If endothermic reactions absorb heat from the surroundings, how can they be spontaneous, if heat only flows from high temp to low temp objects?
A spontaneous endothermic reaction can occur when the changes in enthalpy and entropy yield a negative Gibbs free energy. An endothermic reaction can be spontaneous if entropy increases by more than the change in enthalpy.
$\Delta G = \Delta H - T\Delta S$
For endothermic r̥eactions, $\Delta H$> 0 and thus if the value of $-T\Delta S$ overshadows the $\Delta H$ value (usually at very high temperatures) then the overall value of $\Delta G$ becomes negative and thus the reaction becomes spontaneous.