4. States Of Matter

Question 1

Explain the origin of gas pressure.

Answer 1

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

Question 2

What does changing gas volume do to the pressure

Answer 2

Decreasing the volume 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

Question 3

What effect does changing the gas temperature have on the pressure

Answer 3

Causes molecules to gain more kinetic energy meaning particles move faster and collide with the container walls more frequently and pressure of gas increases
The temperature is therefore directly proportional to the pressure

Question 4

What are the kinetic theory assumptions

Answer 4

Ideal gases have zero particle volume
Have no intermolecular forces of attraction

Question 5

What happens to ideal gasses at very high pressure and low temperatures

Answer 5

The real gases do not obey the kinetic theory as under these conditions:
The molecules are close together
There are instantaneous dipole-induced or permanent dipole-permanent dipole forces between the molecules
These attractive forces pull the molecules away from the container

Question 6

What is the ideal gas equation

Answer 6

pV=nRT
p- pressure
n- number of moles (moles)
R- gas constant (8.31 J K -1 mol -1)
T- temperature (kelvin, K)

Question 7

What is an ionic bond

Answer 7

An electrostatic force between a positively charged metal ion and a negatively charged non-metal ion

Question 8

Define ideal gas

Answer 8

A gas whose volume varies in proportion to the temperature and in inverse proportion to the pressure. Noble gases such as helium and neon approach ideal behavior because of their low intermolecular forces.

Question 9

What is an alloy

Answer 9

A mixture of two or more metals or a metal with a non-metal

Question 10

What is brass?

Answer 10

An alloy of copper and zinc

Question 11

Why is brass stronger than pure copper

Answer 11

Zinc ions are larger than copper ions. The presence of different sized metal ions creates an arrangement of the lattice less regular. This stops the layers of ions from sliding over each other so easily

Question 12

Properties of graphite

Answer 12

1. High melting and boiling points—-> there is strong covalent bonding throughout the layers of carbon atoms, a lot of energy is required to overcome these bonds
2. Softness—-> forces between the layers of carbon atoms are weak. The layers of graphite can slide over each other when a force is applied. The layers readily flake off.
3. Good conductor of electricity——> when a voltage is applied, the delocalized electrons can move along the layers

Question 13

Properties of diamond

Answer 13

1. High melting and boiling points—-> there is a strong covalent bonding throughout the whole structure. A lot of energy is needed to break these bonds and separate the atoms.
2. Hardness—-> diamond cannot be scratched easily because it is difficult to break the three dimensional network of strong covalent bonds
3. Does not conduct electricity——> all of the four outer electrons on every carbon atom are involved in covalent bonding. This means there are no free electrons to carry The electric current

Question 14

What are the properties of buckminsterfullerene

Answer 14

1. It has a relatively low sublimation point. It turns directly from the solid to the vapor state when heated to about 600 degrees. This is because there are weak intermolecular forces between each buckminsterfullerene molecule
2. It is relatively soft
3. It is a poor conductor of electricity
4. It is slightly soluble in solvents such as carbon disulfide and methylbenzene
5. It is more reactive than diamond and graphite. It reacts with hydrogen, fluorine, chlorine, bromine and oxygen

Question 15

Examples of simple molecular lattices

Answer 15

Buckminsterfullerine (C60) and ice

Question 16

Examples of giant molecular lattices

Answer 16

Silicon (Iv) oxide
Graphite
Diamond

Question 17

Describe the properties of ionic compounds

Answer 17

They are strong- strong electrostatic forces keep the ions strongly together
They are brittle as ionic crystals can split apart
High melting and boiling points
-melting and boiling points increase with charge density of the ions due to the greater electrostatic attraction of charges.

Question 18

Describe the properties of metallic compounds

Answer 18

They are malleable.
-when a force is applied the metal layers can slide, when they slide the metallic bonds are reformed
-the attractive forces between the metal ions and electrons act in all directions

They are strong and hard- due to the string attractive forces between the metal ions and delocalized electrons.

They have high melting and boiling points
Pure metals are insoluble in water
Can conduct electricity in the solid or liquid state- as there are mobile electrons which move freely and conduct electricity

Question 19

Describe the properties of simple covalent lattices

Answer 19

They have low melting and boiling points
-they have weak intermolecular forces between the molecules and only little energy is required to break the lattice.
They are insoluble in water unless they are polar and can form hydrogen bonds
They do not conduct electricity in solid or liquid state as there are no charged particles.

Question 20

Describe the properties of giant covalent lattices.

Answer 20

They have high melting and boiling points
- they have large numbers of covalent bonds linking the whole structure and intermolecular forces between the molecules so a lot of energy is required to break the lattice.
Compounds can be hard or soft
Most are insoluble in water
Most do not conduct electricity