Question

Iron reacts with oxygen in the air to form rust. Predict the signs of enthalpy, entropy, and Gibbs free energy change for this process (for the system). Explain the sign for each one

Answer 1

4Fe + 3O2 —> 2Fe2O3

enthalpy will be negative as this is an oxidation process and all oxidation process has negative enthalpy (releasing energy that’s why we feel the heat)

entropy will be negative as we can see in the equation the reactants are 4 molecules of solid (Fe) and 3 molecules of gas (O2) but the product is only 2 molecules of solid which has lower entropy, hence the net entropy is negative

Gibbs free energy will depend on the temperature. at higher temperature the gibbs will be negative