posted by Bliss .
use the following data to calculate the mean bond enthalpy values for the C-H and C-C bonds.
CH4(g)-C(g) + 4H(g) standard enthalpy change is +1648 kj/mol
C2H6(g)-2C(g) + 6H(g) standard enthalpy change is +2820 kj/mol
412 kj mol^-1 (4 bonds and they're all C-H so it's 1648 /4)
and 2820-(6*412) = 348 kj mol^-1
remember there aren't 2 C-C bonds - just the one!!!