Chapter 2: Kinetic Particle Theory Classification of Matter 1. Matter takes up space and has mass. 2. Matter can exist in three different physical states; i.e. solid, liquid and gas. 3. The kinetic particle theory states the following: a. Matter is made up of tiny particles. These tiny particles can be atoms, molecules or ions. b. The particles have kinetic energy and hence, are in constant and random motion. c. The particulate model of matter is used to explain the properties and characteristics of matter in different physical states.
Solid
Vibrate at fixed positions only
Motion Attractive force Arrangement Distance
Physical state
Very strong Regular pattern and fixed positions Very closely packed together
Properties
Solids Not compressible No able to flow
Fixed volume but no fixed shape
Liquids
Takes the shape of container Able to flow easily Not compressible
Gas
Move about within confined space and slide past each other Moderate
Move freely in all directions at high speed Very weak
Irregular and random
Irregular and random
Quite close together
Very far apart
Explanation in terms of the particulate model of matter
Fixed volume and shape
Liquid
Particles are arranged in a fixed position and a regular pattern. The strong attractive force prevents the particles from breaking away from their fixed positions. The particles are closely packed together, so there is little spaces for compression to occur. The particles can only vibrate at their fixed positions. The moderately strong attractive force prevents the particles from escaping from their positions. However, the particles can move about and slide past each other freely. The particles are able to move about and slide past each other. The particles are arranged quite closely together, so there are less spaces between them.
No fixed volume and shape
Gases
Flow easily Takes the shape of the container Compressible
The particles can move freely and randomly in all the available spaces. The attractive forces of attraction between the particles are negligible. The particles move freely at high speeds. The particles are far apart from each other, so they exists empty space for compression.
Energy changes during Interconversion of P hysical States
A change in the physical state does not produce new substances. It is called a physical change. When a substance undergoes changes in physical states, energy is either given out to the surroundings or taken in from the surroundings. When energy is given out to the surroundings, it is called exothermic. When energy is taken in from the surroundings, it is known as endothermic. A pure substance has a fixed boiling and melting point. Changes in the physical states of a substance takes place at these two partic ular temperatures. Energy is involved in the breaking down of the attractive forces or the formation of attractive forces between particles during changes in physical states of a substance. Label endothermic and exothermic for the following physical changes in the diagram below:
Process Melting Boiling
Definition
Sublimation Freezing Condensation
Deposition
A process where solid changes into a liquid. A process where liquid changes into gas. Process where solid changes into gas directly without becoming a liquid. Process where gas changes into liquid. Process where liquid changes into solid Process where a gas changes into solid without becoming a liquid.
Energy changes
Reason for energy change
Endothermic
To overcome the attractive forces of attraction between the particles
Exothermic
To allow the formation of attractive forces between the particles
NOTE: Evaporation is a process in which a liquid changes into a gas. This process is endothermic. However, evaporation is different from boiling because it takes place below the boiling point of the substance.
Questions 1. Which of the following descriptions about the particles in a dilute ethanol solution at room temperature is correct?
A B C D
Ethanol molecules Close together, vibrate at fixed positions Widely separated, vibrate at fixed positions Close together, vibrate at fixed positions Widely separated, moving at random
Water Close together, vibrate at fixed positions Widely separated, moving at random Widely separated, not moving Close together, moving at random
2. The melting points and boiling points of some metals are given below. Which metal remains as a liquid over the shortest range of temperature?
A B C D
Metal Al Cu Fe Pt
Melting point /°C 660 1083 2535 1769
Boiling point /°C 2470 2595 3000 4530
3. The diagram shows the spacing of molecules in a substance at atmospheric pressure but at two different temperatures. at -175°C
at -85°C
What could be the melting point and boiling point of the substance?
A B C D
Melting point /°C -180 -170 -180 -170
Boiling point /°C -80 -90 -90 -80
4. Which statement about the behaviour of the particles in a liquid is correct? a. They spread throughout the container in which they are contained. b. They are able to move at high speeds. c. They are arranged in irregular patterns. d. There are large spaces between the particles.
5. The boiling points of some elements are given below.
Element Nitrogen Xenon Oxygen
Boiling point /°C -196 -108 -183
These three gases are made into liquid air at -200°C and are separated by fractional distillation. When the temperature is increased by 50°C, which substance(s) would remain in liquid state? a. b. c. d.
Nitrogen Xenon Oxygen Nitrogen and oxygen
6. Iodine has a melting point of 114°C and a boiling point of 184°C. At which temperature is iodine a liquid? a. 80°C b. 100°C c. 160°C d. 200°C 7. Which of the following processes is energy given out to the surroundings? a. Melting b. Sublimation c. Evaporation d. Condensation 8. The melting points and boiling poi nts of seven substances A to G are given in the following table.
Substance A B C D E F G
Melting point /°C -82 -25 -15 44 110 85 1250
a. Which substance is a gas at room temperature?
b. Which substance is a solid at 1000°C?
Boiling point /°C 400 -50 60 280 185 450 2150
c.
Which substance changes its physical state when the temperature changes from 0°C to 50°C?
d. Which substance exists as a liquid over the largest range of temperature?
e. Sketch the arrangement of particles of substance F at room temperature.
9. A fractional distillation is used to separate a mixture of ethanol (boiling point: 78°C) and water. a. Explain why the bulb of the thermometer must be placed near the outlet of the condenser connecting to the fractionating column.
b. The boiling of the mixture is bumpy. Suggest one way to reduce this boiling effect.
c.
Which of the compounds is distilled first? Explain your answer.
d. Sketch a graph of temperature-time for the distillation of both substances from room temperature to the boiling point of water.
10. Which statement about the molecules in carbon dioxide gas is correct? a. b. c. d.
The molecules are close together. The molecules are diatomic. The molecules are in fixed positions. The molecules move randomly.
11. An endothermic reaction is one in which a. b. c. d.
The products contain more energy than the reactants. The reaction container becomes hot. Light is given out. Sound is produced.
12. The diagrams shows the particles in three substances, Q , R and S.
Which of the structures in the above diagrams best represents a. Solid copper: b. Brass:
13. A mixture of carbon monoxide and hydrogen gas is prepared by passing steam over heated carbon. Energy is absorbed. a.
Construct a balanced equation with state symbols for this reaction.
b. In this reaction, the covalent bonds in water molecules are broken. Is the bond breaking process exothermic or endothermic?
14. Which statement about the molecules in carbon dioxide gas is not correct? a. b. c. d.
The molecules are triatomic. The molecules move randomly. The molecules are close together. The molecules spread throughout their container.
15. Which changes occur when a solid at 20°C becomes a liquid at 78 °C?
Separation of particles Decreases Decreases Increases Increases
A B C D
Energy of particles Increases Decreases Increases Decreases
Attractive forces between particles Decreases Increases Decreases Increases
16. Which of the following is a mixture? a. b. c. d.
Crude oil Glucose Steam Salt
17. Which of the following atoms/molecules have the least kinetic energy at room temperature and pressure? a. b. c. d.
Mercury Water Potassium Ammonia
18. Neon exists as a gas at room temperature and pressure because __________. a. b. c. d.
The attractive forces between neon atoms are weak. Neon molecules are diatomic. Neon is chemically inert. The valence electron shell of an atom has octet structure.
19. In a vessel containing ice, water and water vapour, which of the following statements is correct? a. b. c. d.
The molecules in water vapour have the mo st energy. Energy is released when water changes from solid to liquid. The volume of water in all three states is the same. Ice has weaker forces of attraction between its molecules compared to water.
20. For a given substance, does the density of increases or decreases when the substance sublimes?
