i. CO2(g)+ H2(g) CO(g)+H2O(g) ΔH1=+41 kJ·mol-1 ,
ii. 2CO2(g)+6 H2(g) CH3OCH3(g)+3H2O(g) ΔH2=-121 kJ·mol-1 ,
iii. 2CH3OH(g) CH3OCH3(g)+H2O(g) ΔH3=-23kJ·mol-1 ,
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