The general equivalence principle of Tacina & Dahm (2000) (Part 1) that extends scaling laws for non-reacting flows to account for density changes due to reaction heat release is applied to turbulent mixing layers to develop physically based scaling laws for heat release effects in exothermic reacting mixing layers. This leads to an ‘extended density ratio’ $s^+$ based on the equivalent elevated temperature for one of the two free-stream fluids that accounts for the density variations within the layer due to exothermic reaction. When used in place of the isothermal density ratio $s$ in scaling laws for growth rate and entrainment ratio in non-reacting mixing layers, resulting predicted effects of heat release show good agreement with measured values, and reveal subtle effects of stoichiometry previously unnoticed in experiments. Results also suggest ways to achieve increased growth rates and entrainment ratios due to heat release in turbulent mixing layers. These results for heat release effects in mixing layers, and earlier results for heat release effects in the near and far fields of planar and axisymmetric jets, support the validity and utility of the equivalence principle between exothermic reacting turbulent shear flows and a corresponding equivalent non-reacting flow under otherwise identical conditions.