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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
Q

What is the equation for Kc?

A

[C]c[D]d

[A]a[B]b

AKA Products over Reactants

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26
Q

If the concentration of reactant(s) is changed, how is the position of equilibrium, Kc, and rate affected?

A

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.

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27
Q

If the total pressure of a reaction is changed, how is the position of equilibrium, Kc, and rate affected?

A

Position of equilibrium may change in order to keep ratio of reactants + products same

Kc unchanged

Rate may change

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28
Q

If the the temperature of a reaction is changed, how is the position of equilibrium, Kc, and rate affected?

A

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

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29
Q

How does a catalyst affect the position of equilibrium, Kc, and rate?

A

Position of equlibrium is unchanged

Kc unchanged

Only rate at which equilibrium reached changed, not composition (Kc)

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30
Q

What is the only factor that affects the magnitude of Kc?

A

Temperature

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31
Q

How can the units of Kc be found?

A

By substituting them into the equilibrium equation

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32
Q

What is it important to remember when calculating the units for Kc?

A

Must be calculated in every case (won’t necessarily be the same)

May have no units

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33
Q

What techniques can be used to determine equilibrium constants/how?

A

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

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34
Q

Aside from titration, what other experimental techniques can be used to determine equilibrium constants?

A

Spectroscopic or calorimetric methods

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35
Q

What is stoichiometry?

A

Molar ratio of reactants + products in a chemical equation

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36
Q

What general equation can be used to calculate rate of reaction?

A

change in property (e.g conc reactant) / time taken

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37
Q

What are the units for rate of reaction usually?

A

moldm-3s-1

applies if change in conc. of smth being measured

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38
Q

What characteristics/changes in a reaction can be monitored to identify/measure rate directly?

How can they be monitored?

A

Vol. gas evolved from a gas syringe

Mass change using a balance

pH change using a pH meter

Colour changes using a colorimeter

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39
Q

Complete the sentence:

Quenching uses ____ _____ as conc. reactants/products determined via titration

A

Chemical analysis

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40
Q

What quenching is and how it can be used to determine rate?

A

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

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41
Q

Describe how colorimetry can be used to determine the concentration of an unknown sample

A

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
Q

What is the overall order of reaction?

A

The sum of orders of reaction for each individual reactant

43
Q

What is the rate equation?

A

Rate = k [A]^m [B]^n

k = rate constant
[] = Concentration
m = order with respect to A
n = order with respect to.
44
Q

What cannot be used to determine the rate equation?

What must be used instead?

A

Cannot predict rate equation from balanced equation

Must use experimental data

45
Q

If a reactant is zero order, what is the effect of doubling the conc of the reactant on the rate of reaction?

A

No effect

rate ∝ [A]0

46
Q

If a reactant is first order, what is effect does doubling its conc have on the rate of reaction?

A

Rate doubled when conc doubled

rate ∝ [A]1

47
Q

If a reactant is second order, what happens to the rate of reaction when its conc is doubled?

A

Rate quadrupled when conc doubled

rate ∝ [A]2

48
Q

If a substance is zero order, what doesn’t it appear in?

A

The rate determining step

49
Q

How can k be calculated from the rate equation?

A

By rearranging to give:

rate /

[A]m[B]n

Must also calculate units

50
Q

Increasing temp. of a reaction increases its rate.

Which part of the rate equation does this effect and why?

A

Effects k as doesn’t effect [A]/[B]

51
Q

Other than reactants and k, what might appear in the rate equation?

A

Catalysts

52
Q

What is the formula of the Arrhenius equation?

A

k = A-Ea/RT

53
Q

What can be used to determine the value of k in the rate equation?

A

The Arrhenius equation

54
Q

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?

A

lnk = lnA - Ea/RT

In the form y = mx + c:

lnk = -Ea/RT x 1/T + lnA

55
Q

What does T stand for in the Arrhenius equation?

What are its units?

Is it variable or constant?

A

Temperature

Kelvin

Variable

56
Q

What does Ea stand for in the Arrhenius equation?

What are its units?

Is it variable or constant?

A

Activation enthalpy

Jmol-1

Variable

57
Q

What does e stand for in the Arrhenius equation?

What are its units?

Is it variable or constant?

A

Mathematical constant (the exponential constant)

No units

Constant…

58
Q

What does A stand for in the Arrhenius equation?

What are its units?

Is it variable or constant?

A

The frequency factor

No units

Constant

59
Q

What is the frequency factor/A in the Arrhenius equation?

A

Include factors such as frequency of collisions + orientation of molecules

60
Q

How can you plot a graph using the Arrhenius equation experimentally?

What values can this graph be used to work out?

A

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
Q

By how much does a catalyst roughly decrease the value of Ea?

Why?

A

By roughly 10kJmol-1

As it significantly increases the number of collisions with energy > Ea therefore increases rate

62
Q

When determining the rate equation experimentally, what must be kept constant?

What will change if it is not kept constant?

A

Temperature

Otherwise k will change

63
Q

How can you determine the rate of reaction using the initial rate method?

A

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
Q

How can you use the progress curve method to determine the rate of reaction?

A

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
Q

What does a graph of initial rate over concentration look like for a zero order reaction?

A

Straight line

66
Q

What does a graph of initial rate over concentration look like for a first order reaction?

A

Initial rate + conc. directly proportional

67
Q

What does a graph of initial rate over concentration look like for a second order reaction?

A

Can either be shown as initial rate and conc2 being directly proportional (straight line) or as rate quadrupling when conc doubled

68
Q

How can you use the reciprocal to measure initial rate?

A

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
Q

What is half life?

A

The time taken for the concentration of a reactant to half

also shown by t1/2

70
Q

How can half life be used to determine the order of reaction?

A

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
Q

What does a graph showing conc. reactant over time look like for a zero order reaction?

A

Inversely proportional

72
Q

What does a graph showing conc. reactant over time look like for a first order reaction?

A

curved downwards

73
Q

What does a graph showing conc. reactant over time look like for a second order reaction?

A

steeper downwards curve than first order

74
Q

What is the rate determining step?

A

The slowest step of a reaction mechanism

therefore determines the rate + speed of the overall reaction

75
Q

What does the rate equation tell you about the RDS?

A

Which compounds (in the reaction) are involves in the RDS

Can include catalysts

76
Q

What does the order of reaction of each substance tell you about the RDS?

A

Tells you the no. moles involved in the RDS

77
Q

What is an intermediate?

A

Chemical formed and then destroyed during the course of the reaction

78
Q

True of False

Nitrogen gas has a triple bond

A

True

79
Q

What is the shape and bond angle of the ammonium ion?

A

Tetrahedral and 109.5 degrees. Despite the dative covalent bond, there are now 4 areas of electron density.

80
Q

Nitrogen gas is very reactive, true or false?

A

False, the double bond requires a large amount of energy to break so nitrogen is very unreactive

81
Q

Explain ammonia’s solubility in water

A

Ammonia has a lone pair of electrons which can form hydrogen bonds which makes it very soluble.

82
Q

Give the ionic equation for the formation of the ammonium ion

A

NH3 + H+ –> NH4+

83
Q

Name the three common oxides of nitrogen.

A

NO nitrogen monoxide
N2O dinitrogen monoxide
NO2 nitrogen dioxide

84
Q

Give the interconversion of ammonium and oxygen to nitrogen dioxide

A

NH4+ + O2 –> NO2- + 4H+ +2e-

Check the balance of charges with these half equations.

85
Q

Give the ionic equation for the release of Nitrogen gas from Nitrate (V)

A

2NO3- + 12H+ + 10e- –> N2 + 6H2O

86
Q

What are the factors which affect the rate of reaction?

A

Surface area
Catalyst
Concentration of reactants (or pressure of a gas)
Temperature

87
Q

Where do products fit into the rate equation?

A

They don’t, the rate of formation does not depend on the concentration of the products.

88
Q

How is the rate equation linked to the equilibrium equation?

A

Nothing. They aren’t linked

89
Q

define the rate of reaction

A

the change in concentration of a reactant or product at a given time

90
Q

what is k?

A

rate constant

91
Q

what is the pattern in half lives for a zero order reaction?

A

half life decreases

92
Q

what is the pattern in half lives for a first order reaction?

A

constant half life

93
Q

what is the pattern in half lives for a second order reaction?

A

half life increases

94
Q

what is the effect of pressure on the equilibrium constant

A

nothing

95
Q

what is the effect of adding a catalyst on the equilibrium constant?

A

nothing

96
Q

What produces NO

A

produced by combustion

97
Q

What produces NO2

A

produced by the oxidation of NO

98
Q

What produces N2O

A

produced by denitrifying bacteria

99
Q

Describe the Haber process.

A

N2 + 3H2 2NH3
Exothermic. 400-450C, 200atm (high pressure).
Iron catalyst and potassium hydroxide.

100
Q

Which 5 things should be considered in chemical manufacture?

A

Cost of the process, production of co-products, production of by-products, efficiency, saving energy.

Chemistry (6 decks)

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