16 topics with concise breakdowns: definitions, key facts, and class questions.
In this chapter, we analyze the fundamental laws governing chemical processes. You will learn why some reactions occur instantly and release heat, while others require enzymes and harsh conditions. This provides the essential foundation for understanding biochemical processes in the human body.
This section covers chemical thermodynamics (enthalpy and Hess's law) and kinetics (reaction rates, activation energy, law of mass action). A large separate block is devoted to solutions: the theory of electrolytic dissociation, hydrogen ion exponent ($pH$) calculation, and ionic equilibria, including the behavior of acids and bases as electrolytes.
During colloquia and exams, professors most frequently ask about $pH$ calculations, the application of Hess's law to assess energy balance, and the conditions for shifting chemical equilibrium. Pay special attention to catalysis mechanisms and writing ionic equations—without a firm grasp of these topics, passing biochemistry and pharmacology in the senior years is impossible.
Do spontaneous reactions always proceed with heat release?
No. Although heat release is a frequent condition, spontaneous endothermic processes do exist. For example, the dissolution of sodium thiosulfate pentahydrate in water proceeds spontaneously, but the solution cools down significantly.
Why is the heat of formation of simple substances equal to zero?
In thermochemistry, the stable state of simple substances under standard conditions is conventionally taken as the baseline, zero energy level. This is necessary to establish a reference point for calculations.
Why is it difficult to determine the time of complete completion of a chemical reaction?
As the reactants are consumed, their concentration drops, and the process naturally slows down. Because of this, the moment of absolute completion of the reaction becomes indefinite, making it more convenient in practice to use the half-life period.
What is the temperature coefficient of reaction rate?
This is a numerical value (usually between 2 and 4) that shows how many times the rate of a specific chemical reaction increases when the system's temperature is raised by exactly 10 °C.
Why is it impossible to derive the kinetic equation for a complex reaction directly from the chemical equation?
A complex reaction proceeds through a chain of hidden intermediate stages. Therefore, the exponents in the actual rate equation (reaction orders) do not match the final stoichiometric coefficients.
Can a catalyst be used to start an impossible reaction?
No. A catalyst accelerates exclusively those reactions that are thermodynamically possible and proceed spontaneously.
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