Question

The oxidation of copper(I) oxide, Cu2O(s), to copper(II) oxide, CuO(s), is an exothermic process.

2Cu2O + O2 = 4CuO

The change in enthalpy upon reaction of 85.49 g of Cu2O(s) is -87.23 kJ. Calculate the work, w, and energy change, ΔUrxn, when 85.49 g of Cu2O(s) is oxidized at a constant pressure of 1.00 bar and a constant temperature of 25 °C.

Answer in Kg.

Start by converting the mass of Cu2O that reacts (85.49 g) to the number of moles of O2 gas consumed in the reaction. Then use the ideal gas law to determine the change in volume (ΔV) during this reaction process, where Δngas is the actual amount of gas consumed. Values for R can be found at this link.

Answer 1

Cu2O molar mass = 143 g / mol

Cu2O moles = 85.49 / 143

                     = 0.598

from the baalnced equation

2 Cu2O (s) + O2 (g)-----------------------> 4 CuO (s)

2 mol               1 mol

0.598 mol        ?

gas consumed = 0.598 x 1 /2

                         = 0.299

gas moles = n = 0.299

pressure = 1 bar = ( 1/1.013 ) = 0.987 atm

P V = n RT

0.987 x V      = 0.299 x 0.0821 x 298

         V = 7. 41L

work = P V

         = 0.987 x 7.41

          = 7.31 L-atm

          = 741 J

( 1 Lit-atm = 101.32 J )

work = 741 J

internel energy :

H   = U + n RT

-87.23 x 10^3 = U +741

U = 87.97 KJ