1. Dec 3, 2004

### glycogen

Given: Cl2 = 58 kcal/mole ------> 2cl

1. 58 kcal/mole is the bond dissociation energy T F

2. 58 kcal/mole is an entropy term T F

3. this reactin is endothermic T F

I dont understand get it! Any help woud be appreciated.

2. Dec 3, 2004

### Staff: Mentor

Did you mean to write $$Cl_2$$+58 kcal/mole $$\rightarrow$$ 2 Cl?

If so, then think about what it means. What is happening when $$Cl_2 \rightarrow$$ 2 Cl?

What are you doing with the energy?

Can it be the 'entropy' term?

3. Dec 3, 2004

### so-crates

Thats one notation. Most textbooks nowadays would say

$$Cl_2 \longrightarrow 2 Cl \ \ \ \ \Delta H^0 = +58 \ \ kcal/mol$$

to avoid confusion about the "energy" change in the system. (At constant pressure, enthalpy = heat added or lost)

A positive enthalphy change corresponds with heat being absorbed by the system. A negative enthalpy change corresponds to heat being released by the system.

4. Dec 4, 2004

### glycogen

Thanks for the explanations :). The formula makes sense now!