1- thermochemistry

• What are the two types of heat changes in chemical reactions?

  Exothermic and endothermic
• What happens during an exothermic reaction?

  Heat is released to the surroundings
• What is chemical energy a form of?

  Potential energy
• What is enthalpy, H?

  Heat energy exchanged in a chemical reaction
• What is the symbol for change in enthalpy?

  ΔH
• What are the units for enthalpy?

  Joules (J) or kilojoules (kJ)
• How is the change in enthalpy calculated?

  ΔH = Hproducts - Hreactants
• What does a negative ΔH indicate?

  Exothermic reaction
• What does a positive ΔH indicate?

  Endothermic reaction
• What are the standard conditions for measuring enthalpy changes?

  • All substances in standard states
  • Temperature of 298K (25°C)
  • Pressure of 1 atmosphere (101,000 Pa)
• What is the standard enthalpy change of formation?

  Enthalpy change when one mole forms from elements
• What is the standard enthalpy change of combustion?

  Enthalpy change when one mole combusts in oxygen
• What is the symbol for standard enthalpy change of combustion?

  ΔH
• How is the standard enthalpy change of reaction calculated?

  From standard enthalpies of formation of reactants/products
• What is the equation for calculating standard enthalpy change of reaction?

  ΔH = ΣΔH(products) - ΣΔH(reactants)
• What is the standard enthalpy change of reaction for 2H2S(g) + SO2(g) → 3S(s) + 2H2O(l)?

  -234.6 kJ mol⁻¹
• What does Hess's Law state?

  Total enthalpy change is independent of the route
• How do you calculate the enthalpy change using Hess's Law?

  ΔH = A - B
• What is the enthalpy change of combustion for ethane?

  -1560 kJ mol⁻¹
• What is bond enthalpy?

  Energy needed to break a covalent bond
• What is average bond enthalpy?

  Average energy required to break a bond type
• What is the first step in bond energy calculations?

  Draw out the molecule to see the bonds
• What is the equation for calculating enthalpy change using bond energies?

  ΔH = Σ(bonds broken) + Σ(bonds formed)
• What is the enthalpy change for the hydration of ethene?

  -1134 kJ mol⁻¹
• What does the equation q = mcΔT represent?

  Heat transferred in a reaction
• How do you calculate the enthalpy change per mole?

  ΔH = -q / n
• What is the enthalpy change for the reaction of magnesium with copper sulfate?

  151.7 kJ mol⁻¹
• What are the key considerations for practical investigations in enthalpy changes?

  • Accurately measure liquids with a burette
  • Ensure good insulation to minimize energy loss
  • Use a bomb calorimeter for accurate combustion values
• Why is the experimental value for enthalpy change usually less than the book value?

  Energy lost to surroundings