Chapter 5 States of Matter

Question 1

Gas Pressure

Answer 1

Gases in a container exert a pressure as the gas molecule are constantly colliding with the wall of the container

Question 2

Changing gas volume

Answer 2

• Decreasing the volume (at constant temperature) of the container causes the molecules to be squashed together which results in more frequent collisions with the container wall
• The pressure of the gas increases
• The volume is therefore inversely proportional to the pressure (at constant temperature)
• —-A graph of volume of gas plotted against 1/pressure gives a straight line

Question 3

Changing gas temperature

Answer 3

• Increasing the temperature (at constant volume) of the gas causes the molecules to gain more kinetic energy
• This means that the particles will move faster and collide with the container walls more frequently
• The pressure of the gas increases
• The temperature is therefore directly proportional to the pressure (at constant volume)
• —A graph of temperature of gas plotted against pressure gives a straight line

Question 4

The kinetic theory of gases states that

Answer 4

molecules in gases are constantly moving

• The theory makes the following assumptions:
• The gas molecules are moving very fast and randomly
• The molecules hardly have any volume
• The gas molecules do not attract or repel each other (no intermolecular forces)
• No kinetic energy is lost when the gas molecules collide with each other (elastic collisions)
• The temperature of the gas is related to the average kinetic energy of the molecules

Question 5

ideal gases def

Answer 5

Gases that follow the kinetic theory of gases

Question 6

The volume that an ideal gas occupies depends on:

Answer 6

Its pressure

Its temperature

Question 7

Limitations of the ideal gas law

Answer 7

-At low temperatures and high pressures real gases do not obey the kinetic theory

Question 8

Real gases therefore do not obey the following kinetic theory assumptions at low temperatures and high pressures:

Answer 8

• There is zero attraction between molecules (due to attractive forces, the pressure is lower than expected for an ideal gas)
• The volume of the gas molecules can be ignored (volume of the gas is smaller than expected for an ideal gas)

Question 9

At low temperatures and high pressures real gases do not obey the kinetic theory as under these conditions:

Answer 9

• Molecules are close to each other
• There are instantaneous dipole- induced dipole or permanent dipole- permanent dipole forces between the molecules
• These attractive forces pull the molecules away from the container wall
• The volume of the molecules is not negligible

Question 10

Ideal gas equation

Answer 10

pV = nRT

• p = pressure (pascals, Pa)
• V = volume (m3)
• n = number of moles of gas (mol)
• R = gas constant (8.31 J K-1 mol-1)
• T = temperature (kelvin, K)
• The ideal gas equation can also be used to calculate the molar mass (Mr) of a gas

Question 11

Calculating the volume of a gas

Answer 11

Step 1: Rearrange the ideal gas equation to find volume of gas
Step 2: Calculate the volume the oxygen gas occupies

Question 12

Lattice Structures

Answer 12

• Most ionic, metallic and covalent compounds are crystalline lattice
• The ions, atoms or molecules are arranged in a regular and repeating arrangement

Question 13

Giant ionic lattices

Answer 13

• Ionic compounds are arranged in giant ionic lattices (also called giant ionic structures)
• The type of lattice formed depends on the sizes of the positive and negative ions which are arranged in an alternating fashion

Question 14

Covalent lattices

Answer 14

-Covalent compounds can be arranged in simple molecular or giant molecular lattices

• -Simple molecular lattices: Iodine, buckminsterfullerene (C60) and ice
• -Giant molecular: silicon(IV) oxide, graphite and diamond

Question 15

Metallic lattices

Answer 15

• Metals form giant metallic lattices in which the metal ions are surrounded by a ‘sea’ of delocalised electrons
• The metal ions are often packed in hexagonal layers or in a cubic arrangement

Question 16

Effects of Bonding & Structure on Physical Properties

Answer 16

Different types of structure and bonding have different effects on the physical properties of substances such as their melting and boiling points, electrical conductivity and solubility

Question 17

ionic bonding and giant ionic lattice structures

Answer 17

• Ionic compounds are strong
• They are brittle as ionic crystals can split apart
• have high melting and boiling points
• Ionic compounds are soluble in water as they can form ion – dipole bonds
• Ionic compounds only conduct electricity when molten or in solution

Question 18

Ionic compounds are strong.why?

Answer 18

The strong electrostatic forces in ionic compounds keep the ions strongly together

Question 19

Ionic compounds have high melting and boiling points. why?

Answer 19

• The strong electrostatic forces between the ions in the lattice act in all directions and keep them strongly together
• Melting and boiling points increase with charge density of the ions due to the greater electrostatic attraction of charges
• Mg2+O2- has a higher melting point Na+Cl–

Question 20

Ionic compounds only conduct electricity when molten or in solution. why?

Answer 20

When molten or in solution, the ions can freely move around and conduct electricity
In the solid state they’re in a fixed position and unable to move around

Question 21

Metallic bonding & giant metallic lattice structures

Answer 21

• Metallic compounds are malleable
• Metallic compounds are strong and hard
• Metals have high melting and boiling points
• Pure metals are insoluble in water
• Metals can conduct electricity when in the solid or liquid state

Question 22

Metallic compounds are malleable. why

Answer 22

• When a force is applied, the metal layers can slide
• The attractive forces between the metal ions and electrons act in all directions
• So when the layers slide, the metallic bonds are re-formed
• The lattice is not broken and has changed shape

Question 23

Metallic compounds are strong and hard. why

Answer 23

Due to the strong attractive forces between the metal ions and delocalised electrons

Question 24

Metals can conduct electricity when in the solid or liquid state. why

Answer 24

As both in the solid and liquid state there are mobile electrons which can freely move around and conduct electricity

Question 25

Simple covalent lattices

Answer 25

• have low melting and boiling points
• —These compounds have weak intermolecular forces between the molecules
• —Only little energy is required to break the lattice
• Most compounds are insoluble with water
• —Unless they are polar (such as HCl) or can form hydrogen bonds (such as NH3)
• They do not conduct electricity in the solid or liquid state as there are no charged particles
• —Some simple covalent compounds to conduct electricity in solution such as HCl which forms H+ and Cl– ions

Question 26

Giant covalent lattices

Answer 26

• Giant covalent lattices have melting and boiling points
• The compounds can be hard or soft
• Most compounds are insoluble with water
• Most compounds do not conduct electricity however some do

Question 27

Giant covalent lattices: Giant covalent lattices have melting and boiling points. why

Answer 27

• These compounds have a large number of covalent bonds linking the whole structure intermolecular forces between the molecules
• A lot of energy is required to break the lattice

Question 28

Giant covalent lattices: The compounds can be hard or soft. why

Answer 28

• Graphite is soft as the forces between the carbon layers are weak
• Diamond and silicon(IV) oxide are hard as it is difficult to break their 3D network of strong covalent bonds

Question 29

Giant covalent lattices: Most compounds do not conduct electricity however some do. why

Answer 29

• Graphite has delocalised electrons between the carbon layers which can move along the layers when a voltage is applied
• Diamond and silicon(IV) oxide do not conduct electricity as all four outer electrons on every carbon atom is involved in a covalent bond so there are no free electrons available

Question 30

Vapour pressure

Answer 30

The pressure exerted by a gas molecules (made from liquid) in equilibrium with its liquid

Lower it’s vaporised pressure = stronger bonds (sometimes hydrogen) intermolecular bonds = high boiling and melting points