5.1 Exothermic and endothermic reactions

• Exothermic reactions have a negative enthalpy change (ΔH < 0).

  True
• What is an endothermic reaction?

  Absorbs energy from surroundings
• What happens to the temperature of the surroundings during an endothermic reaction?

  Decreases
• In an exothermic reaction energy profile diagram, what is the relative energy level of the products compared to the reactants?

  Lower
• In an endothermic reaction, the reactants have a lower energy
• Match the reaction type with its property:

  Exothermic Reaction ↔️ Energy is released

  Endothermic Reaction ↔️ Energy is absorbed
• Endothermic reactions cause the temperature of the surroundings to increase.

  False
• The height of the peak on an energy profile diagram represents the activation energy.
• In exothermic reactions, the reactants start at a higher energy level
• For exothermic reactions, ΔH represents the difference in energy between reactants and products
• In endothermic reactions, which has a higher energy level: reactants or products?

  Products
• What happens to the temperature of the surroundings in an endothermic reaction?

  Decreases
• What type of energy is absorbed in photosynthesis, an example of an endothermic reaction?

  Light energy
• What is an exothermic reaction?

  Releases energy to surroundings
• What happens to the temperature of the surroundings during an exothermic reaction?

  Increases
• In endothermic reactions, energy is absorbed from the surroundings, causing the temperature to decrease
• Arrange the key features of an exothermic reaction energy profile diagram:

  1️⃣ Reactants at higher energy level

  2️⃣ Transition state at peak energy

  3️⃣ Products at lower energy level

  4️⃣ Negative enthalpy change (ΔH < 0)
• In an exothermic reaction, the reactants have a higher energy
• The energy change (ΔH) for an endothermic reaction is positive
• In an exothermic reaction, energy is released to the surroundings
• Match the reaction type with an example:

  Exothermic ↔️ Combustion of methane

  Endothermic ↔️ Photosynthesis
• The enthalpy change (ΔH) for exothermic reactions is positive.

  False
• Activation energy corresponds to the height of the peak on the energy profile diagram.


  True
• The transition state is the point of highest energy in the reaction pathway.


  True
• The energy change (ΔH) is positive for endothermic reactions.
• Combustion is an example of an exothermic reaction that releases heat and light.
• Melting ice is an endothermic process that absorbs heat to change into water.
• In exothermic reactions, energy is often released in the form of heat
• Match the type of reaction with an example:

  Exothermic ↔️ Combustion

  Endothermic ↔️ Photosynthesis
• Endothermic reactions have a positive enthalpy change (ΔH > 0).

  True
• The enthalpy change (ΔH) for an exothermic reaction is always negative
• The energy change (ΔH) for an exothermic reaction is negative
• The energy profile diagram for an endothermic reaction is downward-sloping.

  False
• Exothermic reactions increase the temperature of the surroundings
• In an endothermic reaction, energy is absorbed from the surroundings
• What do energy profile diagrams visualize?

  Energy changes during reactions
• What is the sign of ΔH for exothermic reactions?

  Negative
• What is the shape of the energy profile diagram for an exothermic reaction?

  Downward-sloping
• The energy profile diagram for an endothermic reaction has an upward-sloping shape.


  True
• Respiration is an exothermic reaction that maintains body temperature.


  True