Stored energy in molecule is transformed into mechanical energy and dissipated as waste heat?

Question

say 20% of energy stored in chem. bonds of molecules is transformed into mechanical energy. the other 80% is waste heat. why??

A. 1st law of thermodynamics

B. 2nd law of thermodynamics

C. when energy is converted from one form to another, some of the energy is converted into heat.

D. both A and B

E. Both B and C

Answer 1

Correct answer is E.

Say, you burn fuel in an engine. It is converted into mechanical energy and in heated exhaust gases.

The second law of thermodynamics says  you cannot use it 100%.

.

Answer 2

Sort of a strange question.  I am trying to think of any case were chemical energy goes straight into mechanical energy.  In a gas engine, ALL of the chemical energy is converted to heat.  Then some of this heat energy is converted to mechanical energy and the rest is waste heat.

Sorry, but I don't know the answer.