Understanding Exothermic and Endothermic Reactions

What is the key concept to understand about energy in chemical reactions?

• Energy is created during reactions.

• Energy is destroyed in chemical reactions.

• Energy is stored in the bonds of chemicals.

• Energy is irrelevant in chemical reactions.

In a reaction profile, what does the y-axis represent?

• The temperature of the reaction

• The number of molecules

• The total energy of the molecules

• The speed of the reaction

In a reaction profile, what does the x-axis represent?

• The volume of the reaction

• The pressure of the reaction

• The temperature of the reaction

• The progress of the reaction

What is a common characteristic of exothermic reactions?

• They do not involve energy transfer.

• They require no activation energy.

• They absorb energy from the surroundings.

• They release energy to the surroundings.

Which of the following is an example of an exothermic reaction?

• Evaporation of water

• Melting of ice

• Combustion of fuels

• Photosynthesis

What happens to the energy level of products in an endothermic reaction compared to reactants?

• It increases.

• It remains the same.

• It decreases.

• It fluctuates randomly.

Which of the following reactions is endothermic?

• Decomposition of calcium carbonate

• Oxidation of metals

• Neutralization of an acid and base

• Combustion of methane

What is activation energy?

• The energy required to stop a reaction

• The energy needed to start a reaction

• The energy released during a reaction

• The energy stored in products

How is activation energy represented in a reaction profile?

• As the lowest point on the curve

• As the highest point on the curve

• As the difference between reactants and products

• As a flat line

What happens to the activation energy if the curve on a reaction profile is higher?

• It remains the same

• It becomes zero

• It increases

• It decreases