Bond enthalpies of \( H_2 \), \( X_2 \), and \( HX \) are in the ratio 2:1:2. If enthalpy of formation of \( HX \) is -50 kJ/mol\(^{-1}\), the bond enthalpy of \( X_2 \) is:
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Bond enthalpies can be used to calculate enthalpy changes based on the ratio of bond strengths in the molecules involved.