module 5 - revision deck Flashcards
soluble ions
- all group 1 cations and NH4+ (no exceptions)
- Cl-, Br-, I- (except Ag, Pb, Hg)
- SO42- (except Ba, Pb, Ca, Hg)
insoluble ions
- SO32-, CO32-, PO43- (except group 1 and NH4)
- S2- (except all group 1, 2, and NH4+)
- O2- (except all group 1, Ba2+ and Ca2+)
- OH- (except all group 1, NH4+, Ba2+ and Ca2+)
cobalt chloride hydrated and dehydrated equation
[Co(H2O)6]2+ + 4Cl- –> CoCl42+ + 6H2O
pink –> blue
iron(III) nitrate and potassium thiocyanate
Fe3+ + SCN- –> [FeSCN]2+
pale yellow, colourless –> brown/red
open system
interacts with its environment, meaning that energy and matter are constantly moving between the system and the environment
closed system
energy can move between the system and environment, but matter cannot
static equilibrium
occurs when the forward and reverse reaction rates are both zero
dynamic equilibrium
when the forward and reverse reactions are happening at the same time and the same rate
characteristics of an equilibrium system
- closed system
- reversible reaction
- macroscopic properties stay constant
- concentrations of all reactants and products stay the same
- continuous changes at the atomic level
- equilibrium can be approached from either direction
combustion reactions
irreversible reaction that only proceeds in one direction and goes to completion. Exothermic reaction and most occur spontaneously
photosynthesis
irreversible endothermic reaction, not spontaneous. respiration looks like the reverse, but both photosynthesis and respiration go to completion and are not reversible
activation energy
- the energy needed to start a chemical reaction
- many reactions go to completion because of the low activation energy
- for a reaction to be reversible, both the products and reactants need to have enough energy to react
le châtelier’s principle
if a system is in equilibrium, and it is disturbed or changed in any way, then the system will adjust itself to minimise the amount of change
interaction between nitrogen dioxide and dinitrogen tetroxide
2NO2(g) –> N2O4
delta H < 0
effect of temperature on equilibrium
increasing temperature shifts equilibrium towards the endothermic reaction, and decreasing temperature will shift equilibrium towards the exothermic reaction
effect of concentration on equilibrium
increasing the concentration of reactants will favour the reaction forming products, and increasing the concentration of products will favour the reaction forming reactants
effect of volume/pressure on equilibrium
increasing pressure will shift equilibrium towards the side of the reaction with fewer moles of gas, and decreasing pressure will favour the side of the reaction with more molecules of gas.
gases must be present for pressure to have an effect
effect of catalyst on equilibrium position
catalysts have no effect on equilibrium position, but the reaction will reach equilibrium faster
Keq
products/reactants
reaction quotient Q
if Q=Keq then system at equilibrium
Q < Keq, forward reaction favoured
Q > Keq reverse reaction favoured
keq and equilibrium position
Keq > 1 indicates that equilibrium lies to the right
Keq < 1 indicates that equilibrium lies to the left
temperature on equilibrium expression
exothermic: as temp increases, Keq decreases
endothermic: as temp increases, Keq increases
dissolution of ionic compounds in water
solute dissolves when the energy of the bonds it forms with water are lower than the energy of the bonds between water molecules, or between the ions of the substance being dissolved
cycad fruit equilibrium stuff
Ksp
the product of the concentration of each ion in a saturated solution of a sparingly soluble salt at 298K, raised to the power of their stoichiometric coefficients
the higher the Ksp, the more soluble the salt is
predicting the formation of precipitates using Ksp
if the product of the concentrations of ions > Ksp, the solution is saturated and a precipitate forms
if the product of the concentrations of ions < Ksp, the solution is unsaturated and no precipitate forms
common ion effect
when two solutions are mixed and they contain a common ion, the solubility of any precipitate forming is reduced
