7.2 Energy Changes

• An endothermic reaction absorbs energy from the surroundings in the form of heat
• An exothermic reaction releases energy to the surroundings in the form of heat.

  True
• Exothermic reactions cause the temperature of the surroundings to increase.


  True
• Order the following examples of energy changes in chemical reactions based on whether they are endothermic or exothermic:

  1️⃣ Melting ice (endothermic)

  2️⃣ Photosynthesis (endothermic)

  3️⃣ Burning fuels (exothermic)

  4️⃣ Neutralization reactions (exothermic)
• Activation energy is the minimum energy required to initiate a chemical reaction
• Activation energy acts as an energy barrier that reactants must overcome to form products.

  True
• Endothermic reactions have higher activation energies compared to exothermic reactions.
• Exothermic reactions have lower activation energies because they release energy.
• What happens to activation energy in endothermic reactions as they absorb energy?

  It increases
• Exothermic reactions have lower activation energies because they release energy
• Activation energy is the threshold energy needed to start a chemical reaction
• Why do endothermic reactions have higher activation energies?

  They absorb energy
• Match the type of reaction with its activation energy requirement:

  Endothermic ↔️ High activation energy

  Exothermic ↔️ Low activation energy
• What happens to the energy of reactants in an exothermic reaction compared to the products?

  Reactants have higher energy
• Order the steps shown in an endothermic reaction energy diagram

  1️⃣ Products are at a higher energy level

  2️⃣ Energy is absorbed during the reaction

  3️⃣ Activation energy is overcome

  4️⃣ Reactants transform into products
• Exothermic reactions release energy, whereas endothermic reactions absorb energy.


  True
• An exothermic reaction releases energy to the surroundings.
• In an exothermic reaction energy diagram, what is the relative energy level of reactants compared to products?

  Reactants are higher
• For exothermic reactions, the reactants have higher energy
• In endothermic reactions, what type of energy change occurs?

  Energy is absorbed
• Endothermic reactions cause the temperature of the surroundings to decrease

  True
• What happens to the temperature in the surroundings during an exothermic reaction?

  Increases
• What type of reaction requires higher activation energy: exothermic or endothermic?

  Endothermic
• Exothermic reactions have lower activation energy compared to endothermic reactions

  True
• Steps of energy change in an endothermic reaction

  1️⃣ Reactants at initial energy level

  2️⃣ Energy is absorbed from surroundings

  3️⃣ Products at higher energy level
• What is the energy relationship between reactants and products in an exothermic reaction?

  Reactants have higher energy
• The activation energy required for exothermic reactions is higher compared to endothermic reactions.

  False
• In an endothermic reaction, the products have higher energy than the reactants.
• Factors influencing activation energy in order of increasing complexity:

  1️⃣ Nature of Reactants

  2️⃣ Catalyst Presence

  3️⃣ Temperature
• A catalyst lowers activation energy by providing an alternate pathway.
• What is the fundamental principle of Hess's Law?

  Enthalpy change is path-independent
• Steps in applying Hess's Law:

  1️⃣ Identify the overall reaction

  2️⃣ Break down into steps with known ΔH

  3️⃣ Add up the enthalpy changes
• The enthalpy change for the first step in the Hess's Law example is -167 kJ/mol.

  True
• Match the property with its description for endothermic and exothermic reactions:

  Energy Change in Endothermic ↔️ Absorbs energy from surroundings

  Temperature Change in Exothermic ↔️ Increases temperature of surroundings
• In an endothermic reaction, the surroundings experience a decrease in temperature
• What is the definition of activation energy?

  Threshold energy to start a reaction
• Activation energy is the minimum energy required to initiate a chemical reaction.


  True
• Steps involved in the role of activation energy in a reaction

  1️⃣ Reactants absorb energy

  2️⃣ Bonds in reactants break

  3️⃣ Reactants reach transition state

  4️⃣ New bonds form to create products
• Exothermic reactions release energy, resulting in lower activation energies.
• Exothermic reactions release energy, while endothermic reactions absorb energy.


  True