Download Topic guide 5.2: Studying the feasibility of reactions

Unit 5: Chemistry for Applied Biologists
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Studying the feasibility
of reactions
Chemical reactions can be described as feasible if they occur without an
external source of energy. In this topic you will learn about the use of Gibbs
energy changes as a measure of feasibility for all reactions, as well as the
use of electrode potential data in the case of redox reactions. In the case of
biochemical systems, unfeasible reactions may still occur if they are coupled
to reactions that are feasible.
On successful completion of this topic you will:
•• be able to relate the feasibility of reactions to thermodynamic quantities
(LO1).
To achieve a Pass in this unit you need to show that you can:
•• use values of thermodynamic state functions to assess the feasibility of
reactions (2.1)
•• write oxidation and reduction half-equations for given reactions (2.2)
•• categorise reactions as oxidation/reduction (redox) on the basis of
oxidation numbers (2.3)
•• justify the feasibility of redox reactions in terms of standard reduction
potentials (2.4).
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Unit 5: Chemistry for Applied Biologists
1 Thermodynamic quantities
Key terms
Feasible: A reaction that is
thermodynamically favourable.
A feasible reaction will occur
spontaneously.
Entropy: A measure of the disorder
of a system.
Spontaneous: A reaction that can
occur without an input of energy. The
rate of a spontaneous reaction may,
however, be too small to allow it to
be observed.
In Topic guide 5.1 you met the thermodynamic quantity enthalpy; it is obvious
that enthalpy changes are not, by themselves, a measure of feasibility since
both exothermic and endothermic reactions can be feasible depending on the
conditions.
Entropy
The key to evaluating feasibility is the idea of entropy. Entropy (symbol S) is
a thermodynamic quantity that measures the disorder of a chemical system.
Molecules that are free to move (as in the case of gases) or that are moving rapidly
can be thought of as possessing high levels of entropy (are highly disordered).
The second law of thermodynamics
The importance of entropy (or rather of entropy changes) to the feasibility of a
reaction stems from the second law of thermodynamics, which states:
‘in any spontaneous process, the total entropy of the universe will increase’.
In any chemical process, the total entropy change will be composed of a
contribution from the system (the reacting chemicals) and the surroundings (the
rest of the universe which is not part of the system but which can exchange heat
with the system).
The entropy change of the system takes into account the change in disorder of the
particles involved in the reaction; the entropy change of the surroundings takes
into account the change in disorder due to the heat which is exchanged with the
system.
This can be written:
ΔStotal = ΔSsystem + ΔSsurroundings
From the second law of thermodynamics it follows that for a reaction to be
feasible then ΔStotal must be positive.
Calculating entropy
Calculation of ΔSsystem
Tables of data provide information about the standard molar entropy of a range
of substances. This is the entropy of a mole of that substance measured under
standard conditions (see Topic guide 5.1).
ΔSƟsystem can be calculated from these data:
ΔSƟsystem =
ΣS
Ɵ
products
–
ΣS
Ɵ
reactants
Calculation of ΔSsurroundings
As ΔSsurroundings is connected to the heat exchanged with the surroundings, it can be
calculated from the enthalpy change, ΔH, of a reaction.
ΔH can be measured experimentally, or calculated using values of standard
enthalpy changes of formation of substances (see Topic guide 5.1).
5.2: Studying the feasibility of reactions
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Unit 5: Chemistry for Applied Biologists
ΔSsurroundings can then be calculated using the following equation, as long as the
temperature remains constant during the process:
ΔH
(ΔH measured in joules, T measured in Kelvin)
ΔSsurroundings = –
T
The values of ΔSsurroundings and ΔS system can be combined to give a value of ΔStotal and
thus allow the feasibility of a reaction to be deduced.
Take it further
Thermodynamic data, such as molar entropy values or enthalpy change data, can be found in
online databases such as the NIST databook http://webbook.nist.gov/chemistry/.
Activity
1 The vaporisation of water is represented by the following equation:
H2O(l) ➝ H2O(g)
a Use tables of thermodynamic data to find or calculate a value for ΔSƟsystem. Comment on the
sign of this quantity. Does it suggest that the system is becoming more or less disordered?
b Find a value of ΔHƟ for this process and use it to calculate ΔSƟsurroundings at 298 K.
c Combine your answers to (a) and (b) and calculate a value for ΔStotal at 298 K. What can you
say about the feasibility of the process?
d If the temperature is raised, at what value would you expect the reaction to become
feasible? Test your prediction by calculating a value for ΔSsurroundings at this temperature and
hence ΔStotal at the same temperature (assume that the value of ΔSsystem does not change
significantly).
2 The oxidation of ethanol to ethanoic acid under aerobic conditions can be represented by the
equation:
C2H5OH(l) + O2(g) ➝ CH3COOH(l) + H2O(l)
a Use tables of thermodynamic data to find values of the enthalpy of formation for all of the
compounds involved in the reaction. Hence calculate a value for the enthalpy change of
reaction, ΔHƟ.
b Use the value of ΔHƟ to calculate a value for ΔSƟsurroundings at 298 K (Hint: remember to
convert ΔHƟ into joules).
c Use tables of thermodynamic data to find values of SƟ for all the substances in this equation.
Hence calculate a value for ΔSƟsystem.
d Use your answers from (b) and (c) to calculate a value for ΔSƟtotal at 298 K.
e Comment on the feasibility of this process. What assumptions have you made about the
states of the reacting substances? Is this justified?
Gibbs energy
A much more convenient approach to evaluating the feasibility of chemical
reactions – and in particular biochemical reactions – is to use a thermodynamic
quantity known as the Gibbs energy (sometimes called the Gibbs free energy, G).
Link
The meaning of the Ɵ superscript was
explained in Topic guide 5.1.
This has the same units as ΔH (kJ mol–1) but also takes into account the entropy
change of the system. It is defined by the following equation:
ΔGƟ = ΔHƟ – T ΔSƟsystem
It can also be shown that ΔG is then related to the value of ΔStotal for a reaction:
ΔGƟ = −T ΔSƟtotal
So, from the second law of thermodynamics:
ΔGƟ must be negative in order for a reaction to be feasible.
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Values of ΔGƟ
Values of ΔGƟ for biochemical reactions are widely quoted in reference books or
websites. Alternatively, ΔGƟ can be calculated from thermodynamic data in the
following ways:
•• from values of ΔHƟ and ΔSƟsystem using the equation: ΔGƟ = ΔHƟ – T ΔSƟsystem
•• from values of ΔGƟformation using the equation:
ΔGƟsystem =
Σ ΔG
Ɵ
formation
(products) –
Σ ΔG
Ɵ
formation
(reactants)
ΔGƟ gives much more information than simply the feasibility of the reaction; its
magnitude also defines the amount of ‘useful work’ that can be extracted from a
chemical process (useful work in this case can mean electrical energy or energy
used to drive other reactions – anything other than the work used to cause a
system to expand).
These are very important data to know about a biochemical reaction which may
be used to drive other vital cell processes, such as active transport or biosynthesis.
Of course ΔGƟ values only apply to reactions occurring under standard conditions;
ΔG values may then be quoted if a reaction is occurring under non-standard
conditions.
Take it further
Thermodynamic tables of data are widely found in chemical reference books or online at sites such
as http://www2.ucdsb.on.ca/tiss/stretton/database/organic_thermo.htm.
Key terms
Exergonic: A reaction accompanied
by a negative Gibbs energy change
(and hence from which useful work
may be produced).
Endergonic: A reaction accompanied
by a positive Gibbs energy change
and hence which are not, by
themselves, feasible.
Equilibrium (chemical): A situation
in which the proportion of reactants
and products remains constant
because the rates of forward and
backward reactions are equal.
The sign of ΔGƟ (or ΔG if the conditions are non-standard) is very important, as you
will see in the following sections, and the terms exergonic and endergonic are
used to describe the sign of the Gibbs energy change.
Activity
Find, or calculate from appropriate data, values of ΔGƟ for the following processes (remember
that ΔGƟ can be calculated from the ΔGƟformation values for the products and reactants):
1 The combustion of methane: CH4 (g) + 2O2(g) ➝ CO2(g) + 2H2O(g)
2 Complete oxidation of glucose: C6H12O6(s) + 6O2(g) ➝ 6CO2(g) + 6H2O(l)
3 Phosphorylation of ADP to ATP: ADP + Pi + H+ ➝ ATP + H2O.
ΔG and equilibrium
For a given equation, it is important to realise that the value of ΔGƟ refers to a
reaction that goes to completion.
Clearly many reactions – including the majority of biochemical processes – are
regarded as reversible processes that will reach equilibrium in a closed system.
How can a reaction be reversible if only one direction is feasible? Well, we know
that the Gibbs energy of reactants and products can be calculated, but it is also
possible to calculate Gibbs energies of equilibrium mixtures with various ratios of
products to reactants. These are shown graphically in Figure 5.2.1.
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Figure 5.2.1: The
relative values of the
Gibbs energies (G) of
products and reactants
determines the position
of equilibrium which
will be reached.
G
G
G
∆G –ve
100%
reactant
100%
product
Equilibrium
favours
products
∆G +ve
100%
reactant
Equilibrium
favours
reactants
100%
product
∆G = 0
100%
reactant
100%
product
Equilibrium favours
neither reactants
nor products
Notice that in each of these cases there is a fixed proportion of products to
reactants which gives a minimum value of Gibbs energy. The formation of this
equilibrium mixture from either reactants or products will be feasible, since in
both cases the Gibbs energy decreases during the reaction.
The sign of ΔGƟ allows us to make predictions about the proportion of products
which will be formed at equilibrium:
1if ΔGƟ is negative, the proportion of products present will be large (the
equilibrium position favours the right-hand side)
2if ΔGƟ is positive, the proportion of products present will be small (the
equilibrium position favours the left-hand side)
3if ΔGƟ is zero, there will be equal proportions of products and reactants.
Technically, all reactions result in an equilibrium mixture being formed, but if ΔGƟ
is more negative than about −40 kJ mol–1 then the reaction is regarded as having
gone to completion. If ΔGƟ is more positive than about +40 kJ mol–1 the reaction is
regarded as not having occurred at all.
Portfolio activity (2.1)
Choose a simple biological process involving substances for which thermodynamic data is readily
available. A suitable example could be the hydrolysis of urea:
CO(NH2)2 + H2O ➝ CO2 + 2NH3
Use tables of thermodynamic data to investigate the feasibility of this reaction. In your answer:
•• use suitable data to calculate values of ΔHƟformation and ΔSƟsystem
•• calculate a value for ΔSƟtotal at 298 K
•• calculate a value for ΔGƟ
•• explain what you can deduce from your calculations about the feasibility of the process at
298 K.
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Unit 5: Chemistry for Applied Biologists
2 Oxidation and reduction
Many biochemical reactions are described as redox reactions.
These reactions generally involve the transfer of electrons between biochemical
molecules.
Half-equations
It is often helpful to split up the overall reaction into half-equations, which
show the processes of reduction and oxidation separately. Unlike full balanced
equations, half-equations clearly show the way in which electrons are transferred
in each process.
To take a simple, non-biological example, zinc displaces copper from solutions of
copper(II) salts.
Zn(s) + Cu2+(aq) ➝ Zn2+(aq) + Cu(s)
The two half-equations are:
Key terms
Redox reaction: A reaction in which
both oxidation and reduction occur
simultaneously.
NADH and NAD+: These are the
reduced and oxidised forms of the
molecule nicotinamide adenine
dinucleotide. They play an important
role in enabling electron transfer
to take place during biochemical
reactions.
Reduction: Cu2+(aq) + 2e− ➝ Cu(s)
Oxidation:Zn(s) ➝ Zn2+(aq) + 2e−
Biological examples of redox reactions are a little more complex. For example,
during anaerobic respiration, pyruvate is reduced to lactate by NADH (using the
enzyme lactate dehydrogenase).
pyruvate + NADH + H+ ⇌ lactate + NAD+
The two half-equations are:
Reduction: pyruvate + 2H+ + 2e− ➝ lactate
Oxidation:NADH ➝ NAD+ + H+ + 2e−
Reduction and oxidation in terms of electron transfer
From the equations above it is evident that:
1 reduction involves the gain of electrons
2 oxidation involves the loss of electrons
3 zinc and NADH act as reducing agents, and in the process they are oxidised.
Notice that the overall equation can be obtained from the half-equations by
simply adding the two half-equations together, so long as the number of electrons
is identical, which enables them to be cancelled out, as shown in the following
example:
in the case of the Zn / Cu2+ system
Cu2+(aq) + 2e- ➝ Cu(s)
Zn(s) ➝ Zn2+(aq) + 2eCu2+(aq) + Zn(s) ➝ Cu(s) + Zn2+(aq)
5.2: Studying the feasibility of reactions
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Unit 5: Chemistry for Applied Biologists
Activity
1 Copper metal can oxidise silver ions to metallic silver. The two half-equations are:
Cu(s) ➝ Cu2+(aq) + 2e−
Ag+(aq) + e− ➝ Ag(s)
Write an overall equation for this process. (Hint: in order to be able to combine the equations
together, the number of electrons must balance. To achieve this you will need to multiply the
numbers in one of the equations by two before combining them.)
2 Oxygen can oxidise iron metal to Fe2+ ions in the presence of water. The two half-equations for
the reaction are:
Fe(s) ➝ Fe2+ + 2e−
½O2(g) + H2O(l) + 2e− ➝ 2OH−
Combine these two half-equations together to produce an overall equation for this process.
3 Oxygen can also oxidise NADH during the electron-transport chain that occurs in oxidative
phosphorylation. The two half-equations are:
NADH ➝ NAD+ + H+ + 2e−
½O2 + 2H+ + 2e− ➝ H2O
Combine these half-equations together to produce an overall equation for this process.
Portfolio activity (2.2)
Choose some simple chemical redox reactions. Suitable examples could include:
•• displacement reactions involving halogens, such as the reactions between chlorine and
bromide ions
•• reactions between reactive metals and acids (represented by H+ ions).
In your answer you should:
•• write the overall equation for the reaction
•• write down two half-equations which combine to produce the overall equation
•• classify each half-equation as reduction or oxidation, explaining your answer.
Reduction and oxidation in terms of oxidation number
If half-equations are not written out, it can be difficult to analyse an equation for a
process to deduce what is being oxidised and what is being reduced.
Chemists use a strategy that involves assigning an oxidation number (sometimes
called an oxidation state) to each atom involved in the reaction.
Oxidation numbers describe the number of electrons lost, gained or shared by an
atom as a result of forming bonds.
The oxidation number of an uncombined element is always zero (even for
elements that exist as molecules such as O2).
Rules for assigning oxidation number
Oxidation numbers are assigned to individual atoms in compounds using a set of
rules. Although these are easy to apply to simple molecules and ionic compounds,
they can become very difficult to use with molecules based on chains and rings of
carbon atoms.
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Unit 5: Chemistry for Applied Biologists
•• The total oxidation number of all the atoms in a neutral compound is zero.
•• The oxidation number of an ion is equal to the charge on the ion.
–Examples: a sodium ion has the formula Na+; the oxidation number of
sodium is +1.
The nitrate ion has the formula NO3−; the total oxidation number of all the
atoms in the ion adds up to −1.
•• Some atoms have oxidation numbers that are almost always constant when
they are present in compounds:
– oxygen is −2 (except in peroxides)
– hydrogen is +1 (except in metal hydrides)
– fluorine is −1
– chlorine is −1 (except when bonded to oxygen or fluorine).
Take it further
You can read about the rules for assigning oxidation numbers and how to apply them to
compounds in most level 3 chemistry textbooks, or online at sites such as:
http://www.chemguide.co.uk/inorganic/redox/oxidnstates.html.
Activity
Use the rules for assigning oxidation numbers to write down the oxidation number of:
a Mg in MgCl2
b N in NO2
c N in N2O5 (hint: the oxidation number applies to a single atom of N)
d P in PO43– (hint: remember that the total oxidation number equals the charge on the ion)
e O in hydrogen peroxide, H2O2 (hint: look back at the exceptions in the list).
Identifying redox reactions using oxidation numbers
1An atom has been oxidised if its oxidation number becomes more positive (or
less negative).
2
n atom has been reduced if its oxidation number becomes less positive (or
A
more negative).
If no changes in oxidation numbers occur during the reaction, then it cannot be
classified as a redox process.
For example, the reaction for the decomposition of hydrogen peroxide in the
presence of catalase is:
2H2O2 oxidation numbers: ➝ O2+ 2H2O
+1 −1
0
+1 −2
So during the reaction, the oxygen atoms have been both oxidised (−1 to 0) and
reduced (−1 to −2).
Activity
Write down the oxidation numbers of the atoms in each of the reactants and products in these
equations for redox reactions:
1 Mg + 2HCl ➝ MgCl2 + H2
2 2H2O + 2F2 ➝ 4HF + O2
3 MnO4− + 8H+ + 5Fe2+ ➝ Mn2+ + 5Fe3+ + 4H2O
5.2: Studying the feasibility of reactions
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Unit 5: Chemistry for Applied Biologists
Portfolio activity (2.3)
Nitrogen atoms display a wide range of oxidation numbers in compounds.
Use the following reactions to explain how oxidation numbers can be used to help decide if a
given reaction is a redox process.
1 C + 4HNO3 ➝ CO2 + 4NO2 + 2H2O
2 NH4+ + CO32− ➝ NH3 + HCO3−
3 5NO2− + 2MnO4− + 6H+ ➝ 5NO3− + 2Mn2+ + 3H2O
In your answer you should:
•• write down the oxidation number of the different atoms in each reactant and product for the
three equations
•• explain whether a redox reaction has occurred
•• identify the reducing and oxidising agent in each reaction.
3 Standard reduction potentials
Electrochemical cells
Chemists have long studied redox reactions by constructing electrochemical cells
in which the two half-reactions occur in different parts of the electrochemical cell.
Reduction occurs at one electrode and oxidation at the other and electrons flow
between the two electrodes through an external electrical circuit.
Figure 5.2.2: Some electrochemical
cells. Different reactions occur in each
half cell and the reactions can be
combined to write an equation for the
overall process occurring in the cell.
(a)
A simple example (including the half-equations occurring) is shown in
Figure 5.2.2.
(b)
V
Cu electrode
Salt bridge
Cu2+
Cu2+ + 2e– ➝ Cu
Zn electrode
V
Platinum electrode
Zn2+
Zn ➝ Zn2+ + 2e–
Salt bridge
Solution containing
Fe2+ and Fe3+ ions
Fe3+ + e– ➝ Fe2+
Platinum electrode
Solution containing
I2 and I– ions
2I– ➝ I2 + 2e–
Reduction potentials
By setting up electrochemical cells, chemists have been able to measure the
standard reduction potential, EƟ (also known as the standard electrode potential),
for a wide range of half cells.
Take it further
Standard reduction potentials are measured under specified conditions, including the use
of 1 mol dm–3 solutions, 1 bar pressure and 298 K. For more information about how standard
reduction potentials are measured see websites such as
http://www.chemguide.co.uk/physical/redoxeqia/introduction.html.
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Unit 5: Chemistry for Applied Biologists
The sign and magnitude of the EƟ provides a measure of the reducing power of
the reducing agent present in each half cell – the more negative the EƟ value, the
more powerful the reducing agent.
Notice that because each half cell process also contains an oxidising agent (on the
opposite side of the equation to the reducing agent), EƟ also provides a measure
of its oxidising power – the more positive the EƟ value, the more powerful the
oxidising agent.
Take it further
Tables of standard reduction potentials for standard chemical processes can be found online at sites
such as http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html. For information
on biochemical redox reactions it may be necessary to search using the relevant names of the
biological molecules involved.
Biochemical reduction potentials
Table 5.2.1 shows some reduction potentials for biochemically important halfreactions.
Table 5.2.1: The reduction potentials of
some half cells that occur in biological
systems. (Source: Biochemistry (Berg,
Tymoczko + Stryer, 2002), p495.)
Half-reaction
Standard reduction potential / V
NAD+ + H+ + 2e− ➝ NADH
−0.32
NADP+ + H+ + 2e− ➝ NADPH
−0.32
FAD + 2H+ + 2e− ➝ FADH2
−0.22
fumarate + 2H+ + 2e− ➝ succinate
+0.03
½O2 + 2H+ + 2e− ➝ H2O
+0.82
Notice that, although these processes are shown with one-way arrows, they are
all reversible processes and the reduction potential is a function of the process,
regardless of the direction of reaction.
Using reduction potentials
Link
You can learn more about the link
between EƟcell and ΔGƟ in Unit 6:
Physical Chemistry of Spectroscopy,
Surfaces and Chemical and Phase
Equilibria.
Reduction potentials for half cells can be used to predict the feasibility of
reactions. As in the previous sections, these predictions only apply to standard
conditions.
Calculating EƟcell
The half cells shown in Table 5.2.1 can be combined to make an electrochemical
cell. The maximum potential difference between the two electrodes (under
standard conditions) is known as the standard cell emf (EƟcell).
The significance of the EƟcell value for a particular cell is that it relates to the
reaction that will occur if the half cells are connected by a conductor. Reduction
occurs in one of the half cells and oxidation in the other.
EƟcell = reduction potential of − reduction potential of
reduction half cell oxidation half cell
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Unit 5: Chemistry for Applied Biologists
Relating EƟcell values to biochemical reactions
The following worked example will show how a given biochemical reaction can be
understood in terms of reduction potentials.
NADH is used to reduce O2 to water at the end of the electron transport chain:
½O2 + NADH + H+ ➝ H2O + NAD+
This equation can be broken down into two half-equations:
Reduction: ½O2 + 2H+ + 2e− ➝ H2O Reduction potential = +0.82 V
Oxidation: NADH ➝ NAD+ + H+ + 2e−
Reduction potential = −0.32 V
The EƟcell value for a cell in which this overall reaction could occur is therefore
0.82 − (−0.32) = + 1.14 V.
Using EƟcell values
The sign and magnitude of EƟcell can be used to give valuable information about
reactions:
•• a reaction will be feasible if EƟcell is positive
•• the more positive an EƟcell value is, the more favourable it will be
•• if EƟcell is greater than about +0.4 V, then the reaction is likely to be feasible
under all conditions, not just under standard conditions.
Take it further
As EƟcell and ΔGƟ are both indicators of the feasibility of a reaction, it will be no surprise to learn that
they are related. You can read more about the relationship at websites such as
http://chemistry.about.com/od/workedchemistryproblems/a/Cell-Potential-And-Free−
Energy-Example−Problem.htm.
Activity
During the process of aerobic respiration, succinate ions are oxidised to fumarate ions by the
action of the oxidising agent FAD. The reaction can be represented by the following equation:
succinate + FAD ➝ fumarate + FADH2
The half-equations for this process are:
succinate ➝ fumarate + 2H+ + 2e−
FAD + 2H+ + 2e− ➝ FADH2
•• Classify each of these half-equations as reduction or oxidation.
•• Use Table 5.2.1 to find the standard reduction potentials for each of the half cells represented
by these half-equations.
•• Calculate the EƟcell corresponding to a cell in which this reaction could occur.
•• Comment on the sign and magnitude of this EƟcell value.
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Unit 5: Chemistry for Applied Biologists
Portfolio activity (2.4)
Find an equation for a biological redox reaction, similar to those that have been discussed in this
section.
A suitable example could be the oxidation of malate to oxaloacetate by NAD+:
malate + NAD+ ➝ oxaloacetate + NADH+ + H+
Use ideas about reduction potentials to comment on the feasibility of this process. In your answer
you should:
•• write down the two half-equations that occur during this process
•• find reduction potentials for half cells in which these two half-equations can occur
•• use the reduction potential data to calculate the EƟcell value corresponding to a cell in which
this reaction could occur
•• comment on the feasibility of the reaction.
Checklist
At the end of this section you should be familiar with the following ideas:
 the feasibility of a chemical reaction can be predicted from a range of thermochemical data
ΔStotal , which includes contributions from ΔSsystem and the enthalpy change of the reaction,
must be positive for a reaction to be feasible
 ΔG is related to the amount of useful work which can be extracted from a reaction and must
be negative for a reaction to be feasible
 many biochemical reactions involve reduction and oxidation
 reduction and oxidation can be understood in terms of transfer of electrons or change in
oxidation numbers
 standard reduction potentials, measured in electrochemical cells, can be used to calculate
EƟcell
EƟcell must be positive if a reaction is to be feasible.
Further reading
Activities and assignments in this topic guide will require access to a database containing values
of ΔHƟ, ΔGƟ and SƟ, as well as reduction potentials (often called electrode potentials). As noted in
the Topic 5.1 Further Reading guide, the NIST Chemistry WebBook is very detailed and wide-ranging
(http://webbook.nist.gov/chemistry/). Data on reduction potentials can be found at
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html.
Coverage of entropy, Gibbs energy, redox reactions and redox equilibria will be found in many
general chemistry texts such as Advanced Chemistry (Clugston & Flemming, 2000). Chapters 13 and
14 cover this material.
Chemguide (http://www.chemguide.co.uk) covers much of the material from the section
on oxidation and reduction in the Inorganic Chemistry section and the material on reduction
potential in the Physical Chemistry section.
5.2: Studying the feasibility of reactions
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Acknowledgements
The publisher would like to thank the following for their kind permission to reproduce their
photographs:
Shutterstock.com: Anton Prado Photo.
All other images © Pearson Education
In some instances we have been unable to trace the owners of copyright material, and we would
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