C5

• What happens to energy during chemical reactions?

  Energy changes occur, heating or cooling
• What does it mean if products store more energy than reactants?

  They absorbed energy from surroundings
• What happens if products store less energy than reactants?

  Excess energy is released to surroundings
• What is the law of conservation of energy?

  Energy cannot be created or destroyed
• What is an exothermic reaction?

  It transfers energy to surroundings, heating
• What type of reaction is neutralization?

  Exothermic reaction
• What happens when sodium is added to water?

  It releases energy, indicating exothermicity
• How are hand warmers designed to work?

  They use exothermic oxidation of iron
• What is an endothermic reaction?

  It takes in energy from surroundings, cooling
• What is thermal decomposition?

  Heating causes substances to break down
• How are endothermic reactions used in sports injury packs?

  They cool instantly without a freezer
• What does "exo" mean in exothermic?

  Exit
• What does "thermic" refer to in exothermic reactions?

  Heat
• How can energy transfer be measured in reactions?

  By measuring temperature changes in solutions
• What is a common problem when measuring energy in reactions?

  Energy loss to surroundings
• How can insulation improve energy measurement accuracy?

  It reduces energy loss to surroundings
• What is the procedure for measuring energy in a neutralization reaction?

  Mix reactants in a polystyrene cup
• What does a reaction profile diagram show?

  Relative energies of reactants and products
• What does the initial rise in energy on a reaction profile represent?

  Activation energy needed to start reaction
• What is activation energy?

  Minimum energy needed for reactants to collide
• What happens in an exothermic reaction regarding energy?

  Particles release energy to surroundings
• What happens in an endothermic reaction regarding energy?

  Particles absorb energy from surroundings
• What is bond breaking in terms of energy?

  Endothermic process requiring energy input
• What is bond forming in terms of energy?

  Exothermic process releasing energy
• How do bond energies affect overall energy change in reactions?

  They determine energy needed to break/form bonds
• How do you calculate overall energy change for a reaction?

  Energy to break bonds minus energy to form bonds
• What is the energy change for the reaction between H₂ and Cl₂ forming HCl?

  -184 kJ/mol
• Why can't you compare overall energy changes without knowing bond energies?

  Numerical differences in bond energies matter
• What is the bond energy of H-H?

  +436 kJ/mol
• What is the bond energy of Cl-Cl?

  +242 kJ/mol
• What is the bond energy of H-Cl?

  +431 kJ/mol
• How do bond strengths affect energy changes in reactions?

  Weaker bonds require less energy to break
• What can be concluded about reactions with bromine compared to chlorine?

  Bromine bonds are weaker, affecting energy
• What is the importance of practicing bond energy calculations?

  It helps understand energy changes in reactions
• What are the key differences between exothermic and endothermic reactions?

  • Exothermic reactions release energy, causing temperature rise.
  • Endothermic reactions absorb energy, causing temperature drop.
  • Exothermic examples: combustion, neutralization.
  • Endothermic examples: thermal decomposition, citric acid reactions.
• What are the steps to measure energy changes in a neutralization reaction?

  1. Measure reactant temperatures.
  2. Mix in a polystyrene cup.
  3. Measure final temperature.
  4. Record temperature changes.
  5. Repeat with different concentrations.
• How do reaction profiles illustrate energy changes?

  • Show relative energies of reactants and products.
  • Indicate activation energy needed to start reactions.
  • Highlight energy changes during the reaction.
• What is the relationship between bond breaking and energy changes?

  • Bond breaking requires energy (endothermic).
  • Bond forming releases energy (exothermic).
  • Overall energy change depends on bond energies.
• How do you calculate overall energy change using bond energies?

  1. Sum energies needed to break bonds in reactants.
  2. Subtract energy released by forming bonds in products.
  3. Result indicates overall energy change.