1. A method to crack a gaseous hydrocarbon comprising passing the hydrocarbon through a reactor having a reduced calculated pressure drop across a flow path having a continuously smooth and differentiable perimeter and centerline of one or more first straight pipe sections of a serpentine reactor by not less than 10% relative to a second pipe section having a flow path having an ARQ from 1.0 to 1.02 where ARQ is defined as the ratio of aspect ratio (AR) to isoperimetric quotient (Q) of a section or segment of the flow passage perpendicular to the direction of flow (AR/Q) and further where AR=Long/short and Q = 4 ⁢ π ⁢ ⁢ A L 2 where A is area of a cross section of the flow path and L is the perimeter of the flow path comprising varying the flow passage over 90% of its length from 5% from the inlet and outlet so that the ARQ is from about 1.02 to about 1.15 at a temperature from 850° C. to 1000° C.