Energy in Bonding Mastery Test

Select the correct answer. How does a catalyst speed up a chemical reaction?

• by lowering the activation energy

• by lowering the ΔH of the reaction

• by raising the energy of the products

• by raising the energy of the reactants

Answer explanation

A catalyst speeds up a chemical reaction by lowering the activation energy, which is the energy barrier that must be overcome for the reaction to proceed. This allows more reactant molecules to participate in the reaction more quickly.

Select the correct answer. A chemist sets up a chemical reaction but finds that none of the reactant molecules have the required activation energy. What is the result?

• Products will form with less energy input.

• No products will be formed.

• The products will form too quickly.

• Products will convert to reactants.

Answer explanation

Since none of the reactant molecules have the required activation energy, the reaction cannot proceed. Therefore, no products will be formed.

Select the correct answer. How does activation energy affect a chemical reaction?

• It increases the energy of the reactants.

• It determines how difficult it is to start the reaction.

• It determines how much product can form.

• It decreases the energy of the products.

Answer explanation

Activation energy is the minimum energy required to start a reaction. Therefore, it determines how difficult it is to initiate the reaction, making the correct choice "It determines how difficult it is to start the reaction."

Select the correct answer from each drop-down menu. A carbon-carbon double bond has a greater bond energy than a carbon-carbon single bond. Because of the greater bond energy, a carbon-carbon double bond is _______ than a carbon-carbon single bond; and _______ than a carbon-carbon single bond.

• stronger, weaker

• longer, shorter

• weaker, stronger

• shorter, longer

Answer explanation

A carbon-carbon double bond has greater bond energy, making it stronger than a single bond. Consequently, it is also shorter due to the increased overlap of orbitals, while a single bond is weaker.

Select the correct location on the diagram. Which location represents the enthalpy of reaction?

What is the term for a reaction that absorbs heat?

• Endothermic

• Exothermic

Answer explanation

A reaction that absorbs heat is called an endothermic reaction. In contrast, an exothermic reaction releases heat. Therefore, the correct term for a heat-absorbing reaction is endothermic.

In an ENDOthermic reaction, ΔH is ​ (a)   and goes on the ​ (b)   side of a chemical equation because energy is ​ (c)  

• positive
• reactants
• absorbed
• released
• negative
• zero
• conserved
• products

The diagram shows that the reaction is ___________ and the enthalpy change is __________.

• endothermic, negative

• exothermic, negative

• endothermic, positive

• exothermic, positive