Triple science: iGCSE Chemistry Only  

Q1-2:
The energy level diagram for a reaction with and without a catalyst is shown below:

chemical reaction energy diagram

  
1. Which letter represents the activation energy for the uncatalysed reaction?
2. Which letter represents the activation energy for the catalyzed reaction?

Q3-4:

An energy level diagram for a reaction is shown here:

chemical reaction energy level diagram 2

3. Which type of energy change does this diagram represent and what sign should ΔH be given?

 
  Type of change Sign of ΔH
A exothermic positive
B exothermic negative
C endothermic positive
D endothermic negative

4.For which reaction(s) would this be an appropriate diagram?

  I. CH4 + 2O2 → CO2 + 2H2O
II. C + O2 →  CO2
III. 2H2+ O2 → 2H2O
 
  • A.   all of them
  • B.   I and II only
  • C.  II and III only
  • D.   none of them

5. Which of the following statements about catalysts are true? A catalyst..

     I. provides an alternative pathway with lower activation energy
   II. provides an alternative pathway with a lower enthalpy change
 III. is chemically unchanged at the end of the reaction
 
  • A.   I and II
  • B.   I and III
  • C.   II and III
  • D.   all of them

6. Which of the following is correct about the energy changes involved during bond breaking and bond making?

  Bond breaking Bond making
A exothermic endothermic
B exothermic exothermic
C endothermic endothermic
D endothermic exothermic

7. For the reaction:

R2 + S2 → 2RS

Which combination of bond strengths would produce the most exothermic reaction?

  Bond strength in R2 and S2 Bond strength in RS
A weak weak
B weak strong
C strong weak
D strong strong

Q8-10:
The following equation represents the conversion of sulfur dioxide to sulfur trioxide:

supfur trioxide reaction

Average bond energies for the bonds involved are:
O=O bond          496 kJ/mol
S=O bond           523 kJ/mol
8. The energy required to break the bonds in the reactants is..
  • A.   1542 kJ/mol
  • B.   1569 kJ/mol
  • C.   2588 kJ/mol
  • D.   3138 kJ/mol
9. The energy given out when the bonds in the products form is..
  • A.   1542 kJ/mol
  • B.   1569 kJ/mol
  • C.   2588 kJ/mol
  • D.   3138 kJ/mol
10. The enthalpy change, ΔH, for this reaction is..
  • A.   +550 kJ/mol
  • B.   -550 kJ/mol
  • C.   +27 kJ/mol
  • D.  -27 kJ/mol