Question

For the ethylene combustion reaction

C₂H₄ + 3O₂ ! 2CO₂ + 2H₂O,
assume that all reactants and products are gases. For one mole of ethylene, estimate the magnitude of the P V work done at constant pressure and determine whether the work is done on the system or on the surroundings.
Assume a room temperature of 300 K.

Answer 1

To estimate the PV work done during the combustion of one mole of ethylene at constant pressure, one would use the equation Δ(nRT). However,

Step-by-step explanation:

The student is asking how to estimate the magnitude of the PV work done during the combustion of one mole of ethylene (C2H4) at constant pressure and whether the work is done on the system or on the surroundings, given the reaction is C2H4 + 3O2 → 2CO2 + 2H2O, at room temperature (300 K).

For this reaction, there is a decrease in the number of moles of gas: from 4 moles on the reactant side (1 mole of ethylene and 3 moles of oxygen) to 4 moles of gas on the product side (2 moles of carbon dioxide and 2 moles of water vapor).

If the reaction occurs at constant pressure, then the work done can be estimated using the equation Δ(nRT) as work (w) is equal to –PΔV, where ΔV is the change in volume, P is the pressure, n is the number of moles, R is the ideal gas constant, and T is the temperature. Since there is no change in moles, Δ(nRT) would be zero, meaning no work is done on or by the system. In a scenario with a change in moles, work would be done by the system if moles decreased (expansion) and on the system if moles increased (compression).