Topic 1: Stoichiometric Relationships Flashcards
element
A sample substance composed of a single type of atom
isotope
Atoms of the same element, having the same no. of protons, but with differing no. of neutrons
compound
- molecules made up of atoms of various elements
- they chemically combine together in a fixed ratio
mixture
- mixture of elements/compounds
- they are not chemically bonded
- so the individual components retain their individual properties
homogeneous mixture
mixture in which all components are in the same state
e.g. all gases
heterogeneous mixture
mixture in which components are in different states
e. g. - a solid and a liquid
- 2 immiscible liquids, like oil and water
Outline the liquid-vapour equilibrium
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
Effect of temperature on vapor pressure
- as temp. increases, average speed of particles increases
- so as temp. increases, equilibrium vapour pressure also increases
Define the enthalpy of vaporisation
A measure of the energy change when 1 mol of liquid converts to gas at standard pressure
What is the relationship between the boiling point of a liquid and the vapor-atmospheric pressure equilibrium?
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)
mole
The amount of substance containing the same number of atoms as in exactly 12g of the isotope C-12
relative atomic mass
- 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
relative molecular mass
- unit: Mr
- sum of the relative molecular mass of all the atoms in a molecule
relative formula mass
sum of the relative formula mass of all the atoms in one unit of an ionic compound
types of molecular formulas
- empirical formula
- molecular formula
- structural formula
empirical formula
- simplest whole number ratio of the atoms of all element in one molecule of the compound
molecular formula
- shows the real number of atoms of all elements in one molecule of the compound
how to obtain the empirical formula of a molecule
no. of moles = mass* / molar mass
* % mass can also be used here.
structural formula
shows arrangements of atoms and bonds in a molecule
how to experimentally determine empirical formula
- 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.
Avogadro’s Law
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
ideal gas concept
- no attractive forces between gaseous particles
- KE of particles are directly proportional to temp
- follows the kinetic particle theory 100%
when are real gases closest to the ideal gas concept?
when the temp is high and pressure is low
how temperature affects real gases
lower temp → less movement → stronger intermolecular forces
how pressure affects real gases
higher pressure → molecules move closer to each other → stronger intermolecular forces
ideal gas equation
PV = nRT
P: pressure V: volume n: no. of moles R: ideal gas constant T: temp (MUST BE IN KELVIN)
Boyle’s law
at constant temp , pressure is inversely proportional to volume
P1V1 = P2V2
gas law
P1V1 / T1 = P2V2 / T2
OR
PV/T = a constant
how to calculate yield from reaction equations
- Obtain the stoichiometric values of the reaction (molar coefficients of each compound)
- Use mole equations to find the limiting reagent
- You can find the max yield from there
solutions and concentration equation
conc x vol = amount of solute
dilution of solutions equation
c1v1 = c2v2 c = conc V = vol
mole equations
no. of moles = no. of particles / Avogadro’s constant
no. of moles = mass / molar mass
no. of moles = mass / molar vol
no. of moles = concentration x volume
law of conservation
matter can neither be created nor destroyed, it can only be changed from one form to another
gas and molar volume relationship
- all gases under same conditions have same molar volume
e. g. STP/RTP
why is beer stored in cold places?
- they can burst if kept in hotter conditions!
higher temp = higher pressure
back-titration
- technique used to analyse the unknown conc. of a solution
- indirectly measures amount of limiting reactant
atom economy
- measure of the amount of reactants that become useful products
- ideally no atom should be wasted
how does knowledge of atom economy help chemists?
higher atom economy → fewer resources used → less waste
how to calculate atom economy
100 x (total mass of desired products) / (total mass of all products)
