4 STATES OF MATTER [must REVIEW; only online] Flashcards
gases in container … (2)
-exert a pressure
- as the gas molecules are constantly colliding with the wall of the container
changing VOLUME (3)
-decreasing volume (at constant temp) => the molecules are squashed together => more frequent collisions with the container wall
- so pressure of the gas increases
relationship & graph
btwn volume & pressure.
-so volume is inversely proportional to pressure (at constant temperature)
- graph of the volume of gas plotted against 1/pressure gives a straight line
([1 ÷ pressure] directly proportional to volume)
changing temp (3)
-increasing temp (at constant volume) causes molecules to gain more kinetic energy => particles will move faster and collide with container walls more frequently
- pressure of the gas increases
relationship btwn temp & volume of gas
-so temperature is directly proportional to the pressure (at constant volume)
- graph of the temperature of gas plotted against pressure gives a straight line
Kinetic theory of gases states what?
molecules in gases are constantly moving
what assumptions does the kinetic theory of gases make? [5]
- gas molecules are MOVING very FAST and RANDOMLY
-molecules HARDLY have any VOLUME
-gas molecules do NOT attract or repel each other (no intermolecular forces, no IMF)
-No kinetic energy is lost when the gas molecules collide with each other (ELASTIC collisions)
-temperature of the gas is related to the average kinetic energy of the molecules
so what are ideal gases? (3)
they have zero particle volume and no intermolecular forces of attraction (OR repulsion),
so they follow the kinetic theory of gases
& what are real gases?
in reality, gases do not fit this description exactly but real gases may come very close
changing TEMP,
constant pressure
INCREASES the volume.
-gas is heated (at constant pressure), particles gain more kinetic energy and undergo more frequent collisions with the container wall
-to keep pressure constant, molecules must get further apart and so the volume increases
-so volume is directly proportional to the temperature (at constant pressure)
Limitations of the ideal gas law,
under what conditions do these limitations arise?
very high pressures and low temperatures,
real gases do not obey the kinetic theory.
why high pressure, low temp limits ideal gas law?
-Molecules close to each other
-there are instantaneous dipole- induced dipole or permanent dipole- permanent dipole forces between molecules
-attractive forces pull molecules away from the container wall
-volume of the molecules is not negligible
so what assumptions are not followed by real gases?
at high temperatures and pressures,
-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)
Ideal gas equation
(can also be used to calc molar mass, Mr, of a gas)
pV = nRT
p = pressure (pascals)
V = volume (m3)
n = number of moles of gas (mol)
R = gas constant (8.31 J K-1 mol-1)
T = temp (kelvin)
e.g v=?, n = 0.781mol, p = 220kPa = 220 x 10^3 Pa, temp = 21 Celsius = 294.15K
V = nRT/p = 0.781 x 8.31 x 294.15 / 220 x 10^3 =0.00868 or 0.00867 m^3 to dm^3 will be x1000
= 8.67 dm^3
celsius to k
celsius + 273 = kelvin
relationships for ideal gas + graph
an ideal gas will have a volume that is directly proportional to the TEMPERATURE and inversely proportional to the pressure.
IONIC
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
The ionic lattice of MgO and NaCl are cubic
COVALENT lattices (simple molecular OR giant molecular lattices)
examples
Simple molecular lattices: Iodine, buckminsterfullerene (C60) and ice
Giant molecular: silicon(IV) oxide, graphite and diamond
metallic lattices
metal ions are often packed in hexagonal layers or in a cubic arrangement
Ionic bonding & giant ionic lattice structures - structure & properties
- Ionic compounds are strong. Strong electrostatic forces in ionic compounds keep the ions strongly together
-are brittle as ionic crystals can split apart
- Ionic compounds have high melting and boiling points. 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
- e.g, Mg2+O2- has a higher melting point Na+Cl-
📍Ionic compounds are soluble in water as they can form ion - dipole bonds
- Ionic compounds only conduct electricity when molten or in solution; ions can freely move around and conduct electricity. In the solid state they’re in a fixed position and unable to move around
Metallic bonding & giant metallic lattice
📍Metallic compounds are malleable. 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
📍Metallic compounds are strong and hard, due to the strong attractive forces between the metal ions and delocalised electrons.
📍Metals have high melting and boiling points
Due to the strong attractive forces between the metal ions and delocalised electrons
The greater the number of delocalised electrons and the smaller the cation, the greater the attractive force between them resulting in a higher melting / boiling point
📍Pure metals are insoluble in water
📍Metals can conduct electricity when in a solid or liquid state; mobile electrons which can freely move around and conduct electricity
SIMPLE covalent lattice
📍Simple covalent lattices have low melting and boiling points; 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. BUT Some simple covalent compounds conduct electricity in solution such as HCl which forms H+ and Cl- ions
GIANT covalent lattice
📍Giant covalent lattices have high melting and boiling points; compounds have a large number of covalent bonds linking the whole structure and intermolecular forces between the molecules. A lot of energy is required to break the lattice
📍The compounds can be hard or soft. 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
📍Most compounds are insoluble in water
📍Most compounds do not conduct electricity however some do.
-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 are involved in a covalent bond so there are no free electrons available
