Question

What are the steps to solve this problem? "The enthalpies of combustion of glucose and ethanol are -2813kj/mol and -1369kj/mol, use Hess's law to calculate the enthalpy change when 0.500 kg of glucose is allowed to ferment." Please help.

Answer 1

Write and balance the combustion equation for ethanol + O2 ==> CO2 + H2O as eqn 1. Then reverse that equation multiply it by an integer to make mols CO2 cancel with mols CO2 in the next equation you write (also, change the sign for delta H and multiply by the same factor you use above).

The second equation is the combustion equation for glucose +O2 ==> CO2 + H2O. Balance that.
Then add the reverse and multiplied equation 1 to equation 2. Add the delta H values to find the overall dH for the new reaction.