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Chemistry Chapter 8 : Topic 7
Bond Breaking and Formation
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In a chemical reaction, energy is required to separate atoms that are already bonded together. This energy is supplied from the surroundings and increases the potential energy of the system. Which statement correctly describes this process?
Reasoning: Breaking chemical bonds requires energy input to overcome attractive forces between atoms; therefore, it is an endothermic process.
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During the formation of hydrogen molecules from hydrogen atoms, energy is observed to be released into the surroundings, making the surroundings warmer. This indicates that bond formation is:
Reasoning: When bonds form, energy is released because the system moves to a more stable, lower-energy state.
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Consider the reaction:H-H + Cl-Cl → 2H-ClIn this reaction, some bonds are broken and some are formed. Which statement is correct?
Reasoning: Breaking bonds is endothermic (energy absorbed), while forming bonds is exothermic (energy released).
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A student claims that all chemical reactions release energy because new substances are formed. Which correction is most appropriate?
Reasoning: Every reaction involves both processes; energy change depends on the balance between them.
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In an energy profile diagram, the energy level of reactants is higher than products. This indicates that:
Reasoning: When products have lower energy than reactants, excess energy is released, making it exothermic.
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Which statement best explains why energy must be supplied to break a covalent bond?
Reasoning: Bonds exist due to attractive forces; energy is needed to overcome them.
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During combustion of methane, more energy is released than is required to break the bonds in methane and oxygen. This means:
Reasoning: Exothermic reactions occur when energy released in bond formation exceeds energy required for breaking bonds.
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Which of the following correctly compares bond breaking and bond formation?
Reasoning: Energy is absorbed to break bonds and released when bonds form.
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A reaction absorbs 200 kJ to break bonds and releases 350 kJ when new bonds form. The overall reaction is:
Reasoning: Net energy =350-200=150 kJ released ⟹ exothermic
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Which statement best explains why bond formation leads to stability?
Reasoning: Formation of bonds lowers potential energy, making the system more stable.
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In an endothermic reaction overall, what can be said about bond energies?
Reasoning: Endothermic reactions occur when more energy is absorbed in breaking bonds than released.
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Why do all chemical reactions involve both endothermic and exothermic steps?
Reasoning: Every reaction involves breaking old bonds and forming new ones.
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Which energy change occurs when two hydrogen atoms form a hydrogen molecule?
Reasoning: Bond formation releases energy as the system becomes more stable.
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A reaction is carried out in a closed container, and the temperature increases without external heating. This suggests:
Reasoning: Temperature rise indicates exothermic process due to energy release from bond formation.
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Which of the following best describes activation energy in relation to bond breaking?
Reasoning: Activation energy is the minimum energy needed to initiate bond breaking in reactants.
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Why do exothermic reactions feel hot to the touch?
Reasoning: Energy released during bond formation increases surrounding temperature.
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Which situation best represents an endothermic process at the bond level?
Reasoning: Breaking O-O bond requires energy input, making it endothermic.
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