Identify each enthalpy change by name and classify each change as exothermic or endothermic.
a)1 mol C3H8 (l) ==> 1 mol C3H8 (g)
b)1 mol Hg (l) ==> 1 mol Hg (s)
c)1 mol NH3 (g) ==> 1 mol NH3 (l)
d)1 mol NaCl(s) + 3.88kJ/mol ==> 1 mol NaCl (aq)
e)1 mol NaCL (s) ==> 1 mol NaCl (l)
To identify and classify each enthalpy change, we need to determine whether the reaction is exothermic or endothermic.
a) 1 mol C3H8 (l) → 1 mol C3H8 (g)
This change involves the phase transition from liquid to gas. Since this transition typically requires energy, it is endothermic.
b) 1 mol Hg (l) → 1 mol Hg (s)
This change involves the phase transition from liquid to solid. When a substance changes from a more disordered state (liquid) to a more ordered state (solid), energy is typically released. Therefore, this change is exothermic.
c) 1 mol NH3 (g) → 1 mol NH3 (l)
This change involves the phase transition from gas to liquid. As mentioned earlier, this transition usually requires energy, so it is endothermic.
d) 1 mol NaCl(s) + 3.88 kJ/mol → 1 mol NaCl(aq)
The given enthalpy change of 3.88 kJ/mol indicates that energy is being added to the system. The reactants are in a solid state, and the product is an aqueous solution. Dissolving a solid in water typically absorbs energy, so this change is endothermic.
e) 1 mol NaCl(s) → 1 mol NaCl(l)
This change involves the phase transition from solid to liquid. Again, when a substance changes from a more ordered state (solid) to a less ordered state (liquid), energy is usually required. Thus, this change is endothermic.