This is a full detailed chapter presenting the Mass and Energy Balances for the project’s plant of producing formaldehyde from methanol. The analysis and calculations were done manually. All process streams and unit operation were accounted for in this chapter. All required parameters from the problem statement including; conversion, selectivity, temperature, pressure and production capacity were implemented in the mass and energy balance. The following process flow diagram (PFD) of the formaldehyde plant is the reference for unit designation and stream numbering.