7.2.1 Exothermic and Endothermic Reactions

• What are exothermic reactions?

  Chemical reactions that release energy
• How do exothermic reactions affect the surroundings?

  They increase the temperature of the surroundings
• What happens when an acid and a base are mixed?

  Heat is released during the reaction
• How do endothermic reactions affect their surroundings?

  They cause the temperature to decrease
• What is the sign of ∆H in endothermic reactions?

  Positive (+)
• What is released during burning fuels?

  Heat and light
• What are the key differences between endothermic and exothermic reactions?

  • Endothermic: absorb energy; exothermic: release energy
  • Endothermic: surroundings' temperature decreases; exothermic: increases
• What are endothermic reactions?

  Chemical reactions that absorb energy
• How can the energy changes in endothermic and exothermic reactions be used to determine the direction of the reaction?

  • If the energy of the products is higher than the energy of the reactants, the reaction is endothermic and the direction of the reaction is from left to right.
  • If the energy of the products is lower than the energy of the reactants, the reaction is exothermic and the direction of the reaction is from right to left.
• What is the difference between an endothermic and exothermic reaction?

  • Endothermic reactions absorb energy, while exothermic reactions release energy.
  • The energy of the products is higher than the energy of the reactants in endothermic reactions, while the opposite is true for exothermic reactions.
• What is the relationship between the direction of reaction and the energy changes in endothermic and exothermic reactions?

  • In endothermic reactions, the direction of the reaction is from left to right, with the energy of the products being higher than the energy of the reactants.
  • In exothermic reactions, the direction of the reaction is from right to left, with the energy of the products being lower than the energy of the reactants.
• What is the energy change in endothermic reactions?

  • Absorb energy from surroundings
  • Positive change in enthalpy (∆H)
• What is the direction of the reaction in an endothermic process?

  From left to right
• If a reaction has a higher energy of products compared to the energy of reactants, what type of reaction is it?

  Endothermic
• Why is the energy of the products lower than the energy of the reactants in an exothermic reaction?

  Because the reaction releases energy to the surroundings
• Why is the energy of the products higher than the energy of the reactants in an endothermic reaction?

  Because the reaction absorbs energy from the surroundings
• What is the direction of the reaction in an exothermic process?

  From right to left
• In exothermic reactions, where do the products stand in relation to the reactants in terms of energy?

  Products are lower in energy than reactants
• What is the name of the type of chemical reaction shown on the right side of the image?

  Endothermic reaction
• What is the name of the type of chemical reaction shown on the left side of the image?

  Exothermic reaction
• How do endothermic reactions differ from exothermic reactions regarding energy levels?

  Endothermic reactions have higher energy products
• What is required to initiate both exothermic and endothermic reactions?

  Activation energy
• How do the energy profiles of endothermic and exothermic reactions differ in terms of activation energy and energy of products?

  • In endothermic reactions, the activation energy is higher than the energy of the products, while in exothermic reactions, the activation energy is lower than the energy of the products.
  • The energy of the products is higher than the energy of the reactants in endothermic reactions, while the opposite is true for exothermic reactions.
• What is the activation energy in an endothermic reaction?

  The activation energy is the energy required to start the reaction.
• What is the activation energy in an exothermic reaction?

  The activation energy is the energy required to start the reaction.
• How does the enthalpy change differ between exothermic and endothermic reactions?

  • In exothermic reactions, the enthalpy change is negative (heat is released).
  • In endothermic reactions, the enthalpy change is positive (heat is absorbed).
• How does the progress of the reaction differ between exothermic and endothermic reactions?

  • In exothermic reactions, the progress of the reaction moves from reactants to products.
  • In endothermic reactions, the progress of the reaction moves from reactants to activation energy to products.
• What do energy diagrams illustrate in chemical reactions?

  Energy changes during chemical reactions
• What does the sign of $\Delta H$ indicate?


  It indicates energy flow direction
• What happens to energy in exothermic reactions?

  Energy is released from reactants to products
• How do the enthalpy changes differ between exothermic and endothermic reactions?

  In exothermic reactions, the enthalpy change is negative, while in endothermic reactions, the enthalpy change is positive
• What is the sign of $\Delta H$ in exothermic reactions?


  Negative
• What is the relationship between the reactants and the products in an endothermic reaction?

  The products have higher enthalpy than the reactants
• What are the key features that differentiate exothermic and endothermic reactions?

  • Exothermic:
  • Energy of Products: Lower
  • Energy Change: Releases energy
  • Surroundings Effect: Warms up
  • Endothermic:
  • Energy of Products: Higher
  • Energy Change: Absorbs energy
  • Surroundings Effect: Cools down
• What occurs in endothermic reactions regarding energy?

  Energy is absorbed as products gain energy
• What is the relationship between the reactants and the products in an exothermic reaction?

  The products have lower enthalpy than the reactants
• If an exothermic reaction releases $300 \text{kJ}$, what is $\Delta H$?


  $-300 \text{kJ}$
• What is the difference between an endothermic and exothermic reaction?

  • Endothermic reactions absorb energy, while exothermic reactions release energy.
  • The energy of the products is higher than the energy of the reactants in endothermic reactions, while the opposite is true for exothermic reactions.
• How does the sign of $\Delta H$ reflect energy flow in a system?


  Negative indicates energy leaving, positive entering
• What is the direction of the reaction in an exothermic process?

  From right to left