# Enthalpy of NaOH(s) -> NaOH(g)

1. Mar 7, 2013

### ghostanime2001

Enthalpy of NaOH(s) --> NaOH(g)

1. The problem statement, all variables and given/known data

Given:
1. $Na_{(s)} \rightarrow Na_{(g)}$ $\Delta H = 109 kJ$

2. $\Delta H^{\circ}_{diss} = 251\:kJ\:for\:O_{2}$

3. $\Delta H^{\circ}_{diss} = 435\:kJ\:for\_{2}$

4. $\Delta H^{\circ}_{diss} = 465\:kJ\:for\:O-H$

5. $\Delta H^{\circ}_{diss} = 255\:kJ\:for\:Na-O$

6. $\Delta H_{soln} = -46\:kJ\:for\:NaOH_{(s)}$

7. $\Delta H^{\circ}_{f} = -427\:kJ\:for\:NaOH_{(s)}$

Predict $\Delta H$ for $NaOH_{(s)} \rightarrow NaOH_{(g)}$ ???

2. Relevant equations
see above

3. The attempt at a solution
I understand the standard states of all substances for #1-3 but I am unsure of #4,5,7. I don't understand what the standard states are for #4,5 (both reactants and products). I don't understand what the physical state of sodium is for #7 (is it solid or gas ?). Also how will the aqueous ions produced from dissociation of sodium hydroxide in #6 cancel out ? and how will covalent bonds of $Na-O$ or $O-H$ as reactants cancel out ?

Thanks!! :)

2. Mar 8, 2013

### Staff: Mentor

You can assume bond dissociation enthalpy doesn't depend on the state. In #7 you start with elements in the standard state and end with NaOH in the standard state.

3. Mar 8, 2013

### ghostanime2001

How will I cancel aqueous hydroxide ion or sodium cation ? So the standard state of elemental sodium in #7 is solid ? Also, after O--H bond or Na--O bond dissociates do the Na or O or H assume a gaseous state ?

4. Mar 29, 2013

### ghostanime2001

Any new thoughts from my previous reply ?