Target: 10 Questions in 10 minutes

An IB Chemistry data booklet is helpful
1. Which of the following reactions or processes involve a decrease in entropy?
  • A.   I2(g)  → I2(s)
  • B.   Sublimation of dry ice
  • C.   KBr (s)  → K+(aq) + Br-(aq)
  • D.   Evaporation of water
2. Which of the following reactions will result in the largest increase in entropy at standard conditions?
  • A. C(s) + O2(g)  → CO2(g)
  • B. Fe2O3 (s) + 3CO(g) → 2Fe(s) + 3CO2(g)
  • C. 2NaOH(aq) + H2SO4(aq)  → Na2SO4(aq) + 2H2O(l)
  • D. CH4(g) + H2O(g) → CO(g) + 3H2(g)

3. Calculate the standard entropy change ΔSo,  in JK-1mo1-1, when 1 mol of ethanol combusts completely in oxygen at 298K, given the following data:

Substance ΔSo/JK-1mo1-1
CH3CH2OH(g) 161
O2(g) 205
H2O(l) 70
CO2(g) 214
 
  • A. -138
  • B.  -82
  • C. +82
  • D. +138
4. The spontaneous dissolving of sodium chloride in water is an endothermic process. What of the following statements is correct?
  • A.   The driving force of the process is the entropy change.
  • B.   The driving force of the process is the enthalpy change.
  • C.   The temperature of the water increases during the dissolving process.
  • D.   The dissolving process becomes less spontaneous at higher temperatures.
5. What is the standard Gibbs free energy change, ΔrGo, of the addition of 1mol of HBr to 1mol of ethene to make bromoethane? Using the data from table 13 in your IB data booklet.
  • A.  -147kJ
  • B.   -68kJ
  • C.   -41kJ
  • D.   +95kJ
6. Which of the following combinations of ΔH and ΔS will give a reaction that is only spontaneous at low temperatures?
  • A. ΔH positive and ΔS positive
  • B. ΔH negative and ΔS positive
  • C. ΔH positive and ΔS negative
  • D. ΔH negative and ΔS negative

7. An important reaction in the commercial production of nitric acid is:

2NH3(g) + 2½O2(g) ⇌  2NO(g) +3H2O(l)

For this reaction ΔrHo= - 586kJ and ΔrGo= - 506kJ.
What is the entropy change of this reaction at 25 °C in JK-1mo1-1?

  • A. -268
  • B. -0.268
  • C. +3.66
  • D. +3660
8. For a reaction A  → B+C, ΔHo = +150 kJ mo1-1 and ΔSo= +150 JK-1mo1-1. Which of the following statements is correct?
  • A.   The reaction is always spontaneous when T < 1K
  • B.   The reaction is always spontaneous when T < 1000K
  • C.   The reaction is always spontaneous when T > -272 °C
  • D.   The reaction is always spontaneous when T > +727 °C

9. An equilibrium mixture of a reaction consists mainly of products. Which of the following descriptions is always true? 

I. The equilibrium constant of the reaction is greater than 1
II. The ΔrGo is negative for this reaction
III. The reaction is fast in the forward direction
 
  • A.   I only
  • B.   II only
  • C.   I and II only
  • D.   I, II and III
10. A reversible reaction has a standard Gibbs energy change of 12.0 kJ at 500 °C. What is the value of the equilibrium constant of this reaction at this temperature?
  • A.   0.0557
  • B.   0.154
  • C.   0.997
  • D.   6.47