In chemistry, the standard state for as solution is 1 M (see Table17.2). This means that each solute concentration expressed in molarity is divided by 1 M. In biological systems, however, we define the standard state for the H+ ions to be 1×10−7 M because the physiological pH is about 7. Consequently, the change in the standard Gibbs free energy according to these two conventions will be different involving uptake or release of H+ ions, depending on which convention is used. We will therefore replaced ΔG° with ΔG°′, where the prime denotes that it is the standard Gibbs free-energy change for a biological process. (a) Consider the reaction
where x is a
(b) NAD+ and NADH are the oxidized and reduced forms of nicotinamide adenine dinucleotide, two key compounds in the
ΔG° is −21.8 kJ/mol at 298 K. Calculate ΔG°′. Also calculate ΔG using both the chemical and biological conventions when [NADH] = 1.5 × 10−2 M, [H+] = 3.0 × 10−5 M, [NAD] = 4.6 × 10−3 M, and
(a)
Interpretation:
The standard free energy
Concept Introduction:
Free energy
Free energy (Gibbs free energy) is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work. The free energy is represented by the letter
Explanation of Solution
The given reverse process reaction is,
Let us consider the following free energy equation,
Where
Here the chemical standard of (1M), we can write has,
For the biological standard state, so we can write as,
We set the two equations (1) and (2) equal to each other,
Given the reverse reaction
(b)
Interpretation:
The standard free energy value
Concept Introduction:
Thermodynamics is the branch of science that relates heat and energy in a system. The four laws of thermodynamics explain the fundamental quantities such as temperature, energy and randomness in a system. Entropy is the measure of randomness in a system. For a spontaneous process there is always a positive change in entropy. Free energy (Gibbs free energy) is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work. The free energy is represented by the letter G. All spontaneous process is associated with the decrease of free energy in the system. The equation given below helps us to calculate the change in free energy in a system.
Where,
Free energy (Gibbs free energy) is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work. The free energy is represented by the letter
Explanation of Solution
Next we calculate the standard free energy
We can now calculate
The chemical standard state is,
The biological standard state is,
The expected free energy
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Chapter 17 Solutions
CHEMISTRY 4
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- Explain why absolute entropies can be measured.arrow_forwardCalculate the standard Gibbs free-energy change when SO3 forms from SO2 and O2 at 298 K. Why is sulfur trioxide an important substance to study? (Hint: What happens when it combines with water?)arrow_forwardTable 16-1 shows the possible arrangements of four molecules in a two-bulbed flask. What are the possible arrangements if there is one molecule in this two-bulbed flask or two molecules or three molecules? For each, what arrangement is most likely?arrow_forward
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