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CI Flashcards

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1
Q

What type of chemistry do many nitrogen compounds + ions play an important role in?

A

Soil chemistry

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2
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound N2O?

A

Nitrogen(I) oxide

+1

Colourless gas

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3
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO?

A

Nitrogen(iI) oxide

+2

Colourless gas

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4
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO2?

A

Nitrogen dioxide

+4

Brown gas

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5
Q

How is nitrogen (II) oxide formed from nitrogen?

A

N2 (g) + O2 (g) → 2NO (g)

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6
Q

How is nitrogen (IV) oxide formed from nitrogen (III) oxide?

What colour is the product?

A

2NO(g) + 2O2 (g) → 2NO2 (g)

Brown gas formed

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7
Q

Which nitrate do anaerobic bacteria reduce during respiration?

A

Nitrate (V)

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8
Q

What is the equation/sequence for anaerobic respiration in nitrogen-respiring bacteria?

A

NO2-(aq) → NO(g) → N2O(g) → N2 (g)

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9
Q

Why is ammonia able to act as a base?

A

Lone pair is able to accept H+ to become ammonium ion

NH3 + H+ → NH4+

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10
Q

What is nitrate (V) often known as?

A

Just nitrate

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11
Q

What is the molecular formula, bond angle, and diagram for nitrate (V) ions?

A

NO3-

120º - Triangular Planar

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12
Q

What are the properties of nitrate (V) ions?

A

Lone pairs form dative covalent bonds to O therefore increases oxidation no.

Very soluble in water

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13
Q

What is the molecular formula, bond angle, and diagram for nitrate (III) ions?

A

NO2-

120º - Triangular planar

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14
Q

What are the properties of nitrate (III) ions?

A

Very soluble in water.

Can use lone pair to form dative covalent bonds

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15
Q

What are the properties of diatomic nitrogen?

A

Very strong triple bond - low reactivity.

High bond enthalpy.

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16
Q

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?

A

They are all soluble

Must use tests involving formation of ammonia gas instead

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17
Q

What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonia?

A

-3

Trigonal pyramidal

107º due to the repulsive force of the lone pair

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18
Q

What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonium?

A

-3

Tetrahedral

109.5º

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19
Q

Describe the test for ammonium ions

A

Substance being tested warmed with added NaOH.

If ammonium present, ammonia gas formed + will turn damp red litmus blue

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20
Q

What is the equation for the test for ammonium ions?

A

NH4+(aq) + OH-(aq) → NH3 (g) + H2O(l)

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21
Q

What is the test for nitrate (V) ions?

A

Warm solution with sodium hydroxide in the presence of Devarda’s alloy (Cu, Al, Zn).

Ammonia gas formed + will turn damp red litmus blue

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22
Q

Other than using damp red litmus, how can you test for ammonia gas?

A

Using conc. HCl as when fumes mixed produces white ammonium chloride gas

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23
Q

What are the interconversions of nitrogen compounds important in maintaining?

A

The balance of nutrient ions (e.g. nitrate (V)) in the soil

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24
Q

Give the definition of a catalyst

A

Substance that speeds up the rate of reaction by providing an alternate reaction pathway with a lower Ea

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25
What is the equation for Kc?
[C]c[D]d [A]a[B]b AKA Products over Reactants
26
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.
27
If the total pressure 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
28
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
29
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)
30
What is the only factor that affects the magnitude of Kc?
Temperature
31
How can the units of Kc be found?
By substituting them into the equilibrium equation
32
What is it important to remember when calculating the units for Kc?
Must be calculated in every case (won't necessarily be the same) May have no units
33
What techniques can be used to determine equilibrium 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
34
Aside from titration, what other experimental techniques can be used to determine equilibrium constants?
Spectroscopic or calorimetric methods
35
What is stoichiometry?
Molar ratio of reactants + products in a chemical equation
36
What general equation can be used to calculate rate of reaction?
change in property (e.g conc reactant) / time taken
37
What are the units for rate of reaction usually?
moldm-3s-1 | applies if change in conc. of smth being measured
38
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
39
Complete the sentence: Quenching uses ____ _____ as conc. reactants/products determined via titration
Chemical analysis
40
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
41
Describe how colorimetry can be used to determine the concentration of an unknown sample
Make up series of standard solutions of known conc. Select filter with complimentary colour to test solutions 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 solution + read off the conc from the calibration curve
42
What is the overall order of reaction?
The sum of orders of reaction for each individual reactant
43
What is the rate equation?
Rate = k [A]^m [B]^n ``` k = rate constant [] = Concentration m = order with respect to A n = order with respect to. ```
44
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
45
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
46
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
47
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
48
If a substance is zero order, what doesn't it appear in?
The rate determining step
49
How can k be calculated from the rate equation?
By rearranging to give: rate / [A]m[B]n Must also calculate units
50
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]
51
Other than reactants and k, what might appear in the rate equation?
Catalysts
52
What is the formula of the Arrhenius equation?
k = A-Ea/RT
53
What can be used to determine the value of k in the rate equation?
The Arrhenius equation
54
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
55
What does T stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Temperature Kelvin Variable
56
What does Ea stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Activation enthalpy Jmol-1 Variable
57
What does e stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Mathematical constant (the exponential constant) No units Constant...
58
What does A stand for in the Arrhenius equation? What are its units? Is it variable or constant?
The frequency factor No units Constant
59
What is the frequency factor/A in the Arrhenius equation?
Include factors such as frequency of collisions + orientation of molecules
60
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
61
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 > Ea therefore increases rate
62
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
63
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.
64
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.
65
What does a graph of initial rate over concentration look like for a zero order reaction?
Straight line
66
What does a graph of initial rate over concentration look like for a first order reaction?
Initial rate + conc. directly proportional
67
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
68
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
69
What is half life?
The time taken for the concentration of a reactant to half also shown by t1/2
70
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
71
What does a graph showing conc. reactant over time look like for a zero order reaction?
Inversely proportional
72
What does a graph showing conc. reactant over time look like for a first order reaction?
curved downwards
73
What does a graph showing conc. reactant over time look like for a second order reaction?
steeper downwards curve than first order
74
What is the rate determining step?
The slowest step of a reaction mechanism therefore determines the rate + speed of the overall reaction
75
What does the rate equation tell you about the RDS?
Which compounds (in the reaction) are involves in the RDS Can include catalysts
76
What does the order of reaction of each substance tell you about the RDS?
Tells you the no. moles involved in the RDS
77
What is an intermediate?
Chemical formed and then destroyed during the course of the reaction
78
True of False | Nitrogen gas has a triple bond
True
79
What is the shape and bond angle of the ammonium ion?
Tetrahedral and 109.5 degrees. Despite the dative covalent bond, there are now 4 areas of electron density.
80
Nitrogen gas is very reactive, true or false?
False, the double bond requires a large amount of energy to break so nitrogen is very unreactive
81
Explain ammonia's solubility in water
Ammonia has a lone pair of electrons which can form hydrogen bonds which makes it very soluble.
82
Give the ionic equation for the formation of the ammonium ion
NH3 + H+ --> NH4+
83
Name the three common oxides of nitrogen.
NO nitrogen monoxide N2O dinitrogen monoxide NO2 nitrogen dioxide
84
Give the interconversion of ammonium and oxygen to nitrogen dioxide
NH4+ + O2 --> NO2- + 4H+ +2e- Check the balance of charges with these half equations.
85
Give the ionic equation for the release of Nitrogen gas from Nitrate (V)
2NO3- + 12H+ + 10e- --> N2 + 6H2O
86
What are the factors which affect the rate of reaction?
Surface area Catalyst Concentration of reactants (or pressure of a gas) Temperature
87
Where do products fit into the rate equation?
They don't, the rate of formation does not depend on the concentration of the products.
88
How is the rate equation linked to the equilibrium equation?
Nothing. They aren't linked
89
define the rate of reaction
the change in concentration of a reactant or product at a given time
90
what is k?
rate constant
91
what is the pattern in half lives for a zero order reaction?
half life decreases
92
what is the pattern in half lives for a first order reaction?
constant half life
93
what is the pattern in half lives for a second order reaction?
half life increases
94
what is the effect of pressure on the equilibrium constant
nothing
95
what is the effect of adding a catalyst on the equilibrium constant?
nothing
96
What produces NO
produced by combustion
97
What produces NO2
produced by the oxidation of NO
98
What produces N2O
produced by denitrifying bacteria
99
Describe the Haber process.
N2 + 3H2 2NH3 Exothermic. 400-450C, 200atm (high pressure). Iron catalyst and potassium hydroxide.
100
Which 5 things should be considered in chemical manufacture?
Cost of the process, production of co-products, production of by-products, efficiency, saving energy.

Chemistry (6 decks)

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