help - confusion :(
The oxidation of copper(I) oxide, Cu2O(s), to copper(II) oxide, CuO(s), is an exothermic process,
2 Cu2O + O2 --> 4CuO
The change in enthalpy upon reaction of 75.30 g of Cu2O(s) is -76.83 kJ. Calculate the work, w, and energy change, ΔUrxn, when 75.30 g of Cu2O(s) is oxidized at a constant pressure of 1.00 bar and a constant temperature of 25°C.
Here's my line of reasoning.. but it's been marked wrong. Thank you in advance.
converting 75.3g of Cu2O to moles of CuO, I got 1.0525mol CuO
W=-delta(n)RT = -(1.0525mol)(8.3144J/molK)(25+273.15)= -2.609 kJ
energy change = -2.609kj+ - 76.83kJ = -79.439kJ
the heat of reaction is 76.83kJ per mole of Cu2O, not CuO.
Then, work=moles*Cu2O*76.83kJ
and that is it. Your delta(n)RT is off the thinking mark.
You appear to be calculating the change in volume from mols Cu2O ==> 2CuO. But each is a solid and they don't count do they? Isn't the change in volume the change due to the gas which is oxygen? Shouldn't you calculate how much oxygen was there initially and how much is there at the end (zero of course) and p*delta V then is the work done by the surroundings on the system. The mols O2 you can calculate from mols Cu2O given in the problem.
ok I recalculated and got the w=.006523kJ and the energy change to be -76.82kJ... The energy change is right but the w is wrong for some reason...
I calculated w as w=-delta(n)RT = -(0-.26312molO2)(8.314452x10^-2 Lbarr/molK)(25+273.15) = 6.5226J=.006523kJ...
The oxidation of copper(I) oxide, Cu2O(s) , to copper(II) oxide, CuO(s) , is an exothermic process.
2Cu2O(s)+O2(g)⟶4CuO(s)
The change in enthalpy upon reaction of 70.64 g Cu2O(s) is −72.08 kJ .
Calculate the work, 𝑤 , and energy change, Δ𝑈rxn , when 70.64 g Cu2O(s) is oxidized at a constant pressure of 1.00 bar and a constant temperature of 25∘ C .
Note that Δ𝐸rxn is sometimes used as the symbol for energy change instead of Δ𝑈rxn .
im confused
I understand that you're trying to calculate the work, w, and energy change, ΔUrxn, for the oxidation of copper(I) oxide. Let's go through the steps and see where the error might be.
First, let's calculate the moles of CuO produced from 75.30 g of Cu2O. You mentioned that you got 1.0525 mol of CuO, which is correct.
Now, let's calculate the work, w. The equation you provided, W = -ΔnRT, is correct, where Δn is the change in the number of moles of gas during the reaction, R is the gas constant (8.3144 J/molK), and T is the temperature in Kelvin.
Since the reaction involves 2 moles of Cu2O reacting to form 4 moles of CuO, the change in the number of moles of gas, Δn, is zero. This is because the number of moles of gas remains the same before and after the reaction. Therefore, the work, w, in this case, would be zero.
Next, let's calculate the energy change, ΔUrxn. You correctly found the change in enthalpy to be -76.83 kJ. However, when adding the work and change in enthalpy, you made a calculation error.
The correct calculation is:
Energy change = work + change in enthalpy
Energy change = 0 kJ + (-76.83 kJ)
Energy change = -76.83 kJ
So, the correct energy change, ΔUrxn, when 75.30 g of Cu2O is oxidized at a constant pressure of 1.00 bar and a constant temperature of 25°C, is -76.83 kJ.
Please double-check your calculations and ensure all units are consistent.