1
Q
Endothermic reactions
A
1) absorb thermal energy (gets colder)
2) thermal energy»_space;> chemical energy
3) delta H = positive
2
Q
Exothermic reactions
A
1) release thermal energy (gets hotter)
2) chemical energy»_space;> thermal energy
3) delta H = negative
3
Q
Energy profile diagrams
A
- Vertical axis: enthalpy (kJ/mol or KJ)
- horizontal axis: progress of reaction
- exothermic: reactants higher than products
- endothermic: reactants below products
4
Q
Complete combustions
A
fuel + 02 (g)»_space;> CO2(g) + H2O(l)
- product is CO2(g)
- more oxygen used overall
5
Q
incomplete combustion
A
- products: carbon monoxide (CO) or carbon particulates (C)
- less oxygen used overall
6
Q
Thermochemical Equations
A
MUST have states and delta H value
7
Q
FORMULA to convert between mass and moles
A
n = m/M
8
Q
FORMULA to find energy released by a fuel
A
q = delta H x n
with help from data book
9
Q
different FORMULAS of delta H
A
1) if in kJ/mol: delta H = q/n
2) if in kJ/g: delta H = q/m
3) if in kJ/mL: delta H = q/v
10
Q
FORMULA of density
A
d = m/v
- volume can be in both ml & L
11
Q
FORMULA to find energy absorbed by water
A
q = MCAT
- given specific heat capacity of water is 4.18 J/g/K
12
Q
how to find delta H experimentally??
A
1) find temp change of water
- use q = MCAT formula
2) find change of mass of fuel
- use n = m/M
3) then calculate delta H
- use delta H = q/n
13
Q
FORMULA of percentage efficiency of a ‘fuel’
A
% eff = actual / theoretical x 100
AKA
% eff = output / input x 100
14
Q
what are systematic errors?
A
links to ACCURACY
(how close a measurement is to the true value)
15
Q
what are random errors?
A
link to PRECUSION
(how close a measurement is to each other)
16
Q
WAYS to minimise heat loss (in the experiment)
A
1) add a lid
2) bring flame closer
3) insulate the sides of the beaker
4) place heat shields on sides
17
Q
stoichiometric ratios
A
- ALWAYS in moles
unknown / known
18
Q
what are SLC conditions?
A
temperature @ 25 degrees celsius
pressure @ 100kpa
redox: ph @ 0
19
Q
universal gas law
A
PV = nRT
- not tested in chem 3/4
20
Q
FOMULA for volume occupied by gas IN SLC CONDITIONS
A
n = V / Vm
21
Q
what is the molar volume (Vm) of gases?
A
24.8L/mol
22
Q
volume to volume stoich:
CONDITIONS + how
A
1) temperature is constant
2) pressure is constant
3) all substances must be gas
- just multiply ratio with volume
23
Q
how to find limiting reagent?
A
1) find moles of both reactants
2) divide both by their respective coefficient
3) the lower one = limiting reagent
24
Q
how to find how much excess reagent is left after all of limiting reagent is used up
A
1) find amount of excess used
2) subtract that value from how much there is left
initial - used
25
features of a calorimeter
- in 3/4 a SOLUTION calorimeter is tested
- the sides are insulated to minimise heat loss, so most of the energy goes straight to the water
! heat is transferred directly to water
26
purpose of stirrer
to evenly distribute heat
+
ensure there is a constant temperature
27
purpose of glass bulb
initially separates the reactants and prevents reaction to occur
28
what is a calorie
IT is the energy required to heat up 1g of water by 1 degree celcius
- there are 4.18 joules in ONE calorie
29
DEF: calibration factor
aka: CF
IT is a measure of how much energy is required to change the temperature of a substance in the calorimeter by 1 degree celcius
30
FORMULA of calculating the CF
CF = energy inputted (E) / the temperature change observed (AT)
31
DEF: electrical calibration
- when the calorimeter can be calibrated using the electric heater
32
FORMULA to find the electrical calibration factor CF
CF = E / AT
E = VIT
v: voltage (volts(v))
I: current (amps)
T: time (seconds)
33
DEF: chemical calibration
- the calorimeter can be calibrated chemically by combusting an organic molecule with a known change in enthalpy value
34
FORMULA for chemical calibration factor CF
CF = E / deltaT
E = delta H x n (if in kj/mol)
E = delta H x m (if in kj/grams)
35
FORMULA of concentration
c = n / V
36
temperature - time graphs
37
what is a renewable fuel? (DEF)
a fuel that can be replenished by natural processes within a relativly short period of time.
38
How is coal formed
from the fossilisation of dead? plant and animal matter
39
crude oil
- non renewable
- consists of a nixture of hydrocarbons, namely alkanes, ranging from 1 to 30 carbons.
- carbon is sperated by fractional distilation
40
WHAT is natural gas
- about 95% CH4 & 5% CO2
- a gas found underground
- non-renewable
- can be found in coal sam gas deposits found in coal mines
41
WHAT is biogas
- renewable
- produced from biomass/biowaste
42
how is biogas produced
- formed from the anerobic breakdown of organic matter by bacteria
43
Bioethanol
- renewable
- formed from the fermentation of glucose with the help of yeast
44
Fermentation equation
C6H12O6 (aq) -> 2C2H5OH(aq) + 2CO2
45
Distillation
- a process of sperating a liquid mixture by boiling the mixture.
- mixture is heated tp the target temperature
- that temperature is between two substances boiling points
46
distillate
the substance that is evaporated and condensed back back down in distillation
47
purpose of distillation
- increases efficiency upon combustion of ethanol as less water is present
-
48
what biodiesel
- renewable
- made up of fatty acid methyl ester
49
biodiesal - formation
- from plant and animal fats/oils
- transesterification
50
partially oxidised
A fuel that already contains oxygen in the molecular formula (eg. methanol = CH3OH)
THUS HEAT OF COMBUSTION WOULD BE LOWER bc partially oxidised = 'partially burnt'
51
Carbon neutrality
when the carbon dioxide released when using the fuel is previously offset during the production of fuel.
52
reasons for carbon neutrality
the production of glucose via photosynthesis
6CO2(g) + 6H2O(l) -> C6H12O6(aq) + 6O2(l)
-> catalyst: UV light + chlorophyll
53
Reasons AGAINST carbon neutrality
other factors which contribute to carbon emmissions during the production of fuel:
- farming equipment
- transportation vehicles
54
carbohydrates
store/provide energy (quick energy) and fiber (remove waste)
55
Fats/oils
store/provide energy (slow energy), shock absorbtion/insulation, and storage of fat-soluble vitamins
56
proteins
helps with growth/ repair of cells, helps with immunity and transport of molecules,a nd enzymes
57
______________
___________________
58
Redox reaction
- the transfer of electrons
- must occur in pairs
59
redox half-equations
- the two half equations cannot occur bu themselves. MUST OCCUR TOGETHER
- one gives away electrons and the other takes in electrons
60
OIL RIG
oxidation is loss
reduction is gain
61
oxidation number
- the hypothetical charge of an atom if the bonding is purely ionic
- according to the OCTET rule, atoms generally want eight electrons in it's outer shell
62
oxidising agent
AKA (oxident)
- causes the oxidation of another substance
- UNDERGOES reduction
63
reducing agent
AKA (reducatant)
- causes the reduction to another substance
- UNDERGOES oxidation
64
congugate redox pairs (x^+/x)
oxident/reductant
65
balancing redoox equations in ACIDIC conditions
KOHES
66
balancing redoox equations in BASIC conditions
1)KOHES
2) add OH- on both sides
3) simplify/cancel out
67
net ionic equation
a balanced full equation with spectator ions omitted
68
spectator ions
(ions which do not change states)
- compounds which is present but do not participate in the reaction
69
where is the strongest oxident on ELECTROCHEMICAL series?
top LEFT
70
where is the strongest reductant on ELECTROCHEMICAL series?
bottom RIGHT
71
spontaneous slopes
negative slopes
IMAGINE a ball being able to roll down BY ITSELF without help
FROM THE LEFT
72
what happens if there are multiple oxidents and reductants?
only the strongest oxidents will react with the strongest reductant
73
ENERGY CONVERSATIONS:
for direct contact spontaneous redox equation
chemical TO thermal
74
ENERGY CONVERSATIONS:
for indirect contact spontaneous redox equation
chemical TO electrical
75
why may a reaction not occur for some metals
- rate of reaction too slow
THE electrochemical series does not predict the state of reaction
the strenghts of oxident/reductant DOES NOT affect the rate of reaction
76
Galvanic cell
an electrochemical cell that converts the chemical energy of spontaneous redox reactions into electrical energy
- reactants ARE NOT in direct contact
INDIRECT redox reaction
77
3 main part/components of a galvanic cell
- 2 x half cells = i galvanic cells
- external circuit (load + wire)
- salt bridge (internal circuts)
78
electrode
electrical conductors, which carry electrons to/from the non-metallic part in ana eledtrolyte
- allows movement of ELECTRONS
79
electrolyte
contains ions which can conduct electricity due to the movement of ions
- allows movement of IONS
FUNCTION: to complete the circuit by allowing the flow of charges particles through the cell
80
is a gas is a product, is a gas tube required?
NO
81
Inert electrode
platinum (Pt) & graphite (c)
82
How do you know what reaction happens at each electrode
AO -
anode = oxidation (-)
RC +
reduction = cathode (+)
83
electron flow in galvanic
anode TO cathode
84
internal circut
- used to balance the build -up of charge
PROPERTIES:
- inert (does not react)
- soluble (does not doem a percipitate)
MOST COMMON: KNO3(aq)
85
FORMULA: electromotive force (EMF)
E(oxident) - E(reductant) = EMF
top - bottom
CONDITIONS: slc + 1.0M
86
CHANGES is size/mass of electrodes
at cathode mass INCREASES
at anode, mass DECREASES
87
Changes in PH
(H+)
in OXIDATION: if concentration of H+ ions increase = more acidic = PH decrease
in REDUCTION: H+ ions increases = less basic = PH increases
88
Changes in PH
(OH -)
in OXIDATION: concentration of ions increase = more basic = PH increase
in REDUCTION
concentraton of ions decrease = less basic = PH decrease
89
Gases
if a gass is a product , Bubbles are formed in reaction
if gass reactant, use a gas tube
90
colour
in OXIDATION:
- product = NI 2+
SO ion concentration increases = colour increases
in REDUCTION:
- ions are being used up = colour decreases
"more/less intesly... [colour]"
LOOK AT DATA BOOK
91
Fuel cell has:
- has a shared electrolyte
- no salt bridge
- continous suppply of reactants
92
define fuel cell:
a galvanic cell that produces electrical energy from chemical energy, and is characterised by a continuous supply of reactants
- uses FUEL as a reactant
93
Fuel cell: overall reaction
combustion reaction
94
Fuel cell: energy converstations
chemical TO electrical
95
Fuel cell: electrolyte
- acts similar to salt bridge, balances the build up of charge
96
Fuel cell: electrolyte movement
cations -> cathode
anions -> anodes
97
Fuel cell : oxygen + fuel
O: ALWAYS undergoes REDUCTION
fuel: always undergoes oxidation
98
balancing half-equations for carbon containing fuels
- unless specified, assume carbon containing fuel oxidises into CO2(g)
- use KOHES to balance
99
Properties of fuel cell ELECTRODES acronym
PICCY
100
Porous electrode
1) ensures that the gaseous, fuel/oxygen can come into contact with the eledtrode
2) increases surface area = increased rate of reaction
101
inert electrode
electrode is unreactive, thus ensures that no other reaction occurs
102
catalyst electrode
increases rate of reaction
103
electrode conducts electricity
ensures that electrons can flow through the external circut
104
energy efficiency and pollution in a fuel cell (vs power stations)
1. fuel cell has direct energy conversion (chemical TO electrical)
2. meaning less energy is wasted and thus is more efficient
3. therefore, in comparison to a power station, less fuel is required to release tje same amount of energy . Also, therefore, less polutants and greenhouse gases would be produced
105
green chemistry principle FOR fuel cells
1) design for energy efficiency
2) use of renewable feedstocks
106
ADVANTAGES of fuel cells
1) more energy efficient, less fuel required
2) quiet
3) low start/stop time
107
DISADVANTAGES of fuel cell
1) expensive
-
2) hydrogen storage/safety
108
what is both inert and a catalyst in fuel cells
platinum
109
is there a difference between the overall ewation in acidic & basic conditions?
NO, they are the exact same.
- the charge is also the same 1.23v EMF
110
PRIMARY cell
a galvanic cell which produces electrical energy and CANNOT be recharged
111
PRIMARY cells: electrolyte purpose
- to allow for the movement of ions to balance charges around the electrodes
(acts similar to the salt bridge)
- provides the internal circuit in the cell
112
what is the most common metal used in batteries
LITHIUM:
- it is the stronger reductant in the electrochemical series
- THUS it results in a higher EMF production
113
primary vs fuel cells: type of reaction
both are sopntaneous
114
primary vs fuel cells: reactants
primary: are stored in each half-cell
fuel: there is a continuous supplu of reactants
115
primary vs fuel cells: electrodes
P: conduct electricity
F: PICCY
116
primary vs fuel cells: reactivity of electrodes
P: may participate in the chemical reaction
F: will not participate in the chemical reaction
117
primary vs fuel cells: price
P: cheap
F: expensive
118
primary vs fuel cells: electrolyte
P: each half cell has its own electrolyte BUT they may also share an electrolyte
F: shared electrolyte
119
primary vs fuel cells: energy efficency
BOTH hsve high energy efficiency because they both have direct energy conversions from chemical to electrical
120
electric charge
the amount of charged particles (e.g electrons) that are present
- denoted by: Q
- si units: columbs (C)
121
electric current
the rate of flow of charged particles per second
- denoted by: I
- si units: amps (A)
122
electrical charge FORMULA
Q = IT
123
Faraday's first law of electrochemistry
Q is DIRECTY proportional to mass
- eg. as MORE electrical charge passes throught he cell, the amount of substance that react/are produced also INCREASES
124
elementary charge
the charge carried by the elementary particle (electrons)
value: -/160 x 10 ^-19
125
faraday's constant
the quantity of charge carried by one more of electrons
- 96500 C / mol
126
FORMULA linking electric charge and moles of electrons
n(e^-) = Q / F
127
Farafay's second law of electrochemistry
TO consider the stoichiometric ratio between n(e^-) : n(metals)
128
STEPS to derive a charge of a ion
1) find n(metal) by n(metal) = m/Mr
2) find n(e^-) by Q/F
3) find stoichometric ration by divinding the smallest number present
129
intramolecular bonding
within molecules
130
TYPES of intramolecular bonds
ionic bonding
covalent bonding
metallinc bonding
131
intermolecular bonding
between molecules
132
TYPES of intermolecular bonds
1. dispersion forces
2. dipole - dipole
3. hydrogen bonds
133
what are dispersion forces?
Dispersion forces are weak attractions caused by temporary electron shifts in molecules.
134
what are dipole-dipole forces?
Dipole-dipole forces are attractions between polar molecules due to their partial positive and negative charges.
They are stronger than dispersion forces but weaker than hydrogen bonds.
135
what are hyrdogen bonds?
Hydrogen bonds are strong dipole-dipole attractions between molecules containing H bonded to N, O, or F.
They are stronger than regular dipole-dipole forces but weaker than covalent bonds.
136
differences within fuel vs galvanic experiments
1) continuous supply vs fixed amount of reactants
2) electrodes act as catalyst and inert vs electrodes may be consumed part of reaction
3) more energy efficient vs efficiency may vary and typically decrese as cell discharges
137
possible random errors
1) enviromental conditions: changes in temp, humidity or air pressure can affect the experiement -> leads to flunctuation in reaction rates and measuremnts
2) variations in readings of measurements: MAY be due to human error or equipment sensitivity. EG. slight changes in voltages reading
138
possible systematic errors
1) equipment may not be properly calibrated (voltmeters/thermometers/PHmeters) or innacurate timers = lead to consistent deviations in measuremnts
2) worn or improperly prepared elctrodes = consistent errors in measurements = affecting the cell's performance
139
sample resopnse for fuel cell vs conbustion
direct energy conversion from chemical →
electrical energy.
LESS energy loss, MORE energy efficient.
LESS fuel is required in a fuel cell
to produce the SAME amount of
energy.
Less overall CO2 emissions overall.
140
CHEM
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