6: Thermodynamics

Enzyme functions, substrate binding, and energy changes in reactions.

LibreTexts reference: Enzyme Thermodynamics

Energy Requirement Categories and Energy Terms

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

Drag one of the choices below:

• A. digestion
• B. dehydration reactions

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Energy Terms and Their Categories

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

• releases energy 
• requires energy input 

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True/False Statements About Chemical Reactions

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

• Chemical reactions are always either exothermic or endothermic. 
• Chemical reactions always result in a decrease in the number of atoms. 
• Chemical reactions always result in a decrease in the total energy of the system. 
• Chemical reactions only occur in the presence of light. 
• Reactions that occur in living organisms are NOT chemical reactions. 

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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 FALSE about the Gibbs free energy, ΔG = ΔH – TΔS?

• When ΔG > 0 the reaction is calledspontaneous 
• enthalpy is associated with the amount of heat exchanged with the environment 
• Tis the temperature in degrees Kelvin 
• ΔH is the change in enthalpy 
• When ΔG = 0 the reaction has reached equilibrium 

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True/False Statements About Thermodynamics and Kinetics

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Which one of the following statements is TRUE of thermodynamics and kinetics?

• Enzymes change the standard Gibbs free energy change (ΔG°′) of a reaction. 
• Enzymes change the rate of a reaction. 
• The third law of thermodynamics states that the entropy of a system is conserved. 
• Thermodynamics determines the rate of a reaction. 
• The rate of a reaction is independent of temperature. 

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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?

• colder temperature makes a reaction more favorable
• Tis the temperature in degrees Celcius
• When ΔG > 0 the reaction is called non-spontaneous
• ΔG is the change in entropy
• entropy is associated with the heat content of a system

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True/False Statements About Thermodynamics and Kinetics

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

• Enzymes do NOT change the equilibrium constant (K′_eq) of a reaction.
• Kinetics depends only on the ratio of product and substrates.
• The change in Gibbs free energy (ΔG) of a reaction is related to the enthalpy and entropy changes of the reaction.
• Equilibrium is reached when the rate of the forward and reverse reactions is equal.
• Enzymes lower the activation energy, which affects the reaction kinetics.

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Energy Requirement Categories for Energy Terms

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Which one of the following energy requirement categories correspond to the energy term 'formation of polymers'.

• releases energy
• requires energy input

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Biochemical vs Chemical Standard Free Energy States

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Which condition is specified differently in the biochemical standard state (delta G naught-prime, ΔG°′) compared to the chemical standard state (delta G naught, ΔG°)?

• pressure is different from 1 atm
• temperature is different from 298 K (25 °C)
• all reactant concentrations are at 1 M
• pH is fixed at 7 ([H⁺] = 1 × 10⁻⁷ M instead of 1 M)
• ionic strength is fixed at 0.1 M

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Exergonic and Endergonic Reaction Classification

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A reaction is classified as exergonic. Which statement about ΔG is true?

• ΔG < 0 (negative)
• ΔG = 0 (the reaction is at equilibrium)
• no activation energy is required for this reaction
• ΔG > 0 (positive)

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Free Energy and Equilibrium Constant Relationships

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

• negative
• zero
• positive

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Gibbs Free Energy Equation Symbols and Meanings

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Given the relationship ΔG = ΔH − TΔS, identify what each symbol stands for.

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

Drag one of the choices below:

• A. absolute temperature (Kelvin)
• B. change in entropy
• C. change in Gibbs free energy

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Thermodynamics Law Statements

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Which statement best describes the First Law of Thermodynamics?

• free energy of the universe always decreases
• entropy of the system always increases for a spontaneous process
• the total entropy of a system and its surroundings increases for a spontaneous process
• the total energy of a system and its surroundings is constant

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Energy and Entropy Conservation in Open, Closed, and Isolated Systems

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According to the first law of thermodynamics, the total energy of an isolated system is:

• always zero
• always increasing
• always decreasing
• always constant (conserved)
• cannot be determined without more information

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