Advices For Studying Organic Chemistry

CH 3 • + Cl–Cl CH 3 –Cl + •Cl ∆H° = – 106 kJ mol–1
CH 3 –H + Cl–Cl CH 3 –Cl + H–Cl ∆H° = – 102 kJ mol–1

1) The addition of the values of ∆H° for the chain-propagating steps yields the

overall value of ∆H° for the reaction.

10.5A THE OVERALL FREE-ENERGY CHANGE:

1. For many reactions the entropy change is so small that the term T∆S° is almost
   zero, and ∆G° is approximately equal to ∆H° in ∆G° = ∆H° – T∆S°.


2. Degrees of freedom are associated with ways in which monement or changes in
   relative position can occur for a molecule and its constituent atoms.

Figure 10.2 Translational, rotational, and vibrational degrees of freedom for a
simple diatomic molecule.

3. The reaction of methane with chlorine:
   CH 4 + Cl 2 CH 3 Cl + HCl

1) 2 moles of the products are formed from 2 moles of the reactants ⇒ the number

of translational degrees of freedom available to products and reactants are the

same.

2) CH 3 Cl is a tetrahedral molecule like CH 4 , and HCl us a diatomic molecule like

Cl 2 ⇒ the number of vibrational and rotational degrees of freedom available

to products and reactants are approximately the same.

3) The entropy change for this reaction is quite small, ∆S° = + 2.8 J K–1 mol–1 ⇒ at