Thermodynamic approach to foresee experimental CO2 reduction to organic compounds

•The potential procurement of elongated compounds from CO2 was studied and tested.•The thermodynamic analysis revealed ethanol was the bottleneck for chain elongation.•Experimental tests allowed fine-tuning of the operating conditions.•The integration of thermodynamics and biology intensified caproic acid production.•The highest caproic acid titter (>11 g L−1) was obtained from simple substrates.