For each pair of gases, select the one that most likely has the highest rate of effusion. Use the periodic table if necessary.
Oxygen (02) or hydrogen (H2):

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.