Endothermic and Exothermic Reactions: Mastery Test

Select the correct answer. What kind of reaction occurs when a molecule of glucose reacts with oxygen to give carbon dioxide and water?

• an exothermic reaction

• an endothermic reaction

• a synthesis reaction

• an irreversible reaction

Answer explanation

The reaction of glucose with oxygen to produce carbon dioxide and water releases energy, indicating it is an exothermic reaction. This process is part of cellular respiration, where energy is harnessed for biological functions.

During a lab activity, students prepared two solutions separately at the same temperature. Later they mixed the solutions and the temperature dropped. Why?

• There was no energy input during the chemical reaction.

• Energy was absorbed during the chemical reaction.

• Energy was released during the chemical reaction.

• The temperature of the surroundings dropped.

Answer explanation

The temperature dropped because energy was absorbed during the mixing of the solutions, indicating an endothermic reaction. This absorption of energy from the surroundings leads to a decrease in temperature.

Why is respiration an exothermic reaction?

• A large amount of energy is released into the surroundings.

• The heat content, q, of the reaction is positive.

• A large amount of energy is required to activate the reaction.

• There is no exchange of energy between the system and the surrounding.

Answer explanation

Respiration is an exothermic reaction because it releases a large amount of energy into the surroundings as glucose is broken down. This energy release is a key characteristic of exothermic processes.

Match the following types of reactions with their characteristics.

• Proceeds only in one direction.

• reversible

• Can proceed in both forward and backward directions.

• endothermic

• Heat is absorbed from the surroundings.

• irreversible

• Heat is released to the surroundings.

• exothermic

Match the following components with their heat content in an endothermic reaction.

• Lower heat content

• reaction vessel

• Contains the reaction

• reactants

• Common solvent

• water

• Higher heat content

• products

In an experiment, Ann mixes concentrated sulfuric acid with water in a reaction test tube. The walls of the test tube turn hot. What type of reaction has occurred?

• endothermic

• exothermic

• reversible

• irreversible

Answer explanation

The reaction between concentrated sulfuric acid and water is exothermic, as it releases heat, causing the test tube to become hot. This indicates that energy is being released to the surroundings.

On top, label each graph as exothermic or endothermic reaction. On bottom, label as an example steel wool or NH₄Cl + H2O + heat ---> NH₄+ + Cl-.

a

b

c

d

NH₄Cl + H2O + heat ---> NH₄+ + Cl-

Endothermic Reaction

Steel Wool Combustion

Exothermic Reaction