I would really appreciate some help with this thermochemistry problem! I'm really confused as to why I keep getting the wrong answers... I have gotten w=-1.305kj and energy change = 78.13kj... both of which were marked wrong. Here's the question:

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.

Additional Details
Useful equations
Ideal Gas: PV = nRT
Work: w = –PΔV
Energy Change: ΔUrxn = ΔHrxn – PΔV

Thank you in advance! :)

If you had shown your work perhaps could have found the error. When you did pdV did you leave that in L*atm or did you convert that to kJ? Why not wshow your work and let us look at it?

To solve this problem, we need to calculate the work (w) and energy change (ΔUrxn) using the given information and the equations provided.

Let's start with the equation for work (w):

w = -PΔV

The first step is to calculate the change in volume (ΔV). In this case, since the reaction is happening at a constant pressure, we can assume the change in volume is equal to the change in moles (Δn) multiplied by the molar volume (V). The molar volume is given by the ideal gas equation, but we need to calculate the moles first.

To calculate the moles, we can use the molar mass of Cu2O. The molar mass of Cu2O is calculated by adding the atomic masses of copper (Cu) and oxygen (O) together. The atomic mass of Cu is 63.55 g/mol and the atomic mass of O is 16.00 g/mol. Since there are 2 moles of Cu in Cu2O and 1 mole of O, the molar mass of Cu2O is:

63.55 g/mol * 2 + 16.00 g/mol = 143.10 g/mol

Next, we can use the given mass of Cu2O (75.30 g) to calculate the moles:

moles = mass / molar mass
moles = 75.30 g / 143.10 g/mol ≈ 0.526 moles

Since the stoichiometric coefficient of Cu2O is 2 in the balanced equation, the change in moles (Δn) is 2 * 0.526 = 1.052 moles.

Now, we can calculate the change in volume (ΔV) by multiplying Δn by the molar volume (V). The molar volume can be calculated using the ideal gas equation:

PV = nRT

Given:
P = 1.00 bar = 1.00 * 10^5 Pa (since 1 bar = 10^5 Pa)
n = 1.052 moles
R = 8.314 J/(mol·K) (ideal gas constant)
T = 25°C = 298 K (since temperature needs to be in Kelvin)

Rearranging the ideal gas equation, we get:

V = nRT / P
V = (1.052 mol) * (8.314 J/(mol·K)) * (298 K) / (1.00 * 10^5 Pa)
V ≈ 2.505 * 10^-2 m^3

Now that we have the change in volume (ΔV), we can calculate the work (w):

w = -PΔV
w = -(1.00 * 10^5 Pa) * (2.505 * 10^-2 m^3)
w ≈ -2.505 kJ

Therefore, the work (w) is approximately -2.505 kJ.

Next, let's calculate the energy change (ΔUrxn) using the given ΔHrxn (change in enthalpy):

ΔUrxn = ΔHrxn - PΔV
ΔUrxn = -76.83 kJ - (-1.00 * 10^5 Pa) * (2.505 * 10^-2 m^3)
ΔUrxn ≈ -76.83 kJ - (-2.505 kJ)
ΔUrxn ≈ -74.32 kJ

Therefore, the energy change (ΔUrxn) is approximately -74.32 kJ.

I hope this explanation helps you understand how to solve the problem and get the correct answers. If you have any further questions, feel free to ask!