The Chemical Industry Flashcards
What type of chemistry do many nitrogen compounds + ions play an important role in?
Soil chemistry
What is the systematic name, appearance, and oxidation state of nitrogen in the compound N2O?
Dinitrogen oxide
+1
Colourless gas
What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO?
Nitrogen oxide
+2
Colourless gas
What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO2?
Nitrogen dioxide
+4
Brown gas
How is nitrogen (II) oxide formed from nitrogen?
N2 (g) + O2 (g) → 2NO (g)
How is nitrogen (IV) oxide formed from nitrogen (III) oxide?
What colour is the product?
2NO(g) + 2O2 (g) → 2NO2 (g)
Brown gas formed
Which nitrate do anaerobic bacterua reduce during respiration?
Nitrate (V)
What is the equation/sequence for anaerobic respiration in nitrogen-respiring bacteria?
NO2-(aq) → NO(g) → N2O(g) → N2 (g)
Why is ammonia able to act as a base?
Lone pair is able to accept H+ to become ammonium ion
NH3 + H+ → NH4+
What is nitrate (V) often known as?
Just nitrate
What is the molecular formula, bond angle, and diagram for nitrate (V) ions?
NO3-
120º - Triangular Planar
What are the properties of nitrate (V) ions?
Lone pairs form dative covalent bonds to O therefore increases oxidation no.
Very soluble in water
What is the molecular formula, bond angle, and diagram for nitrate (III) ions?
NO2-
120º - Triangular planar
What are the properties of nitrate (III) ions?
Very soluble in water.
Can use lone pair to form dative covalent bonds
2 ressonance forms
What are the properties of diatomic nitrogen?
Very strong triple bond - low reactivity.
High bond enthalpy.
Why is it not possible to test for compounds containing nitrate (V) or ammonium ions using precipitation?
What type of tests must be used instead?
They are all soluble
Must use tests involving formation of ammonia gas instead
What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonia?
-3
Trigonal pyrimidal
107º
What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonium?
-3
Tetrahedral
109.5º
Describe the test for ammonium ions
Substance being tested warmed with added NaOH.
If ammonium present, ammonia gas formed + will turn damp red litmus blue
What is the equation for the test for ammonium ions?
NH4+(aq) + OH-(aq) → NH3 (g) + H2O(l)
What is the test for nitrate (V) ions?
Added NaOH + spatula of Devarda’s alloy (mis of Cu, Al, Zn) + heat gently
Ammonia gas formed + will turn damp red litmus blue
Other than using damp red litmus, how can you test for ammonia gas?
Using conc. HCl as when fumes mixed produces white ammonium chloride gas
What are the interconversions of nitrogen compounds important in maintaining?
The balance of nutrient ions (e.g. nitrate (V)) in the soil
Give the definition of a catalyst
Substance that speeds up the rate of reaction by providing an alternate reaction pathway with a lower Ea
What is the equation for Kc?
[C]c[D]d
[A]a[B]b
AKA Products over Reactants
If the concentration of reactant(s) is changed, how is the position of equilibrium, Kc, and rate affected?
The position of equlibium is changed to oppose change - favours side with lower conc.
Kc is unchanged
The rate is changed as only rate at which equilibrium reached changed.
If the total pressue of a reaction is changed, how is the position of equilibrium, Kc, and rate affected?
Position of equilibrium may change in order to keep ratio of reactants + products same
Kc unchanged
Rate may change
If the the temperature of a reaction is changed, how is the position of equilibrium, Kc, and rate affected?
The position of equilibrium will change to favour the endo/exo side depending on if temp increased/decreased
Kc will change (temp only factor that changes it)
Rate changed due to position changing
How does a catalyst affect the position of equilibrium, Kc, and rate?
Position of equlibrium is unchanged
Kc unchanged
Only rate at which equilibrium reached changed, not composition (Kc)
What is the only factor that affects the magnitude of Kc?
Temperature
How can the units of Kc be found?
By substituting them into the equilibrium equation
What is it important to remember when calculating the units for Kc?
Must be calcuted in every case (won’t necessarily be the same)
May have no units
How may mol-2dm6 also be written?
1/(moldm-3)2
What techniques can be used to determine equilibrum constants/how?
First necessary to determine the conc. substances involved
e.g. by titration if one substance is acidic
Conc other substances can then be deduced from molar ratio
Aside from titration, what other experimental techniques can be used to determine equilbrium constants?
Spectroscopic or calorimetric methods
What is stoichiometry?
Molar ratio of reactants + products in a chemical equation
What general equation can be used to calculate rate of reaction?
change in property (e.g conc reactant) /
Time taken
What are the units for rate of reaction usually?
moldm-3s-1
(applies if change in conc. of smth being measured)
What characteristics/changes in a reaction can be monitored to identify/measure rate directly?
How can they be monitored?
Vol. gas evolved from a gas syringe
Mass change using a balance
pH change using a pH meter
Colour changes using a colorimeter
Complete the sentence:
Quenching uses ____ _____ as conc. reactants/products determined via titration
Chemical analysis
What quenching is and how it can be used to determine rate?
Effectively stops progress of reaction by slowing rate down suddenly.
Allows composition/progress of reaction to be analysed (e.g. by titration)
Can be done by adding large amounts water or neutralising
Describe how colorimetry can be used to determine the concentration of an unknown sample
- Make up series of standard solutns of known conc
- Select filter with complimentary colour to test solutns
- Zero the colorimeter with pure solvent (e.g water)
- Measure the absorbance of the standard solution + plot a calibration curve showing conc vs. abs.
- Measure the absorbance of the test solutn + read off the conc from the calibration curve
Describe the structure of a colorimeter
Narrow bean of light
Filter/diffraction grating selects light of wavelengths absorbed by solutn (is complimentary colour)
Solution under test
Photocell
Sensitive meter
What is the overall order of reaction?
The sum of orders of reaction for each individual reactant
What is the rate equation?
Mathmatical equation which enables the rate of reaction to be calculated
In the form: rate = k[A]m[B]n
What cannot be used to determine the rate equation?
What must be used instead?
Cannot predict rate equation from balanced equation
Must use experimental data
If a reactant is zero order, what is the effect of doubling the conc of the reactant on the rate of reaction?
No effect
rate ∝ [A]0
If a reactant is first order, what is effect does doubling its conc have on the rate of reaction?
Rate doubled when conc doubled
rate ∝ [A]1
If a reactant is second order, what happens to the rate of reaction when its conc is doubled?
Rate quadrupled when conc doubled
rate ∝ [A]2
If a substance is zero order, what doesn’t it appear in/befre?
The rate determining step
How can k be calculated from the rate equation?
By rearranging to give:
rate /
[A]m[B]n
Must also calculate units
Increasing temp. of a reaction increases its rate.
Which part of the rate equation does this effect and why?
Effects k as doesn’t effect [A]/[B]
What are the units for a zero order reaction?
k = moldm-3s-1
What are the units for a first order reaction?
k = s-1
What are the units for a second order reaction?
k = mol-1dm3s-1
Other than reactants and k, what might appear in the rate equation?
Catalysts
What is the formula of the Arrhenius equation?
k = A-Ea/RT
What can be used to determine the value of k in the rate equation?
The Arrhenius equation
What equation do you get if you take natural logs of the Arrhenius equation?
How can this be rearranged to be in the form y = mx + c?
lnk = lnA - Ea/RT
In the form y = mx + c:
lnk = -Ea/RT x 1/T + lnA
What does T stand for in the Arrhenius equation?
What are its units?
Is it variable or constant?
Temperature
Kelvin
Variable
What does Ea stand for in the Arrhenius equation?
What are its units?
Is it variable or constant?
Activation enthalpy
Jmol-1
Variable
What does e stand for in the Arrhenius equation?
What are its units?
Is it variable or constant?
Mathmatical constant (the exponential constant)
No units
Constant…
What does A stand for in the Arrhenius equation?
What are its units?
Is it variable or constant?
The frequency factor
No units
Constant
What is the frequency factor/A in the Arrhenius equation?
Include factors such as frequency of collisions + orientation of molecules
How can you plot a graph using the Arrhenius equation experimentally?
What values can this graph be used to work out?
Can be used to calculate Ea + A
To plot, must calculate k at different temperatures
Then convert these values to lnk & 1/T to plot graph using lnk = -Ea/R x 1/T = lnA
By how much does a catalyst roughly decrease the value of Ea?
Why?
By roughly 10kJmol-1
As it significantly increases the number of collisions with energy > E<strong>a</strong> therefore increases rate
When determining the rate equation experimentally, what must be kept constant?
What will change if it is not kept constant?
Temperature
Otherwise k will change
How can you determine the rate of reaction using the initial rate method?
Graphs drawn plotting change in property over time.
Tangent drawn to t=0 giving initial rate.
Can also draw another graph with conc2 vs time to check if second order.
Once several graphs drawn for different concs of reactant used in experiment, must draw final graph with initial rate vs conc.
How can you use the progress curve method to determine the rate of reaction?
Graph showing change in conc reactant over time plotted
Series of tangents drawn at different concs, giving rate of reaction at different times
Can then use initial rate method to find order by plotting initial rate over conc.
What does a graph of initial rate over concentration look like for a zero order reaction?
Straight line
What does a graph of initial rate over concentration look like for a first order reaction?
Initial rate + conc. directly proportional
What does a graph of initial rate over concentration look like for a second order reaction?
Can either be shown as initial rate and conc2 being directly proportional (straight line) or as rate quadrupling when conc doubled (shown in pic)
How can you use the reciprocal to measure initial rate?
Done by measuring how long to produce a small, fixed amount e.g. how long for enough precipitate to form to obscure cross
Avg rate = amount of product formed to reach end point /
Reaction time for product to form
Means that avg rate ∝ 1/t. Can then plot 1/t over concs (after using several different concs in experiments)
Must keep volume constant
What is half life?
The time taken for the concentration of a reactant to half
also shown by t1/2
How can half life be used to determine the order of reaction?
Uses a graph showing conc reactant over time
Work out how long it takes for conc. reactant to half then half again, etc.
If half life constant = first order. Not constant = second/zero order
What does a graph showing conc. reactant over time look like for a zero order reaction?
Inversely proportional
What does a graph showing conc. reactant over time look like for a first order reaction?
What does a graph showing conc. reactant over time look like for a second order reaction?
Decreases more than first order
What is the rate determining step?
The slowest step of a reaction mechanism
therefore determines the rate + speed of the overall reaction
What does the rate equation tell you about the RDS?
Which compounds (in the reaction) are involves in the RDS
Can include catalysts
What does the order of reaction of each substance tell you about the RDS?
Tells you the no. moles involved in the RDS
What is an intermediate?
Chemical formed and then destroyed during the course of the reaction
