Van der Waals Equation

The Van der Waals Equation is used when dealing with real, non-ideal gases. 

Understanding the Van der Waals Equation

Concept: Van der Waals Equation

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The Van der Waals Equation takes into consideration that real gases do not behave ideally. As a result these gases can experience attractive or repulsive forces while also having definite volumes. 

Calculations with the Van der Waals Equation

Example: Van der Waals Equation

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Example: Van der Waals Equation

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Example: Van der Waals Equation

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Example: Van der Waals Equation

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Van der Waals Equation Additional Practice Problems

Use the van der Waals equation of state to calculate the pressure of 2.50 mol of H2O at 497 K in a 4.90 L vessel. Van der Waals constants can be found here. 

Use the ideal gas equation to calculate the pressure under the same conditions.

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Calculate the pressure in bar of 8.5 mol of ethanol vapor in a 12.0-L container held at 82°C:

a. treating ethanol vapor as a van der Waal's gas,

b. treating ethanol as an ideal gas. 

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Use the van der Waals equation of state to calculate the pressure of 2.20 mol of Xe at 497 K in a 4.40 L vessel. Van der Waals constants can be found here. 

Use the ideal gas equation to calculate the pressure under the same conditions. 

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Use the van der Waals equation of state to calculate the pressure of 2.80 mol of NH3 at 483 K in a 5.50 L vessel.

Use the ideal gas equation to calculate the pressure under the same conditions. 

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At high pressures, real gases do not behave ideally. (a) Use the van der Waals equation and data in the text to calculate the pressure exerted by 21.0 g H2 at 20°C in a 1.00 L container. (b) Repeat the calculation assuming that the gas behaves like an ideal gas. 

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Use the van der Waals equation to calculate the pressure exerted by 1.330 mol of Cl_2 in a volume of 5.285 L at a temperature of 303.0 K.

 Use the ideal gas equation to calculate the pressure exerted by 1.330 mol of Cl_2 in a volume of 5.285 L at a temperature of 303.0 K.

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Calculate the pressure that CCl4 will exert at 43 C if 1.20 mol occupies 33.5 L, assuming that CCl4 obeys the ideal-gas equation: P = CCl4 obeys the van der Waals equation. (Values for the van der Waals constants are a = 20.4, b = 0.1383.)


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Use the van der Waals equation of state to calculate the pressure of 2.70 mol of Xe at 473 K in a 5.50-L vessel. Van der Waals constants can be found below.

P= ______________ atm

Use the ideal gas equation to calculate the pressure under the same conditions.

P=_______________atm

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Which gas molecule do you expect to be the largest? (a and b are Van der Waals constants.)

1. Butane

2. Acetonitrile

3. Freon

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Use the van der Waals equation and the ideal gas equation to calculate the pressure exerted by 1.000 mol of Cl2 in a volume of 5.000 L. at a temperature of 273.0 K. Explain why the two values are different. 

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Use the van der Waal's equation to calculate the pressure (in atm) exerted by 1.00 mol of chlorine gas confined to a volume of 2.00 L at 273K. The value of a = 6.49 L2 atm mol-2, and that of b = 0.0562 L mol-1 for chlorine gas.

a) no given answer is close

b) 9.9

c) 4.12

d) 1.54

e) 3.73

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The constant a in the Van der Waal’s equation corrects for ________and is important at ________.

a. intermolecular attraction, high temperature

b. intermolecular attraction, low temperature

c. lower than average energy of molecules, low temperature

d. volume of molecules, low pressure

e. volume of molecules, high pressure

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Which gas would you expect to have the largest value for the van der Waals constant “a”?

1. Ne

2. CH4

3. He

4. NH3

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