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Wize High School Grade 11 Chemistry Textbook > Gas Laws

Ideal Gases

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Ideal Gases and the Ideal Gas Law

Ideal Gas Law

  • Combining Boyle's Law, Charles' Law and Avogadro's Law gives us the ideal gas law
PV=nRT\boxed{PV=nRT}
P is pressure measured in kPa
V is volume measured in L
n is number of moles of the gas in mol
R is the ideal gas constant with a value of 8.314 L kPa mol-1 K-1
T is temperature measured in K
  • There are other values of R involving other units, such as 0.08206 L atm mol-1 K-1
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Ideal Gases Assumptions

  • Ideal gas particles are in constant, random, straight motion
  • Ideal gas particles occupy a negligible portion of the total volume of the container - their individual contribution may be ignored

  • Ideal gas particles collide elastically with themselves and the walls of the container; there is no loss of kinetic energy
  • Ideal gas particles do not attract, nor repel each other


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Deviations from Ideal Gas Behavior

  • In reality, no gas behaves ideally.
  • Gases behave most ideally at:
  • High temperatures: collisions between particles are elastic
  • Low pressures: particle size is negligible compared to the space between particles
  • Ideal gas behavior breaks at:
  • Low temperatures: low molecular speed, collisions are no longer elastic
  • High pressures: volume of the individual gas particles no longer negligible


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Example: Using the Ideal Gas Law

1.1moles of Argon are stored in a 2.0L container kept at 10°C. What is the pressure of this gas in kPa?

Gather your data:
n=1.1moles
V=2.0L
T=10°C +273.15 = 283.15K
P=?
We can use the ideal gas law.
PV=nRTPV=nRT
Isolate for pressure:
P=nRTVP= \dfrac{nRT}{V}
P=1.1mol×283.15K×8.314L⋅kPamol⋅K2.0LP=\dfrac{1.1mol\times283.15K\times8.314 \frac{L\cdot kPa}{mol\cdot K}}{2.0L}
P=1295kPa=1.3×103kPaP=1295kPa=1.3\times10^3 kPa

Practice: Ideal vs Real Gases

Real gas behaviour deviates from ideal gas behaviour because real gas particles have:
Answer the following two questions based on the Ideal Gas Law:
What is the volume of 2.5mol of Ne at 298K and 101.325kPa?

Enter your answer to one decimal point and make sure to include units.

Practice: Using the Ideal Gas Law

A 0.483g sample of gas occupies a volume of 0.530 L at 130°C and 109kPa. What is the molar mass of this gas? Give your answer rounded to one decimal point; do not include units.