As an AI language model, I am unable to perform quantum chemical calculations directly. However, I can guide you through the process of calculating the standard enthalpy of formation for CO2 using quantum chemical methods.1. Choose a quantum chemical method: First, you need to choose a suitable quantum chemical method to perform the calculations. Some popular methods include Hartree-Fock HF , Density Functional Theory DFT , and post-Hartree-Fock methods like Mller-Plesset perturbation theory MP2 or Coupled Cluster CC . The choice of method depends on the desired accuracy and computational resources available.2. Select a basis set: Next, you need to choose an appropriate basis set for your calculations. Basis sets are mathematical representations of atomic orbitals. Some common basis sets include STO-3G, 6-31G, and cc-pVDZ. The choice of basis set depends on the desired accuracy and computational resources available.3. Perform geometry optimization: Before calculating the enthalpy of formation, you need to find the equilibrium geometry of the CO2 molecule. This can be done by performing a geometry optimization using the chosen quantum chemical method and basis set.4. Calculate the energy of CO2: Once you have the optimized geometry, you can calculate the total energy of the CO2 molecule using the chosen quantum chemical method and basis set.5. Calculate the energy of the constituent elements: To determine the enthalpy of formation, you also need to calculate the energy of the constituent elements in their standard states. For CO2, this means calculating the energy of an isolated carbon atom in its ground state and an isolated oxygen molecule O2 in its ground state.6. Calculate the standard enthalpy of formation: The standard enthalpy of formation for CO2 can be calculated using the following equation:Hf CO2 = E CO2 - [E C + 1/2 E O2 ]where Hf CO2 is the standard enthalpy of formation for CO2, E CO2 is the energy of the CO2 molecule, E C is the energy of an isolated carbon atom, and E O2 is the energy of an isolated oxygen molecule.7. Convert the energy to the desired units: The energy values obtained from quantum chemical calculations are usually in atomic units Hartree . To convert the enthalpy of formation to more common units like kJ/mol, you can use the following conversion factor:1 Hartree = 2625.50 kJ/molAfter following these steps, you should have the standard enthalpy of formation for CO2 using quantum chemical calculations. Keep in mind that the accuracy of the result depends on the chosen method and basis set.