Will someone please help me my brain is fried?

To find the enthalpy of a reaction in the lab, you measured the of the reactants and the change during the reaction.

What is a substance? a. a physical property of matter b. a chemical property of matter c. an element or compound that cannot be physically separated d. characteristics used to tell the difference between mixtures

The empirical formula of a compound is ch2o and its mass is 120 amu/molecule, what is its formula?