Target: 10 Questions in 10 minutes

An IB Chemistry data booklet is helpful

1. Using the information below, what is the enthalpy change of reaction (∆rH) for the oxidation of SO2 to SO3?

S(s) + O2(g)  → SO2(g) ∆rH = x
S(s) + 3/2O2(g)  → SO3(g)       ∆rH = y
 
  • A.   x+y
  • B.   x-y
  • C.   -x+y
  • D.  -x-y
2+3: The reduction of nitrogen monoxide by carbon monoxide is used industrially to remove both pollutants simultaneously in flue gas. The equation for this reaction is:

2NO(g) + 2CO(g)  → N2(g) + 2CO2(g)

2. What is the enthalpy change of this reaction, ∆rH, given the following data?

½N2(g)  + ½O2(g) → NO(g)        ∆rH = +90.3 kJ mol-1

C(s) + ½O2(g) → CO(g)        ∆rH = -110.5 kJ mol-1

C(s) + O2(g)  → CO2(g)        ∆rH = -393.5 kJ mol-1

  
  • A.   + (90.3) - (110.5) + (393.5)
  • B.   + 2(90.3) - 2(110.5) + 2(393.5)
  • C.   - (90.3) + (110.5) - (393.5)
  • D.   - 2(90.3) + 2(110.5) - 2(393.5)
3. The reaction above can be accelerated using a copper-based catalyst. How does the enthalpy change of this reaction, ∆rH, change in the presence of a catalyst?
  • A.   ∆rH becomes more endothermic.
  • B.   ∆rH does not change.
  • C.   ∆rH becomes more exothermic.
  • D.   Cannot determine, more information is needed.

4. To indirectly determine the enthalpy change of reaction for the thermal decomposition of potassium hydrogencarbonate to potassium carbonate, both compounds are reacted with excess dilute hydrochloric acid individually, and the enthalpy change of each reaction is measured:

KHCO3(s) + HCl(aq)  → KCl(aq)+H2O(l)+CO2(g)        ∆H1

K2CO3(s)+2HCl(aq)  → 2KCl(aq)+H2O(l)+CO2(g)       ∆H2

What is the enthalpy change for the following reaction, calculated using Hess’s Law?

2KHCO3(s)  → K2CO3(s)+ H2O(l)+CO2(g)

  
  • A.   2∆H1-∆H2
  • B.   ∆H1-∆H2
  • C.   -∆H1+∆H2
  • D.  -2∆H1+∆H2  
5. On the potential energy profile below, the following reaction is shown:

M + N + O  → Q + R

P is an intermediate in this reaction.

Energy changes in reaction - Hess's law

  
Which arrow A to D in the diagram above shows the ∆H of the reaction?

6. Using the following information, what is the value of ΔrH of the decomposition of CuSO4.5H2O(s) to CuSO4(s)?

CuSO4(s)  → CuSO4(aq)          ∆rH = - 66.1 kJ mol-1

CuSO4. 5H2O(s)  → CuSO4(aq)        ∆rH = +11.7 kJ mol-1
  • A.  +77.8 kJ mol-1
  • B.  +54.4 kJ mol-1
  • C.  –54.4 kJ mol-1
  • D.  -77.8 kJ mol-1

7. Cyclohexene undergoes addition reaction with bromine to form 1,2-dibromocyclohexane. The equation for this reaction is:

Cyclohexane reaction with bromine diagram

Bond enthalpies are:

  Average Bond Energy (kJ mol-1)
C-C 346
C=C 614
Br-Br 193
C-Br 285
 

What is the enthalpy change of this reaction, in kJ, calculated using the bond enthalpies given above?

  • A.   -109
  • B.   -31
  • C.   +109
  • D.  +176
8. Which of the following equations represent the bond enthalpy of H-Br?
  • A.   H+(g) + Br-(g)  → HBr(g)
  • B.   H(g) + Br(g)  → HBr(g)
  • C.   HBr(g)  → ½H2(g) + ½Br2(g)
  • D.   H2(g) + Br2(g)  → 2HBr(g)
9. The equation below shows the incomplete combustion of methanol:

CH3OH(l) + O2(g)  → CO(g) + 2H2O(l)

What is the enthalpy change calculated using the data given below?

  Approximate Average Bond Energy (kJ mol-1)
C-H 410
C-O 360
C=O 800
CO triple bond 1070
O=O 500
O-H 460

and:

CH3OH(l)  → CH3OH(g)    ∆H = 35 kJ mol-1
H2O(l)  → H2O(g)   ∆H = 44 kJ mol-1
 
  • A.   -413 kJ mol-1
  • B.   -369 kJ mol-1
  • C.   -360 kJ mol-1
  • D.   +351 kJ mol-1

10. For the reaction below, ∆Ho = -92 kJ mol-1.

N2(g) + 3H2(g)  → 2NH3(g)

Which of the following statements are true?

I. The energy required to break the bonds in the reactants is greater than the energy released when making the bonds in the products.
II. The reactants are less stable than the products.
III. The bonds in the reactants are weaker than the bonds in the products.
  • A. I and II only
  • B. I and III only
  • C. II and III only
  • D. I, II and III