For example, the conversion of glucose to glucose-6-phosphate by the enzyme hexokinase is thermodynamically unfavourable, with #ΔG = "+14.3 kJ/mol"#.
The hydrolysis of #"ATP"# to #"ADP"# is a highly favourable process, with #ΔG = "-30.5 kJ/mol"#.
The reactions are
#"glucose " + cancel("P"_i) → "glucose-6-P" + cancel("H"_2"O")#; #ΔG = "+14.3 kJ/mol"#
#"ATP" + cancel("H"_2"O") → "ADP" + cancel("P"_i)#; #ΔG = "-30.5 kJ/mol"#
#bar("glucose " + "ATP" stackrel("hexokinase")(→) "glucose-6-P" + "ADP")#; #ΔG = "-16.2 kJ/mol"#
The coupled reaction has a negative free energy, so the process is thermodynamically favourable.