AP Chemistry Practice Quiz: Bond Enthalpies
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 9 questions to check your progress.
Question 1 of 9
All Questions (9)
A) Changes in the kinetic energy of the molecules.
B) The breaking and/or forming of chemical bonds.
C) The collision frequency between reactant particles.
D) The presence of a catalyst.
Correct Answer: B
The provided content explicitly states that 'During a chemical reaction, bonds are broken and/or formed, and these events change the potential energy of the system.' The other options describe factors that affect reaction rate or energy state but are not the direct cause of the potential energy change described by bond enthalpies.
A) releases energy.
B) requires energy.
C) is energetically neutral.
D) occurs only in exothermic reactions.
Correct Answer: B
The content specifies that 'The average energy required to break all reactant bonds can be estimated by summing their average bond energies.' The key word 'required' indicates that breaking bonds is an endothermic process that consumes energy from the surroundings.
A) Energy is absorbed from the surroundings.
B) Energy is released to the surroundings.
C) There is no change in the system's energy.
D) The potential energy of the system increases.
Correct Answer: B
The provided text states that bond energy values can be used to estimate the 'energy released when forming product bonds.' This release of energy is an exothermic process, lowering the potential energy of the system.
A) The energy required to break reactant bonds is greater than the energy released forming product bonds.
B) The energy released forming product bonds is greater than the energy required to break reactant bonds.
C) Only bond formation occurred; no bonds were broken.
D) The average bond energy of reactants and products is equal.
Correct Answer: B
The content directly states: 'If energy released is greater than energy required, the reaction is exothermic.' This means that more energy is given off by the formation of stable product bonds than was consumed to break the reactant bonds.
A) exothermic.
B) endothermic.
C) spontaneous.
D) energetically neutral.
Correct Answer: B
As stated in the provided text, if the energy required (to break bonds) is greater than the energy released (from forming bonds), the reaction is endothermic. The system must absorb a net amount of energy from the surroundings.
A) ΔH = Σ(bond energies of bonds formed) - Σ(bond energies of bonds broken)
B) ΔH = Σ(bond energies of bonds broken) - Σ(bond energies of bonds formed)
C) ΔH = Σ(bond energies of bonds broken) + Σ(bond energies of bonds formed)
D) ΔH = Σ(bond energies of products) / Σ(bond energies of reactants)
Correct Answer: B
The overall enthalpy change is the net result of the energy input to break bonds and the energy output from forming bonds. The calculation is based on the sum of energies for bonds broken (an energy cost, positive term) minus the sum of energies for bonds formed (an energy release, negative term).
A) The bonds in the reactants were, on average, stronger than the bonds in the products.
B) The bonds in the products were, on average, stronger than the bonds in the reactants.
C) The number of bonds broken was exactly equal to the number of bonds formed.
D) The reaction involved only the formation of bonds.
Correct Answer: B
Stronger bonds release more energy when they are formed. For a reaction to be exothermic, the energy released from forming the product bonds must exceed the energy required to break the reactant bonds. This implies that the product molecules contain stronger, more stable bonds.
A) The potential energy of the system decreased because weak bonds were formed.
B) The energy absorbed to break the reactant bonds was less than the energy released when forming the product bonds.
C) The bonds in the reactant molecules were, on average, stronger than the bonds formed in the product molecules.
D) The product bonds are more stable than the reactant bonds.
Correct Answer: C
An endothermic reaction requires a net input of energy. This occurs when more energy is needed to break the bonds of the reactants than is released by the formation of the product bonds. Stronger bonds require more energy to break, so the reactant bonds must be stronger on average than the product bonds.
A) [Energy to form one A-B bond] - [Energy to break one A-A bond]
B) [Energy to break one A-A bond] - [2 × Energy to form one A-B bond]
C) [Energy to break one A-A bond + Energy to break one B-B bond] - [2 × Energy to form one A-B bond]
D) [2 × Energy to form one A-B bond] - [Energy to break one A-A bond + Energy to break one B-B bond]
Correct Answer: C
The calculation for enthalpy change is Σ(bonds broken) - Σ(bonds formed). In this reaction, one A-A bond and one B-B bond are broken. Two A-B bonds are formed. Therefore, the correct setup is the sum of the energies for the A-A and B-B bonds minus two times the energy for the A-B bond.