Topic 1: Stoichiometric Relationships

A sample substance composed of a single type of atom

Atoms of the same element, having the same no. of protons, but with differing no. of neutrons

• molecules made up of atoms of various elements - they chemically combine together in a fixed ratio

• mixture of elements/compounds • they are not chemically bonded • so the individual components retain their individual properties

mixture in which all components are in the same state e.g. all gases

mixture in which components are in different states e. g. - a solid and a liquid - 2 immiscible liquids, like oil and water

A liquid in an enclosed chamber will form a dynamic equilibrium with its own vapor: • fast-moving particles in the liquid escape and become vapor • slow-moving particles in the vapor becomes part of the liquid

• as temp. increases, average speed of particles increases - so as temp. increases, equilibrium vapour pressure also increases

A measure of the energy change when 1 mol of liquid converts to gas at standard pressure

b.pt of a liquid is determined by the temp at which vapour pressure = atmospheric pressure Elaboration: food in a pressure cooker is cooked faster because of the alteration in boiling point (70 degrees Celsius instead of 100)

The amount of substance containing the same number of atoms as in exactly 12g of the isotope C-12

• unit: Ar The average mass of an atom of the element, taking into account all the isotopes and their relative abundance, as compared to 1 atom of C-12

• unit: Mr - sum of the relative molecular mass of all the atoms in a molecule

sum of the relative formula mass of all the atoms in one unit of an ionic compound

• empirical formula • molecular formula • structural formula

• simplest whole number ratio of the atoms of all element in one molecule of the compound

• shows the real number of atoms of all elements in one molecule of the compound

no. of moles = mass* / molar mass * % mass can also be used here.

shows arrangements of atoms and bonds in a molecule

• Record the weight of a crucible • Place the compound (e.g. magnesium ribbon) inside the crucible and weigh it • Put the crucible on a clay triangle and strongly heat until the magnesium ribbon begins to burn • Lift the lid slightly to allow air to enter and continue until all the magnesium has burned (to form MgO2) • Allow the crucible to cool and weigh it • If you have common sense and can do basic arithmetic, please utilize those skills here.

an equal vol. of gases, both measured at the same temp. and pressure, contain an equal no. of particles. v1/n1 = v2/n2 v: volume n: no. of particles/moles

• no attractive forces between gaseous particles • KE of particles are directly proportional to temp • follows the kinetic particle theory 100%

when the temp is high and pressure is low

lower temp → less movement → stronger intermolecular forces