Chem 102 Final

Which of the following statements is correct? 1. Spontaneous changes only occur in the direction that leads to equilibrium 2. Exothermic reactions are always spontaneous 3. In any chemical reaction, energy must be conserved

1 and 3

The highest pH for an effective buffer occurs when the base is how many times as concentrated as the acid?

10

Which one of the following processes involves an increase in the entropy of the system?

2 Ag2O (s) -----> 4 Ag (s) + O2 (g)

An acid-base equilibrium system is created by dissolving 0.50 mol CH3CO2H in water to a volume of 1.0 L. What effect of adding 0.50 mol CH3CO2 to this solution? 1. The pH of the solution will equal 7.00 because the equal concentrations of a weak acid and its conjugate base are present. 2. Some CH3CO2H will ionize, increasing the concentration of CH3CO2 and increasing the pH 3. Some CH3CO2 will react with H3O+, increasing the concentration of CH3CO2H and reestablishing the solution equilibrium.

3 only

Which of the following are true? a) An effective buffer has a [base]/[acid] ratio in the range of 10-100 b) A buffer is most resistant to pH change when [acid]=[conjugate base] c) An effective buffer has very small absolute concentrations of acid and conjugate bases d)A buffer can not be destroyed by adding too much strong base. It can only be destroyed by adding too much strong acid e) None of the above

B) A buffer is most resistant to pH change when [acid]=[conjugate base]

If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.74, which of the following is true? a) [HCHO2]>[NaCHO2] b) [HCHO2]=[NaCHO2] c) [HCHO2]<[NaCHO2] d) [HCHO2]<<[NaCHO2] e) it is not possible to make a buffer of this pH from HCHO2 and NaCHO2

B) [HCHO2] = [NaCHO2]

At 298.15 Kelvin, all of the following substances have standard free energy of formation of zero EXCEPT a) Br2 (g) b) I2 (s) c) S8 (s) d) Cl2 (g) e) Hg (l)

Br2 (g) because Br2 is a liquid at room temperature

Which one of the following statements is TRUE? a) A buffer is an aqueous solution composed of two weak acids b) A buffer can absorb an unlimited amount of acid or base c) A buffer resists pH change by neutralizing added acids and bases d) A buffer does not change pH when strong acid or base is added e) NONE of the above

C: A buffer resists pH change by neutralizing added acids and bases

Thermodynamics can be used to determine all of the following EXCEPT: a) the temperature at which a reaction is spontaneous b) the extent to which a reaction occurs c) the direction in which a reaction is spontaneous d) the rate of reaction e) the entropy change of a reaction

D: the rate of reactions because that is kinetics

When mixed in appropriate amounts, each of the following mixtures can produce an effective buffer solution EXCEPT: a) HCl and NaH2PO4 b) Na2HPO4 and Na3PO4 c)NaHCO3 and Na2CO3 d) NaH2Po4 and Na2HPO4 e) NaOH and NaF

E) NaOH and NaF because common ion is Na+ and that will not produce an acid/conjugate base pair

All of the following statements concerning acid-base buffers are true EXCEPT:

buffers are used as colored indicators in acid-base titrations

The second law of thermodynamics states that

in a spontaneous process, the entropy of the universe increases

What is the mathematical expression for Henderson-Hasselbalch equation?

pH= pKa + log ([conjugate base]/[acid])

If delta G(knot) > 0 for a reaction at all temperatures, then delta H(knot) is _________ and delta S(knot) is ________

positive; negative