CI Flashcards
nitrogen gas is unreactive because
it contains a triple bond, high bond enthalpy, therefore large amount of energy required to break triple bond
bonding in ammonia
chemical formula NH3, sigma bonds between nitrogen and each hydrogen, lone pair on hydrogen (therefore tetrahedral shape)
ammonium ions
lone pair in ammonia forms dative covalent bond with a proton
nitrate III
NO2-
charge is delocalised over the two N-O bonds
nitrate V
NO3-
dative covalent bond to one of the hydrogen atoms
solubility of nitrates
very soluble in water
nitrification
oxidation of ammonium ions in the soil to form nitrates by nitrifying bacteria
3/2(O2) + NH4+»_space; NO2- + H20 + 2H+
NO2- + 1/2(O2)»_space; NO3-
test for nitrate V
NaOH and Devarda’s alloy added to test solution
gently heated
aluminium acts as reducing agent
if nitrate V present, ammonia gtas evolved
effect of ammonia gas on damp litmus paper
turns from red to blue
testing for ammonium ions
NaOH added to test solution
gently heated
if ammonium ions are present, ammonia gas is evolved
effect of increase in pressure on equilibrium and Kc
equilibrium shifts to side producing fewest moles of gas to counteract change in pressure
Kc remains unchanged
effect of catalyst on position of equilibrium and Kc
no effect on either
rate of reaction
rate of converting reactants to products
can be expressed as rate of reactant used or rate of product formed
general rate equation
rate = k [A]^m [B]^n
m = order of reaction with respect to A n = order of reaction with respect to B
overall order of reaction
order of reaction with respect to A + order of reaction with respect to B
( m + n )
units of overall order of reaction
zero order = moldm-3 s-1
first order = s-1
second order = dm3 mol-1 s-1
finding order with respect to a reactant
carry out the reaction several times, varying concentration of 1 reactant
use tangent to each progress curve to calculate initial rate at each concentration
plot initial rate against concentration to determine order with respect to reactant
using half life to determine order of reaction with respect to reactant
plot progress curve (reactant used/product formed against time)
calculate half lives
if constant then reaction is first order
rate equation can tell you:
gives info about the slowest step in the reaction (rate determining step)
indicates what substances in the reaction are and aren’t involved in the rate determining step
order of reaction for each substance indicates relative number of moles of each substance involved in the rate determining step
substance with zero order in rate equation
not involved in rate determining step
why are some steps slow?
steps have different Ea (activation enthalpy)
large Ea means only a small number of species have enough energy to react and form products
