The Chemical Industry Flashcards
What is the structure of N2? Where are the lone pairs?
It is N≡N. It is two nitrogens that have a triple bond.
Each nitrogen has a lone pair
What is the bond enthalpy of N≡N? What does this mean for the activation enthalpies for reactions involving N2?
It is very large 945kJmol-1
The activation enthalpy is therefore very high
What is the reaction to form ammonia?
N2 + 3H2 ==> 2NH3
What is the structure of NH3?
It has 3 hydrogen-nitrogen bonds and one lone pair.
How is NH4+ formed?
The lone pair on the nitrogen attracts a H+ ion and this forms a NH4+ ammonium ion
What type of bond is formed when NH3 reacts with H+?
The bond that is formed is a dative covalent bond. The nitrogen donates two electrons
What is the appearance and where does it come from for:
a) nitrogen oxide (NO)
b) nitrogen dioxide (NO2)
c) dinitrogen oxide (N2O)
a) NO is a colourless gas that turns into NO2 when in air. It comes from combustion in vehicles, thunderstorms and from denitrifying bacteria
b) NO2 is a brown gas and forms from the oxidation of NO
c) N2O is a colourless gas that is formed in the soil by denitrifying bacteria
What is the equation for the creation of nitrogen oxide?
N2 + O2 ==> 2NO
What is the shape and bonding of nitrate(III)? How common is it?
Two oxygens bonded to a nitrogen(III) a single bond and then both of the oxygens share a delocalised bond to the nitrogen. The nitrogen has a lone pair.
It is not very common.
What is the shape and bonding of Nitrate(V)? How common is it?
It is made from a nitrogen(V) with 3 oxygens joined by a single bond. and then all the oxygens are joined to the nitrogen by another delocalised bond.
Are NO3- and NO2- soluble in water?
They are very soluble
How are NO2- made from NH4+? What is the name of the process?
NH4+ + 1.5O2 ==> NO2- + 2H+ + H2O
The process is called nitrification
How is NO3- made? What is the name of this process?
NO2- + 0.5O2 ==> NO3-
This is oxidation
How can you test for nitrate ions?
You react the nitrate ions with sodium hydroxide with Devardas alloy and an aluminium complex and ammonia is produced and this can be tested with litmus paper and turn it blue.
3NO3- + 8Al + 5OH- + 18H2O ==> 3NH3 + 8[Al(OH)4]-
What is Devardas alloy?
It is an alloy of Cu, Al and Zn
What is another test for ammonia?
When it comes into contact with hydrogen chloride gas it forms a white smoke
How can ammonium ions (NH4+) be tested for?
When reacted with sodium hydroxide it will produce ammonia which can be tested.
NH4+ + OH- ==> NH3 + H2O
What is the equilibrium constant? What is the symbol?
This is the measure of the position of equilibirum
Sumbol: Kc
What is the equation for the equilibrium constant for the reaction aA + bB <=> cC + dD?
Kc = [C]^c [D]^d / [A]^a [B]^b
Products / reactants
How much does the equilibrium constant vary?
Greatly
How does increasing the pressure change the position of equilibrium?
It moves the position of equilibrium to the side with the fewer gas molecules. This is because the reaction want to reduce the pressure.
What is Le Chateliers principle with regards to the position of equilibrium?
The position of equilibrium changes as to counteract the change in pressure as much as possible so that the magnitude of Kc can stay constant.
What happens to the position of equilibrium when the pressure is increased for the reaction of:
CH4 + H2O <=> CO + 3H2
It moves to the left because there are fewer gas molecules
What happens to the position of equilibrium when pressure is increased for the reaction of:
CO + 2H2 <=> CH3OH
It moves to the right because there are 3 gas molecules on the left and 1 on the right
Is the value of Kc affected by a change in pressure or concentration? (comparing before and after)
No, because the reactions counters the change keeping Kc constant
Does temperature affect the value of Kc?
Yes
For an increase in temperature, which direction is favoured for an endothermic reaction?
The products
For an increase in temperature, which direction is favoured for an exothermic reaction?
The reactants
How does a catalyst affect the position of equilibrium?
It has no effect
What are some examples of how to measure the position of equilibrium?
pH measurements
Colorimetric methods
Titrations
What is the rate of a reaction?
This is the rate at which the reactants form products
What is the key way factor that changes during a reaction as it progresses?
The concentrations of the products and the reactants
What is the rate of formation of products when compared with the rate of consummation of reactants?
The same
What is the equation to determine the rate of a reactions?
Rate = Change in property / time
What properties of a reaction can be measured to determine the rate? Which interfere with the reaction? (5)
Volumes of gases evolved Measuring mass change pH measurements Colorimetry Chemical analysis*
- interferes with the reaction
How can the volume of gas evolved be measured?
Using an upturned cylinder or gas syringe
How can the mass change be measured?
By placing the reaction on a balance
How can colorimetry be used to measure the rate of a reaction?
The colour can be measured through out the reaction and plotted on a graph