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CAIE A-Level Chemistry 4.1 Ideal and Real Gases

Practise ideal-gas calculations and explaining why real gases deviate when particle volume or intermolecular attraction matters.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • use pV=nRT with pressure in Pa, volume in m3, temperature in K and R in matching units
  • rearrange before substitution and convert cm3 or dm3, kPa and °C correctly
  • explain high-pressure, low-temperature deviation through particle volume and intermolecular attraction

Covered syllabus points

4.1.1—Origin of pressure in a gas4.1.2—Ideal gases have zero particle volume and no4.1.3—Ideal gas equation pV = nRT

4.1 Gases: ideal, real and pV = nRT question 1

[Maximum number: 4]

The strength of interaction between particles determines whether the substance is a solid, liquid or gas at room temperature.

Question (a)

(a)

Nitrogen, N2\mathrm{N}_{2}, is also a gas at room temperature and pressure. Neither CO nor N2\mathrm{N}_{2} is an ideal gas.

[ 4 ]

Question (i)

(i)

State two assumptions that are made about the behaviour of particles in an ideal gas.

1
2

[ 2 ]

Question (ii)

(ii)

Explain why N2\mathrm{N}_{2} does not behave as an ideal gas at very high pressures.

[ 2 ]

4.1 Gases: ideal, real and pV = nRT question 2

[Maximum number: 3]

The Pauling electronegativity values of elements can be used to predict the chemical properties of compounds.

Use the information in Table 1.1 to answer the following questions.

Table 1.1

Table 1.1

At 150∘C150^{\circ} \mathrm{C} and 103 kPa , all of the compounds listed in Table 1.2 are gases.

Under these conditions, 0.284 g of one of the compounds occupies a volume of 127 cm3127 \mathrm{~cm}^{3}.
Use this information to calculate the MrM_{\mathrm{r}} of the compound. Hence, identify the compound from those given in Table 1.2.

Show your working.
Mr=M_{\mathrm{r}}= identity of compound =

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