## Finding Vapor Pressure of Liquid (HW #10.109)

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Glenda Marshall DIS 3M
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### Finding Vapor Pressure of Liquid (HW #10.109)

What does it mean to find vapor pressure of a liquid? In problem #10.109 in the homework, part (b) asks "what is the vapor pressure of liquid bromine?" and it does not provide an equation or any other information. It the solutions manual, they solved for K and used that value as the vapor pressure. I don't understand why this is possible. Also part c asks "what is the partial pressure of Br2(g) above the liquid in a bottle of bromine at 25 degrees celsius?" I don't know how this is any different from part (b). Any help would be appreciated! Thanks!

Chem_Mod
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### Re: Finding Vapor Pressure of Liquid (HW #10.109)

The vapor pressure is the pressure of a gas that is in equilibrium with its liquid. So if we write the equilibrium expression for Br2 (l) --> Br2 (g), it is just K = [Br2 (g)] because liquids and solids are not included in equilibrium expressions. Therefore, K is exactly the vapor pressure that is asked for.

For part c), the problem wants the partial pressure of monatomic bromine. So you'll use the answer to part a) and solve for [Br (g)] after taking the square root of [Br (g)]^2

Justin Le 2I
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Joined: Fri Sep 26, 2014 2:02 pm

### Re: Finding Vapor Pressure of Liquid (HW #10.109)

The solutions manual makes this a little confusing because it says PBr(g)^2 but it should actually be without the exponent because we are just solving for the pressure of Br(g)