[填空题]
Consider the following re2cgci; 5: 6ug*uz xaoiaction:nba.m;7nmw63 8o, ffxni;ao y $C_2H_4$(g)+$H_2$(g)→$C_2H_6$(g)
ΔH is -136kJ mol$^{-1}$
ΔS is -121jk$^{-1}$ mol$^{-1}$
ΔG at 298K is -99.9kJ mol$^{-1}$
1.1.Explain why the enthalpy of formation of $H_2$ is 0 kJ mol$^{-1}$.
1.2.Explain why the entropy change for this reaction is negative.
2.Explain how a reaction can be spontaneous with a negative entropy change.
3.Calculate the temperature at which this reaction is no longer spontaneous.
T= K
