Biochem 4712

Keq can be determined from the change in standard free energy using the equation

Keq = e−∆G°/RT

A buffer contains 0.010 mol of lactic acid (pKa = 3.86) and 0.050 mol sodium lactate per liter of aqueous solution. A. Calculate the pH of this buffer. B. Calculate the pH after 5.0 mL of 0.50 M HCl is added to 1 liter of the buffer (assume the total volume will be 1005 mL).

4.56, 4.44

To make an acetate buffer at pH 4.76 starting with 500 mL of 0.1 M sodium acetate (pK acetic acid = 4.76), you could add

0.025 mol of HCl.

Consider the reaction A + B ⇄ C + D. After reaching equilibrium at 25°C, the following concentrations of reactants and products were measured: [A] = 10 μM, [B] = 15 μM, [C] = 10 μM, [D] = 10 μM. Calculate ∆G°' for this reaction.

1000 J/mol

What is the concentration of hydroxide ions at pH 10?

10^-4 M

Calculate the ∆G for a reaction with ∆H = 20. kJ/mol and ∆S =20. J/K·mol, that is carried out at 27°C.

14,000 J/mol

You prepare a solution by mixing 50 mL 0.10 M sodium acetate and 150 mL 1.0 M acetic acid (pKa = 4.76). Calculate the pH of this solution

3.28

The equilibrium constant of a reaction varies with pH but not temperature.

False

Which statement about Gibbs free energy is true?

Endergonic reactions have ∆G > 0

The term used to indicate the degree of randomness within a system is ______.

Entropy

A system is at thermodynamic equilibrium when its entropy has decreased to a minimum.

False

ΔG and ΔG ' mean the same thing.

False

A graduate student at SDSU wants to measure the activity of a particular enzyme at pH 4.0. To buffer her reaction, she will use a buffer system based on one of the acids listed below, which acid is most appropriate for the experiment?

Formic acid (Ka 1.78 × 10-4)

Gibbs free energy is defined as G = ______.

H - TS

A phosphate buffer solution at pH = pK1 = 2.15 would have equal amounts of phosphate in the _______ form and the H2PO4- form.

H3PO4

Phosphoric acid is a polyprotic acid, with pK values of 2.14, 6.86, and 12.38. Which ionic form predominates at pH 9.3?

HPO42-

Which aspect of the biochemical standard state is not different in physical chemistry?

Standard state temperature and pressure.

- +

The RXN is enthalpically opposed (endothermic) but entropically favored. It is spontaneous only at temps above T=delta H/ delta S

- -

The rxn is enthalpically favored but entropically opposed. It is spontaneous only at temps below T= deltaH/deltaS

A ΔG value of zero indicates that the reactions or processes are at equilibrium.

True

The value of ΔG°' for a given reaction is unaffected by other reactions in situ, even if these other reactions generate reactants or products of the given reaction.

True

After the reaction pyruvate + ATP PEP + ADP has reached equilibrium at 25°C [ATP] = 5 mM, [ADP] = 0.5 mM, [pyruvate] = 0.2 mM. Calculate the concentration PEP. Keq = 3.1 × 10−6. [PEP]eq

[PEP]eq = Enter your answer 6.2 · 10 Enter your answer -9 M

What is the name of the N-terminal amino acid in this peptide?

alanine

Variation of RXN spontaneity with signs of delta H and delta S

delta G= delta H-TdeltaS

Octane molecules dispersed in water tend to aggregate because that allows water molecules to be more

disordered

If gas molecules in an enclosed chamber are allowed to enter a second chamber, the resulting redistribution of gas molecules represents an increase in

entropy

Which function does NOT have units of energy?

entropy

What is the name of the proceeding functional group or linkage: >C=NH-?

imino

he strongest noncovalent interactions are

ionic interactions.

The insolubility of nonpolar molecules in water is due to the large ? which is the result of water molecules forming an ordered network surrounding nonpolar molecules.

negative entropy

A spontaneous process

occurs without the addition of free energy. B Option B: has a ∆G<0. C Option C: is exergonic. D Option D: is all of the above E Option E: is none of the above

Living organisms are classified thermodynamically as:

open systems

At a pH below its pKa, the ℰ-amino group of lysine is Select your answer

protonated

An increase in disorder in the system

results in the factor T∆S being positive.

Change in enthalpy (∆H) is best defined as

the heat transferred at constant pressure.

The hydrophobic effect is due largely to entropy changes in the solvent water.

true

Which statement about enthalpy is true?

∆H is approximately equal to ∆U, in most biochemical reactions.