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.
Still confused...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...
Thanks
Isn't that constant 8.314 and not 0.08314 so you end up with +0.6523 kJ for the work?
Let me know how this turns out.
To calculate the work, w, we need to use the formula:
w = -ΔnRT
where:
Δn is the change in the number of moles of gas,
R is the ideal gas constant (8.314452 J/(mol·K)),
T is the temperature in Kelvin.
In the given reaction,
2 Cu2O + O2 → 4 CuO,
we can see that there is no change in the number of moles of gas, as both the reactant and product have no gas molecules involved. Therefore, Δn = 0.
Now, let's calculate the work, w:
w = -(0) * (8.314452 J/(mol·K)) * (25 + 273.15) = 0
So, the work, w, is 0 J.
For the energy change, ΔUrxn, you had already calculated it correctly as -76.82 kJ.
Therefore, when 75.30 g of Cu2O(s) is oxidized under the given conditions, the work done, w, is 0 J and the energy change, ΔUrxn, is -76.82 kJ.
To calculate the work, w, and energy change, ΔUrxn, when 75.30 g of Cu2O(s) is oxidized, you need to use the equation w = -ΔnRT and ΔUrxn = q + w, where Δn is the change in the number of moles of gas involved in the reaction, R is the gas constant, T is the temperature in Kelvin, q is the heat exchanged during the reaction, and w is the work done during the reaction.
Let's start by calculating Δn. The given reaction is 2 Cu2O + O2 → 4 CuO. We can see that the number of moles of gas decreases from 1 mole of O2 to 0 moles of O2. Therefore, Δn = 0 - 1 = -1.
Next, convert the mass of Cu2O to moles. The molar mass of Cu2O is 143.09 g/mol. So, 75.30 g of Cu2O is equal to 75.30 g / 143.09 g/mol = 0.5256 mol.
Now, calculate the work, w. Use the given conditions of constant pressure (1.00 bar) and the temperature of 25°C, which is equal to 298.15 K.
w = -ΔnRT = -(0 - 1) × (8.314452x10^-2 L bar/mol K) × (298.15 K) = 24.519 L bar = 24.519 J
Note that the unit for gas constant R is L bar/mol K, and the unit for work is J (Joules).
Now, convert the work from J to kJ by dividing by 1000:
w = 24.519 J / 1000 = 0.024519 kJ
Finally, calculate the energy change, ΔUrxn, using ΔUrxn = q + w.
Given that ΔUrxn = -76.83 kJ (from the question), we can rearrange the equation to solve for q:
q = ΔUrxn - w = -76.83 kJ - 0.024519 kJ = -76.854519 kJ.
So, the energy change, ΔUrxn, when 75.30 g of Cu2O(s) is oxidized is approximately -76.854519 kJ.
To summarize, the correct values are:
- Work, w = 0.024519 kJ
- Energy change, ΔUrxn = -76.854519 kJ