of B in a total volume of 1L, is the reaction at equilibrium? Explain.

Homework Equations

The Attempt at a Solution

2. mols C = 21.83/44 =.496

mols H = 4.47/18.0 =,248 x2 =.496

mols = g/Mwt then mols x Mwt = g

The mass of C is .496 x12.0 = .5.97 g C
The mass of H = .496 x 1.00 = ,496 g H
Total mass is 6.47 g for the hydrocarbon

The empirical formula is the ratio of the mols of C and H which makes it C1H1

6.47/ 13 = .496 mols
heat of combustion per formula weight is 311KJ/ .498 mols

= 624.497992 kJ

7. ?

 

[fabrave21]

figured out number 2. Still don't get number 7

 

[Borek]

Have you heard about kinetic intepretation of equilibrium?

Write expressions for
- reaction equilibrium
- forward reaction speed
- backward reaction speed

Compare denominator with forward reaction speed and denominator with backward reaction speed. Do you think you can combine rate coefficients to get equilibrium constnats?