The objective of the present paper is to examine numerically the chemical reaction and mass transfer effects on magnetohydrodynamic Williamson fluid past an exponentially stretching sheet. The basic flow field equations are transformed to coupled, nonlinear ordinary differential equations using suitable similarity variables and then solved using the Runge–Kutta–Fehlberg method. The effects of various material parameters on the flow field momentum and species in addition to wall shear stress are computed effectively and portrayed graphically. The diffusion rate is low for both homogeneous and heterogeneous reactions. Acceleration in the values of Williamson fluid parameters accelerates the friction. © Springer Nature Switzerland AG 2019.