Bioenergetics & Thermodynamics

A reaction that is exergonic will be spontaneous. True or False?

An endergonic reaction requires an input of energy to proceed. True or False?

By definition, a spontaneous reaction is one in which

• energy is released

• energy is absorbed

• the energy change is zero

• the reaction is fast

• the reaction is slow

• true

• false

• a positive or negative ΔG tells us which direction the reaction will proceed

• ΔG depends on the concentration of reactants and products

• ΔG is affected by temperature

• ΔG is affected by pressure and pH

• ΔG is negative for endergonic reactions

Which equation defines a system at equilibrium?

• ΔG > 0

• ΔG° = ΔG

• ΔG  = 0

• ΔG  = RT ln ([products]/[reactants])

Consider these reactions:

ATP → ADP + Pi ΔG°' = −31 kJ/mol

glucose-6-phosphate → glucose + Pi ΔG°' =  −13 kJ/mol

glucose + ATP → glucose-6-phosphate + ADP ΔG°' = ?

What is the ΔG°' of the last reaction?

• -44 kJ/mol

• -18 kJ/mol

• +18 kJ/mol

• +44 kJ/mol

Answer explanation

direction of second equation is in opposite direction to combined reaction, ∆G will have opposite energy in combined reaction.

 ∆G°' = -31 + 13 = -18  kJ/mol

If the  ∆G°' of the reaction A → B is -40 kJ/mol, under standard conditions the reaction ________

• is at equilibrium

• will never reach equilibrium

• will not occur spontaneously

• will proceed at a rapid rate

• will proceed spontaneously from left to right

The reaction A + B → C has a ΔG0' of –20 kJ/mol at 25 °C.  

Starting under standard conditions, one can predict that ________

• at equilibrium, the concentration of B will exceed the concentration of A

• at equilibrium, the concentration of C will be less than the concentration of A

• at equilibrium, the concentration of C will be much greater than the concentration of A or B

• C will rapidly break down to A + B

• when A and B are mixed, the reaction will proceed rapidly toward formation of C

A chemical reaction is faster when

• ∆G > 0

• ∆G < 0

• the activation energy is high

• the activation energy is low