iGCSE Chemistry 0620 Extended - 5.1 Exothermic and endothermic reactions- Exam Style Questions Paper 2- New Syllabus
▶️ Answer/Explanation
\(\Delta H = \sum(\text{Bond energies of bonds broken}) – \sum(\text{Bond energies of bonds formed})\)
Bonds broken: C=C (614) + H−H (436) = 1050 kJ
Bonds formed: C−C (350) + 2 × C−H (2 × 410 = 820) = 1170 kJ
\(\Delta H = +1050 – 1170 = -120\,\text{kJ/mol}\)
The negative value indicates an exothermic reaction.
✅ Answer: (B)
Bonds broken: C=C (614) + H−H (436) = 1050 kJ
Bonds formed: C−C (350) + 2 × C−H (2 × 410 = 820) = 1170 kJ
\(\Delta H = +1050 – 1170 = -120\,\text{kJ/mol}\)
The negative value indicates an exothermic reaction.
✅ Answer: (B)
▶️ Answer/Explanation
In an endothermic process, energy is absorbed from the surroundings. This causes the temperature of the surroundings (the mixture) to decrease.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
In an exothermic reaction, the energy released when new bonds are formed in the products is greater than the energy required to break bonds in the reactants. This results in a net release of energy to the surroundings.
(A) is false — vigorous reactions at room temperature have low activation energy.
(B) is false — bond making is always exothermic, regardless of \(\Delta H\) sign.
(D) is false — positive \(\Delta H\) means endothermic; energy is absorbed from the surroundings.
✅ Answer: (C)
(A) is false — vigorous reactions at room temperature have low activation energy.
(B) is false — bond making is always exothermic, regardless of \(\Delta H\) sign.
(D) is false — positive \(\Delta H\) means endothermic; energy is absorbed from the surroundings.
✅ Answer: (C)