Am I doing this vapour pressure problem correctly?

In summary, the given problem involves the vapour pressure of ethanol at a specific temperature and the amount of liquid ethanol remaining after it reaches equilibrium with its vapour in a closed container. Using the ideal gas equation and the given values, it is determined that only a portion of the ethanol is converted into vapour, resulting in 0.797 grams of liquid ethanol remaining.
  • #1
Eclair_de_XII
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Homework Statement


'The vapour pressure of ethanol (C2H5OH) at 19°C is 40.0 torr. A 1.00-g sample of ethanol is placed in a 2.00 L container at 19°C. If the container is closed and the ethanol is allowed to reach equilibrium with its vapour, how many grams of liquid ethanol remain?'

Homework Equations


PV = nRT
R = 62.36 L⋅torr / mol⋅K

The Attempt at a Solution


Basically, when I tried to plug in all the numbers into the ideal gas equation (with the given mol number of 1/46), it wasn't quite equal. Then I figured, that not all the ethanol is converted into vapour; only some of it. And this equation really only applies to gases (a.k.a. vapours). I didn't know how much, so that's basically what I set out to find out with what I was given.

(40.0 torr)(2.00 L) = (x mol)(62.36 L⋅torr/1 mol⋅K)(292 K)
80 L⋅torr = x19209.12 L⋅torr
x = 0.0044 mol C2H5OH (g)
0.0044 mol(46.06844 g/1 mol) = 0.203 g C2H5OH (g)
1.00 - 0.203 = 0.797 g C2H5OH (l)
 
Last edited:
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  • #2
Looks OK to me.
 
  • #3
Thank you.
 

1. What is vapour pressure?

Vapour pressure is the pressure exerted by a gas in equilibrium with its liquid or solid form at a given temperature. It is a measure of the tendency of a substance to escape from its liquid or solid phase and enter the gas phase.

2. How do I calculate vapour pressure?

Vapour pressure can be calculated using the Clausius-Clapeyron equation, which relates the vapour pressure of a substance to its temperature and enthalpy of vaporization. It is important to use the correct units and constants for accurate calculations.

3. What factors affect vapour pressure?

The main factors that affect vapour pressure are temperature and intermolecular forces. As temperature increases, the vapour pressure also increases, while stronger intermolecular forces lead to lower vapour pressure.

4. Why is vapour pressure important?

Vapour pressure is important in many industrial and scientific applications, such as in the production of pharmaceuticals and the design of refrigeration systems. It also plays a crucial role in the Earth's water cycle and the evaporation of liquids.

5. How do I know if I am calculating vapour pressure correctly?

To ensure accuracy in your calculations, it is important to double-check your equations, units, and constants. Additionally, comparing your results with those obtained from reliable sources or with experimental data can help verify the correctness of your calculation.

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