Question

Hydrogen peroxide decomposes into water and oxygen according to the following reaction: 2H2O2(1)→ 2H2O(g) + O2(g) 0.11 g of H2O2 is decomposed in a flask with a volume of 2.50 L. What is the pressure of O2 at 298 K? a. 0.032 atm b. 0.048 atm C. 0.016 atm d. 0.16 atm e. None of the above Predict the signs of AH° and ASº for the following reaction: O2(g) + O2(1) a. + AH°; + AS° b. + AH°; - AS° C. - AH° ; + AS° d. - AH°; - AS° e. None of the above

Answer 1

1)

Molar mass of H2O2,

MM = 2*MM(H) + 2*MM(O)

= 2*1.008 + 2*16.0

= 34.016 g/mol

mass of H2O2 = 0.11 g

mol of H2O2 = (mass)/(molar mass)

= 0.11/34.02

= 3.234*10^-3 mol

According to balanced equation

mol of O2 formed = (1/2)* moles of H2O2

= (1/2)*3.234*10^-3

= 1.617*10^-3 mol

Given:

V = 2.50 L

n = 1.617*10^-3 mol

T = 298 K

use:

P * V = n*R*T

P * 2.5 L = 0.0016 mol* 0.08206 atm.L/mol.K * 298 K

P = 0.016 atm

Answer: c

2)

Gas is changing to liquid.

So, heat must be released.

So, ΔHo is negative.

Reactant has more entropy than product because of presence of gas in reactant.

So, ΔSo is negative

Answer: d