R1.2 Energy cycles in reactions Quiz
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5 questions, one answer each
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1. Using H–H 436, Cl–Cl 242 and H–Cl 431 kJ mol⁻¹, what is ΔH for H₂ + Cl₂ → 2HCl?
- A. +184 kJ
- B. −184 kJ
- C. −247 kJ
- D. +247 kJ
2. A reaction is exothermic when…
- A. more energy is absorbed breaking bonds than is released forming bonds
- B. more energy is released forming bonds than is absorbed breaking bonds
- C. no bonds are broken
- D. the products have more energy than the reactants
3. Which bond enthalpy is an exact value for its molecule rather than an average?
- A. C–H
- B. O–H
- C. H–Cl
- D. C–C
4. A → B has ΔH = +50 kJ and B → C has ΔH = −80 kJ. What is ΔH for C → A?
- A. +30 kJ
- B. −30 kJ
- C. +130 kJ
- D. −130 kJ
5. Why must all species be gases in a bond-enthalpy calculation?
- A. Bond enthalpies are defined for gaseous molecules, so changes of state are not included
- B. Liquids have no covalent bonds
- C. Gases react faster
- D. Solids cannot take part in reactions