Why does the inner side of a window pane in a room sweat in cold weather?

The reaction, Cr_2O_3 + 2Al rarr Al_2O_3 + 2Cr (DeltaG^@ = -421KJ) is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?

Why does our palm feel cold when we put some acetone or petrol or perfume on it?