States and Phases of Matter

Chemistry, HSSC-Punjab First Year. This chapter is split into 32 topics and has 768 practice questions. The topics covered are listed below, followed by 10 free sample questions from the chapter.

Topics in this chapter

1. Evaporation and cooling 23 questions
2. Boiling points of common liquids 24 questions
3. Structure of ice and heat capacity of water 22 questions
4. Temperature and pressure units for gas calculations 23 questions
5. Boiling points of halogens and noble gases 27 questions
6. Ideal gas equation: moles and mass of a gas 24 questions
7. Permanent dipole-permanent dipole forces 22 questions
8. Boiling point and external pressure 20 questions
9. Density of gases from the ideal gas equation 28 questions
10. Hydrogen bonding 27 questions
11. Amorphous solids and comparison with crystalline solids 24 questions
12. London dispersion forces 23 questions
13. Ideal gas equation: pressure 25 questions
14. Vapour pressure and dynamic equilibrium 23 questions
15. Properties of gases 24 questions
16. Ideal gas equation: volume 25 questions
17. Energetics of phase changes 28 questions
18. Gas laws and the ideal gas equation 24 questions
19. Comparison of solids, liquids and gases 24 questions
20. Liquid crystals: nature and properties 26 questions
21. Properties of crystalline solids 26 questions
22. Relative molecular mass from the ideal gas equation 26 questions
23. Exercise items on intermolecular forces and states 25 questions
24. Types of intermolecular forces 22 questions
25. Properties of liquids and kinetic molecular theory 23 questions
26. Volume units, SI units and the gas constant 21 questions
27. Surface area, chain length and boiling point 20 questions
28. Ideal gas equation: temperature 24 questions
29. Group 16 hydrides, heat of vaporisation and boiling points 23 questions
30. Surface tension of liquids 25 questions
31. Viscosity of liquids 23 questions
32. General properties of solids 24 questions

Sample questions: States and Phases of Matter

10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.

Q1. In a laboratory experiment, 150 cm³ of a volatile liquid was completely vaporised at 98 °C and a pressure of 1.01 × 10⁵ Pa. The mass of the vapour was found to be 0.495 g. Determine the molecular mass of the liquid. (R = 8.314 J K⁻¹ mol⁻¹)

• A. 101 g mol⁻¹(correct answer)
• B. 26.6 g mol⁻¹
• C. 101000 g mol⁻¹
• D. 0.101 g mol⁻¹

Answer: A.V = 150 cm³ = 1.50 × 10⁻⁴ m³; T = 98 + 273 = 371 K; M = mRT/(PV) = 0.495 × 8.314 × 371 / (1.01 × 10⁵ × 1.50 × 10⁻⁴) = 101 g mol⁻¹.

Q2. Compared with diffusion in gases, the rate of diffusion in liquids is:

• A. much lower, because liquid molecules are closer and more strongly attracted(correct answer)
• B. the same, because both are fluids with random molecular motion in them
• C. zero, because liquid molecules cannot move past each other at all
• D. much higher, because liquid molecules are lighter and move faster than gas ones

Answer: A.The book states that liquids also diffuse, but the rate is much lower than in gases because of stronger intermolecular forces and little free space.

Q3. Liquids are about how many times less compressible than gases?

• A. 10⁵ times(correct answer)
• B. 10⁹ times
• C. 10² times
• D. 10 times

Answer: A.The book states that liquids are 10⁵ times less compressible than gases but about 10 times more compressible than solids.

Q4. Which of the following represents increasing kinetic energy of molecules at the same temperature?

• A. none of them, as the average kinetic energy depends on temperature only(correct answer)
• B. gas < liquid < solid, with the molecules of solids the most energetic
• C. solid < liquid < gas, with the molecules of gases the most energetic
• D. liquid < gas < solid, with the molecules of solids the most energetic

Answer: A.At the same temperature the average kinetic energy of molecules is the same in all states (standard knowledge); the states differ in the intermolecular forces.

Q5. Quick Check 5.2a: In petrol refining, straight-chain hydrocarbons are converted to branched-chain ones. A possible reason (in terms of forces) is that branched molecules:

• A. have weaker London forces, so they are more volatile(correct answer)
• B. form hydrogen bonds, so the fuel becomes denser
• C. have a higher boiling point than straight-chain ones
• D. have stronger London forces, so they are less volatile

Answer: A.Branching reduces surface area and intermolecular attraction; the improved volatility of the fuel is one possible reason.

Q6. Exercise IV: Which is the correct order of ΔHᵥ values (from greatest to least) for H₂O, NH₃ and F₂?

• A. NH₃ > H₂O > F₂
• B. F₂ > NH₃ > H₂O
• C. H₂O > NH₃ > F₂(correct answer)
• D. H₂O > F₂ > NH₃

Answer: C.Water has the strongest hydrogen bonding, NH₃ weaker hydrogen bonding, F₂ only London forces. The book's exercise wording says 'increasing' but lists this order, a book inconsistency.

Q7. A pressure cooker cooks food faster because:

• A. the vapour escapes quickly and removes heat from the food, so it cooks faster
• B. the water inside the cooker never boils and so the food cooks in dry heat
• C. the increased pressure lowers the boiling point, so the food is heated to a lower temperature
• D. the increased pressure raises the boiling point, so the food is heated to a higher temperature(correct answer)

Answer: D.Quick Check 5.6b: the closed container does not allow vapour to escape, the pressure rises and the boiling temperature increases.

Q8. Which of the following requires the larger amount of heat per mole at the same temperature?

• A. compressing a gas
• B. cooling of the same liquid by 1 °C
• C. vaporisation of a liquid(correct answer)
• D. fusion of the same substance

Answer: C.The heat of vaporisation is generally much greater than the heat of fusion because the molecules must be separated completely.

Q9. Quick Check 5.8c: The property of liquid crystals that makes them useful in temperature-sensing devices is that:

• A. their density does not change when they are heated
• B. their optical properties (colour) change with temperature(correct answer)
• C. they do not respond to heat that is applied to them
• D. they are always cloudy at every temperature

Answer: B.Cholesteric liquid crystals change colour with temperature and so are used in sensors (standard explanation of the property).

Q10. How do liquid crystals resemble liquids and solids? Choose the statement that correctly lists the resemblance to both.

• A. gaseous behaviour like liquids and high density like solids
• B. isotropy like liquids and a sharp melting point like solids
• C. flow like solids and rigidity like liquids, in all conditions
• D. flow and viscosity like liquids; optical properties like crystals(correct answer)

Answer: D.Descriptive Question 6: resemblance to liquids (flow, viscosity) and to solids (optical properties, somewhat rigid, ordered).