Help with Chemistry Problem PLEASE!?

Question

Calculate moleculer formulas of the compounds having the following empirical formulas and molar masses: C2H8, 58 g/mol;CH, 78 g/mol; HgCl 236.1

and then this one also

Assuming STP and a stoichiometric amount of NH3 and NO in an expandable container originally at 15 L, what is the final volume if the reaction goes to completion? 4NH-3+6NO --> 5N-2 + 6H-2O

Answer 1

I think you meant to say C2H5 in your first problem.

How much does C2H5 weigh?

C = 12 x 2 = 24
H = 1 x 5 = 5
24 + 5 = 29

If the empirical formula mass is 29 and the actual molar mass is twice as much (58) then the molecular formula must be twice as much as the empirical formula, or C4H10.

CH has a mass of 13

Therefore if the mass is 78, then 78/13 = 6

The molecular formula must be six times the empirical formula, or C6H6

HgCl has a mass of 236.1 so that IS the molecular formula, HgCl

A stoichiometric amount means that there are the exact molar ratios you need, with nothing left over. In the balanced equation, you go from 10 moles of gaseous reactants to 11 moles of gaseous products. Therefore the ratio of products to reactants must be 11 to 10.
Final volume would be 15 L x (11/10) = 16.5 L

Answer 2

For the first part, calculate the molecular mass of each empirical formula. Compare this to the true molecular mass ans see how many units of the EF are inlcuded. That will give you the Molecular formula.

For example, CH and 78 g/mol.

The mass of CH is 13. There are 6 units of 13 in 78. So the molecular formula is C6H6. You can easily do the others.

For your second problem, use the ideal law PV=nRT.
You sart with 9 moles of gas in 15 L. You finish with 11 moles of gas. ALl else remians the same. Use a simple ratio to get the new volume