UNIT 11:STATES OF MATTER

Bonds versus intermolecular forces

Intra versus InterMolecular

An intramolecular force is any force that holds together the atoms making up a molecule or compound.

Intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules or ions). They are weak compared to the intramolecular forces, the forces which keep a molecule together.

Types of Intermolecular forces The London dispersion force is the

weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction.

More intermolecular forces

Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.

The last of the intermolecular

A hydrogen bonding is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge.

Dipole?

This happens in covalent molecules, remember non-metal to non-metal Dipole is when an atom is very

electronegative and another atom that is significantly lower in electronegativity.

Examples are oxygen to hydrogen, Fluorine to hydrogen, not carbon to hydrogen

The very electronegative element pulls the electrons away from the less electronegative element, making a dipole moment in the molecule

Water and its properties

Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the oxygen family in the periodic table, which are gases such as hydrogen sulfide.

The elements surrounding oxygen in the periodic table, nitrogen, fluorine, phosphorus, sulfur and  chlorine, all combine with hydrogen to produce gases under standard conditions. The reason that water forms a liquid is that oxygen is more electronegative than all of these elements with the exception of fluorine. Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom.

continued

Because of the strong opposites of the oxygen and hydrogen, water attracts other water molecules and other dipole molecules and ionic compounds.

Boiling and melting point The stronger the bond, the more the

bonds between molecules will affect the melting point or boiling point.

Temperature

Temperature is the measure of kinetic energy. The more motion the higher the temperature, the less motion the lower the temperature.

Absolute zero is the definition of no motion.

Amount of heat transferred to a system

Q=amount of heat absorbed M=mass in grams c=specific heat (Heat required to change

the temperature of a substance by one degree)

T=temperature in degrees Celcius q=ΔH only for constant pressure

The enthalpy change that accompanies the heating/cooling of a pure substance is determined by the equation:

  ∆H = mCp∆T   where: ∆H = the change in enthalpy (positive for heating, negative for cooling) m = the mass of the thing being heated (in grams) Cp = the specific heat / heat capacity – the amount of energy needed to heat the

thing by 10 C. ∆T = the change in temperature (in degrees Celsius).   Sample problems:   How much energy will be needed to heat 45 grams of ethanol (Cp = 2.44 J/g0C) from 200

C to 400 C? 2196 J If burning a single match gives off 250 J, how much hotter can it make a 50 gram block

of silver (Cp of silver is 0.235 J/g0C) 21.30 C  

Heating curves

Definitions for the heating curves

=amount of heat or energy required to fuse molecules together such as freezing. The negative or opposite of fusing would be melting.

amount of heat or energy required to vaporize molecules or molecules to escape their intermolecular forces to become gases.

Both of these heats are when the molecules are undergoing a phase change

At the point of change all energy is used to break intermolecular bonds and they will NOT increase their temperature at this time.

Kinetic molecular theory

The kinetic theory of gases describes a gas as a large number of small particles (atoms ormolecules), all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container.

Dynamic equilibrium

A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state.

In other words, the ratio between products and reactants goes up then down, then up then down, never stoping

Melting-freezing, vaporization-condensation back and forth

Phase diagram

Temperature versus pressure.Phases depend on pressure, and temperature