{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Horvath Practice Problems 91

# Horvath Practice Problems 91 - 4 H ’s for the component...

This preview shows page 1. Sign up to view the full content.

Hess’ Law Both total energy, E, and enthalpy, H , are what are called state functions A state function is a function that depends only on the partic- ular state that the system is in. It is completely independent of how the system arrived at that state. For example consider heating in water from 300 K to 310 K. You would calculate the same 4 H or 4 E regardless as to whether you heated directly from 300 K to 310 K or if you fi rst cooled to 290 K then heated to 360 K and then cooled to 310 K. An important consequence of enthalpy being a state function is Hess’ law which states that if a reaction is the sum of two or more reactions, 4 H for the overall reaction is the sum of the
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 4 H ’s for the component reactions. That is 4 H is solely determined by 4 H = H products − H reactants (21.6) regardless of how the reactants became the products. For example, 4 H for the reaction 2 C 6 H 6 + 15 O 2 → 12 CO 2 + 6 H 2 O ( 2 1 . 7 ) is the same as the sum of the 4 H ’s for the following reactions 2 C 6 H 6 → 12 C + 6 H 2 (21.8) 12 C + 6 H 2 + 15 O 2 → 12 CO 2 + 6 H 2 O ( 2 1 . 9 ) Hess’s law is very handy because it would be impossible to measure enthalpy changes for every imaginable reaction were it not for Hess’ law. 90 REVIEW OF THE FIRST LAW, ENTHALPY, AND HESS’ LAW...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online