Question: Which phrase describes the initial input of energy that is needed to break bonds in a chemical reaction?

Answer: activation energy

Question: The diagram represents the reaction of hydrogen gas and oxygen gas to produce water. Which statement best describes the reaction?

Answer: More energy is released in the formation of the products than is needed to break the bonds of the reactants, so the reaction is exothermic.

Question: Hydrogen gas (H2) and oxygen gas (O2) combine. Which change occurs that indicates a release of bond energy?

Answer: a loud popping noise

Question: Which statement explains why the electrolysis of hydrochloric acid (HCl) is an endothermic reaction?

Answer: It requires electricity to sustain the reaction.

Question: Use the chemical equation to answer the question.

2H2(g) + O2(g) → 2H2O(l)

Which statement describes the breaking and forming of bonds in the reaction?

Answer: The reaction requires breaking one O=O bond and two H-H bonds, and then forming four O-H bonds.