States of matter and reaction kinetics

States of Matter

Ideal Gases:

The ideal gas equation is PV = nRT

Where

P is pressure in Pascals
T is the temperature in kelvin
V is the volume in m
N is the number of moles of the gas

Origin of pressure:

Gas molecules are in constant random motion
They vibrate and collide with the internal wall of a container
They exert a force on the inner wall
The exerted force results in pressure

The basic assumption of ideal gases:

Molecules behave as a rigid sphere
There are no/ negligible intermolecular forces
Collisions between particles are perfectly elastic
The molecules have no volume
Molecules are in constant random motion

Few formulas:

P V = P V (Only applicable for constant temperature).

(Applicable for changing temperature)

Practise Questions:

A flask of volume 5dm contains 4g of oxygen. Calculate the pressure exerted by the gas at a temperature of 127°
A flask of volume 2dm was found to contain 5.28g of gas. The pressure in the flask is measured and it was 200kPa.Temperature of the flask was 20°C. Calculate the relative molecular mass of gas.

3. Flask M contains Helium at 20°C at a pressure of 1x10 Pa. N has been evacuated and has three times the volume of M.in an experiment, the valve is opened and the temperature of the whole apparatus is raised to 100°C.

Calculate the final pressure of the system.

3

1

2

5

3

Neon Nitrogen Ammonia

From Neon to Ammonia ideal behaviour decreases.
Nitrogen has stronger intermolecular forces than Neon
Ammonia has hydrogen bonding which is the strongest in simple molecular compounds.

Two conditions are necessary for gas to reach ideal behaviour:

High temperature
Low pressure

These two condition ensure molecules have lower intermolecular forces between them.

Relationship between PV and P for a real gas at two different temperatures.

T1 is at a lower temperature as it shows greater divination from the ideal properties

They are due to the following reasons:

Reducing temperature reduces the kinetic energy of particles
Intermolecular forces become more significant

Higher the pressure the greater the deviation from the ideal property:

Increasing pressure decreases the volume
The volume of particles becomes more significant

The formula for overall pressure calculation:

Example:

Flask X contains 5dm of Helium at 12KPa and another flask Y contains 10 dm of Neon at 6Kpa pressure.

If the flasks are connected at constant temperature, what will be the final pressure?

3

Giant Molecular Compounds

Silicon Dioxide/Silicon(IV) oxide

One silicon atom makes four covalent bonds with four oxygen atoms.
One oxygen molecule makes two covalent bonds with two silicon atoms.
There are no delocalised electrons.
Atoms are arranged tetrahedrally.
It is insoluble in water or inorganic solvent.
It has high melting and boiling point due to its giant molecular structure and strong covalent bonds.

2. Graphite

Layered structure.
The layers are in a hexagonal shape.
Weak intermolecular force/van der Waals force of attraction between layers.
Layers can slide over each other which makes it lubricative.
It can conduct electricity due to the presence of free electrons.
It has high melting and boiling point due to its giant molecular structure and strong covalent bonds.
It is insoluble in water or inorganic solvent.

3. Diamond

One carbon atom is bonded to four carbon atoms.
Atoms are arranged tetrahedrally.
No free electrons.
It is insoluble in water or inorganic solvent.

** Diamond, Graphite and Fullerene are allotropes of Carbon

4. Buckminsterfullerene (C60):

It has a simple molecular structure
It has the shape of a hollow sphere.
The C60 molecule has carbon atoms that are arranged at the corners of 20 hexagons and 12 pentagons.
Some electrons are delocalised.
It has a low melting point.

Reaction kinetics

Rate = Change in concentration of reactants or products per unit time.

Factors affecting the rate of reaction.

Temperature
Pressure (only for the reaction of gases)
Concentration
The surface area of reactants

Effect of temperature

The rate of reaction increases with the increase in temperature because

Particles have more Kinetic energy
As a result, they move faster
They collide more frequently
The number of effective collisions increases.
Less time is needed to complete the reaction.

Effect of pressure

The rate of reaction increases with the increase of pressure because

The molecules are closer together.
This results in more gas molecules per unit volume.
Frequency of collision increases
The number of successful collisions increases.

Effect of concentration

The rate of reaction increases with the increase of concentration of reactants as

There are more particles per unit volume
The particles collide more frequently
The number of successful collisions is greater.

Effect of surface area

The rate of reaction increases with the increase of surface area because

More reactants are exposed to react
The reactants collide more frequently
The number of successful collisions increases

Catalyst

A substance that can speed up a chemical reaction by lowering the activation energy by creating an alternative route.

A catalyst remains unchanged after the chemical reaction has been completed.
Catalyst can NOT change the yield of a reaction.
Catalyst cannot change the value of enthalpy change(ΔH).
Catalyst cannot change the position of equilibrium.
Catalyst can be both organic and inorganic substance