### 9.83

Posted:

**Tue Feb 19, 2019 9:38 pm**9.83 Hydrogen burns in an atmosphere of bromine gas to give hydrogen bromide gas. (a) What is the standard Gibbs free energy of the reaction H2(g) Br2(g) S 2 HBr(g) at 298 K? (b) If 120. mL of H2 gas at STP combines with a stoichiometric amount of bromine and the resulting hydrogen bromide dissolves to form 150. mL of an aqueous solution, what is the molar concentration of the resulting hydrobromic acid?

For part b, I tried using 1 mL = 1 g to find the moles of H2 and then the moles of HBr. I divided that by 0.150 L to find the concentration, but my answer did not match the one in the textbook. So I tried using PV=nRT to solve for the moles of H2 and I got the right answer for the concentration of HBr. Why doesn't the first method work to find the concentration of HBr?

For part b, I tried using 1 mL = 1 g to find the moles of H2 and then the moles of HBr. I divided that by 0.150 L to find the concentration, but my answer did not match the one in the textbook. So I tried using PV=nRT to solve for the moles of H2 and I got the right answer for the concentration of HBr. Why doesn't the first method work to find the concentration of HBr?