Biochemistry: The Chemical Reactions of Living Cells, Volume 1 - D. Metzler 1980

Energetics of Biochemical Reactions
Thermodynamics
The First Law of Thermodynamics

The first law of Thermodynamics is the law of conservation of energy and the equivalence of work and heat. Work and heat represent different forms of energy and are interconvertible. A system can absorb heat from its external environment or release it. During The process of interaction with its surroundings, a system can perform work. The first law postulates that there exists a function E (sometimes denoted as U), called internal energy, which is determined solely by the Current state of the system and is independent of its past history. According to the first law, E can change only through The transfer of energy in the form of heat or the performance of work. In other words, this law states that energy can neither be created nor destroyed.

Class="center">Table 3-1 Units of Energy and Work and Values of Some Physical Constants

Joule, SI unit of energy

1 J = 1 kg∙m2∙s-1 =

= 1 N∙m (newton-meter) =

= 1 W∙s (watt-second) =

= 1 C∙V (coulomb-volt)

Thermochemical calorie

1 cal = 4.184 J

Large calorie

1 Cal = 1 kcal = 4.184 kJ

Work required to lift a weight of 1 kg to a height of 1 m (above sea level) = 9.807 J

Free energy of Hydrolysis of 1 mole of ATP at pH 7 and millimolar concentrations = —12.48 kcal = —52.2 kJ

Work required to increase the concentration of a substance 1000-fold (e.g., from 10-6 to 10-3 M) = 4.09 kcal = 17.1 kJ

Avogadro's number — number of particles in one mole of a substance N = 6.0220∙1023

Faraday constant 1F = 96 485 C∙mol-1

Coulomb 1 C = 1 A∙s (ampere-second)

= 6.241 ∙ 1018 (elementary charges)

Boltzmann constant

k = 1.38 07∙10-23 J∙deg-1

Gas constant R = N∙k

R = 8.3144 J∙deg-1∙mol-1 =

= 1.9872 cal∙deg-1∙mol-1 =

= 0.08206 L∙atm∙deg-1∙mol-1;

at 25° RT = 2.479 kJ∙mol-1

Unit of Temperature measurement, Kelvin degree, K; 0°C = 273.16 K lg x = 2.3026 ln x

Mathematically, the first law is expressed as:

∆E = E (products) — E (reactants) = Q—W,       (3-1)

where Q is the heat absorbed by the system from the external environment, and W is the work done by the system on its surroundings. Energy, heat, and work are measured in the same units. Chemists are still more accustomed to using calories (cal) or kilocalories (kcal); in the SI system, the unit of energy is the joule (Table 3-1). The work performed by a system can be mechanical (for example, work associated with changing external volume), electrical (charging a battery), or chemical (synthesis of a polypeptide from Amino Acids).



Last update: 06/08/2026

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