Thermochemistry

Concept: Thermodynamics

7m

Concept: Kinetic and Potential Energy

12m

Concept: Gibbs Free Energy and Chemical Reactions

16m

Problem: Spontaneous reactions happen quickly.

1m

Problem: Exergonic reactions occur spontaneously, and do not require energy input to proceed.

1m

Problem: The energy required for a reaction to proceed is __________.

1m

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Thermochemistry Additional Practice Problems

The ΔGº values for the two reaction shows below are given:

Oxaloacetate + actyl CoA + H2O → citrate + CoASH (ΔGº=-32.2 kJ/mol; enzyme: citrate synthase)

Oxaloacetate + acetate → citrate (ΔGº = -1.9 kJ/mol; enzyme: citratesynthase)

Write the advanced hydrolysis reaction for acetyl CoA.

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A. What is the ΔGº' for the reaction below, given that the ΔGº' for ATP hydrolysis to ADP is -30.5 kJ/mol and the ΔGº' for the hydrolysis of 1,3-bisphosphoglycerate to 3-phosphoglycerate is -49.4 kJ/mol?

1,3-bisphosphoglycerate + ADP → 3-phosphoglycerate + ATP

B. What is the equilibrium constant for this reaction?

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The graph below shows energy changes in a specific chemical reaction. Which terms best describe the reaction?

A. Endergonic and nonspontaneous

B. Endergonic and spontaneous

C. Exergonic and spontaneous

D. Exergonic and nonspontaneous

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Study the figure shown below. What does letter A depict?

A. substrate concentration

B. energy of the products

C. energy of activation

D. energy of the reactant

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In the pathway below, B → C is coupled with ADP → ATP. Categorize the reactions as endergonic or exergonic.

A. B → C is endergonic and ADP → ATP is exergonic.

B. ADP → ATP is endergonic and B → C is exergonic.

C. Both B → C and ADP → ATP are endergonic.

D. Both B → C and ADP → ATP are exergonic.

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Match the following equations 1-4 with the energy diagram that best describes the free-energy transitions along the reaction pathway by filling in the equation number in the box under each respective curve. 

After you have identified a match for each equation, indicate the positions of A, B, and C (if applicable) on the free-energy curves.

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Exergonic reactions do not require activation energy to get started since they release energy. 

a. True

b. False

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The first and second laws of thermodynamics apply to nonliving systems like gasoline engines but do not apply to reactions in living cells. 

a. True

b. False

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Movement of molecules down a concentration gradient is an example of:

a. Potential energy

b. Oxidation

c. Reduction

d. Active transport

e. Kinetic energy

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Plants require light to perform photosynthesis in which glucose is formed from carbon dioxide and water. This is a _____ reaction. 

a. Exergonic

b. Kinetic energy

c. Endergonic

d. Potential energy

 

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The wood in a match is made up of cellulose, which is a polymer of glucose molecules. When you light the match, heat and light are given off, indicating that a ________ reaction is occurring. 

a. Endergonic

b. Kinetic energy

c. Exergonic

d. Potential energy

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An endergonic reaction is a reaction that: 

a. Requires an input of energy

b. That typically builds complex molecules from smaller molecules

c. Releases energy to its surroundings

d. Both releases energy to its surroundings and typically build complex molecules from smaller molecules are correct

e. Both requires an input of energy and typically builds complex molecules from smaller molecules are correct

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Entropy is: 

a. Order

b. Complexity

c. Disorder

d. Both order and disorder are correct

e. Both complexity and disorder are correct

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Which statement is not part of the first law of thermodynamics? 

a. The amount of energy in the universe is constant

b. Energy cannot be created or destroyed

c. Energy can be converted to other forms of energy

d. Any energy transformation loses some energy to its surroundings as heat

e. None of these are correct

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An example (examples) of potential energy is (are): 

a. Chemical bonds and concentration gradients

b. Light and chemical bonds

c. Concentration gradients

d. Chemical bonds

e. Light

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The reaction A+B→E requires +8.2 kcal of energy. Which of the following could be coupled to the above reaction:

a. D+C→F = -7.2 kcal

b. X+Y→Z = +10 kcal

c. M+N→O = -15 kcal

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A reaction with a negative ΔG is referred to as an:

a. endergonic reaction

b. entropy reaction

c. exergonic reaction

d. activation reaction

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As energy is being reconverted through the many forms, it is continuously lost as

a. electricity

b. light

c. sound

d. heat

e. chemical energy

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A chemical reaction in which the products contain less energy than the _______ will tend to proceed spontaneously.

a. reactants

b. enzymes

c. coenzymes

d. substrates

e. cofactors

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Reactions that occur spontaneously and release free energy are called

a. activation reactions

b. exergonic reactions

c. catabolistic reactions

d. thermodynamic reactions

e. end-product reactions

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The ΔG for a particular uncoupled reaction in a cell is -5.0 kcal/mol. Based on that information, which of the following is false

a. The reaction releases free energy.

b. An enzyme will likely be utilized to allow the reaction to proceed in a useful time frame.

c. The rate of this uncatalyzed reaction will be determined by the quantity of activation energy required to initiate it.

d. The products of the reaction have more free energy than the reactants.

e. The transition state (reactants pass through this state on their way to becoming products) possesses the most free energy.

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