6: Thermodynamics

Students calculate delta G and Keq, determine whether reactions are spontaneous, and interpret free energy diagrams for enzyme-catalyzed reactions.

LibreTexts reference: Unit 2, Chapter 1: Enzyme Thermodynamics

Matching Energy Terms to Requirement Categories

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Match each energy requirement category with its corresponding energy term.

Note: Each choice will be used exactly once.

	Your Choice	Prompt
	Drop Your Choice Here	1. releases energy
	Drop Your Choice Here	2. requires energy input

Drag one of the choices below:

• A. catabolic
• B. formation of polymers

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Matching Enzyme Catalysis Terms to Definitions

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Match each of the following terms related to enzyme catalysis with their corresponding definitions.
Note: Each choice will be used exactly once.

	Your Choice	Prompt
	Drop Your Choice Here	1. Cofactor
	Drop Your Choice Here	2. Ligand
	Drop Your Choice Here	3. Product
	Drop Your Choice Here	4. Transition state

Drag one of the choices below:

• A. any substance that forms a complex with a biomolecule to serve a biological purpose
• B. any substance that is produced as a result of a chemical reaction
• C. intermediate, short-lived, high energy state of the substrate before forming the product
• D. either metallic ions or small organic molecules required for enzyme activity

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True/False Statements About Chemical Reactions

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Which one of the following statements is TRUE regarding chemical reactions?

• A. For chemical reactions to happen, the chemical identity of both reactants and products remains the same.
• B. Chemical reactions are always exothermic.
• C. Chemical reactions only occur in the presence of light.
• D. Chemical reactions are involved in many important processes in biology.
• E. Chemical reactions only occur when energy is released.

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True/False Statements About Enzyme Cofactors

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Which one of the following molecular entities CANNOT be classified as an enzymatic cofactor?

• A. pyridoxal phosphate (PLP), a derivative of Vitamin B₆
• B. adenosine diphosphate (ADP)
• C. quinone, an organic compound involved in electron transport
• D. the structural protein, keratin
• E. aldosterone, a steroid hormone that acts on the kidney

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True/False Statements About Enzyme Equilibrium and Kinetics

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Which one of the following statements is TRUE concerning enzyme kinetics?

• A. enzymes stabilize the transition state in a chemical reaction
• B. enzymes alter the standard free energy (ΔG°′) of a chemical reaction
• C. enzymes force chemical reactions to go forward
• D. enzymes alter the equilibrium of the chemical reaction
• E. enzymes reduce the rate of a chemical reaction

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True/False Statements About Gibbs Free Energy (Delta G = Delta H - T Delta S)

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Which one of the following statements is TRUE regarding the Gibbs free energy, ΔG = ΔH – TΔS?

• A. Tis the temperature in degrees Kelvin
• B. When ΔS > 0 the reaction is called non-spontaneous
• C. enthalpy is associated with a state of disorder, randomness, or uncertainty
• D. When ΔS = 0 the reaction has reached equilibrium
• E. Negative entropy makes a reaction more favorable

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True/False Statements About Potential and Kinetic Energy

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Which one of the following is an example of kinetic energy rather than potential energy?

• A. an archery bow with the string pulled back
• B. a river flowing under a bridge
• C. a marathon runner at the start line
• D. a book hanging off the edge of a table
• E. a baseball in the hand of a pitcher

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True/False Statements About Thermodynamics and Kinetics

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Which one of the following statements is FALSE concerning thermodynamics and kinetics?

• A. In general, more order means more entropy.
• B. The equilibrium constant (K′_eq) is related to the standard change in free energy (ΔG°′) of a reaction.
• C. Enzymes alter the reaction kinetics by lowering the activation energy.
• D. A reaction is spontaneous if the standard change in free energy (ΔG°′) is negative.
• E. The change in Gibbs free energy (ΔG) of a reaction is related to the enthalpy and entropy changes of the reaction.

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True/False Statements About Enzyme Naming Patterns

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Enzymes are biological catalysts that speed up chemical reactions in living organisms.
Which one of the following choices is most likely an enzyme?
Hint: enzymes often have a distinct naming pattern that can help identify them.

• A. GMP
• B. albumin
• C. maltase
• D. estrogen
• E. triacylglycerol

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Energy Requirement Categories from Energy Terms

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Which one of the following energy requirement categories correspond to the energy term 'non-spontaneous'.

• A. releases energy
• B. requires energy input

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Enzyme Catalysis Terms from Definitions

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Which one of the following terms related to enzyme catalysis correspond to the definition 'a molecule (reactant) that is acted upon by an enzyme'.

• A. Active site
• B. Product
• C. Reactant
• D. Substrate

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Biochemical vs Chemical Standard Free Energy States

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The biochemical standard free energy change (delta G naught-prime, ΔG°′) differs from the chemical standard free energy change (delta G naught, ΔG°). Which factor is treated differently?

• A. all reactant concentrations are at 1 M
• B. pressure is different from 1 atm
• C. a buffer is required in the reaction mixture
• D. pH is fixed at 7 ([H⁺] = 1 × 10⁻⁷ M instead of 1 M)
• E. temperature is different from 298 K (25 °C)

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Exergonic and Endergonic Reaction Classification

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A reaction has a negative ΔG (ΔG < 0). This reaction is classified as:

• A. at equilibrium
• B. endergonic (energy-absorbing)
• C. activation-energy independent
• D. exergonic (energy-releasing)

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Gibbs Free Energy Change and Equilibrium Constant Relationships

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If the equilibrium constant (K′_eq) is less than 1, what is the sign of the standard transformed Gibbs free energy change (ΔG°′)?

• A. negative
• B. zero
• C. positive

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Gibbs Free Energy Equation Symbols and Meanings

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In the equation ΔG = ΔH − TΔS, match each symbol to the quantity it represents.

	Your Choice	Prompt
	Drop Your Choice Here	1. ΔH
	Drop Your Choice Here	2. ΔS
	Drop Your Choice Here	3. T

Drag one of the choices below:

• A. absolute temperature (Kelvin)
• B. change in entropy
• C. change in enthalpy

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Thermodynamics Law Statements

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The Second Law of Thermodynamics states:

• A. the total entropy of a system and its surroundings increases for a spontaneous process
• B. entropy of the universe is constant
• C. the total energy of a system and its surroundings is constant
• D. temperatures will always decrease in a spontaneous process

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First and Second Laws of Thermodynamics for Different Systems

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According to the second law of thermodynamics, the total entropy of a closed system is:

• A. always zero
• B. always increasing
• C. always decreasing
• D. always constant (conserved)
• E. cannot be determined without more information

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