Chapter 9

• What is the enthalpy change of formation (Δ_fH)?


  Enthalpy change when one mole of a substance forms from its elements
• What is the enthalpy change of neutralisation (Δ_neutH)?

  Enthalpy change when one mole of water is formed from a neutralisation
• What is the enthalpy change of reaction (ΔrH)?

  Enthalpy change for a reaction
• What is the enthalpy change of combustion (ΔcH)?

  Enthalpy change when one mole is burnt completely in oxygen
• How is the enthalpy change of formation defined?

  It is defined for one mole formed from elements
• How does the enthalpy change of neutralisation differ from the enthalpy change of combustion?

  Neutralisation forms water, combustion burns a substance
• If one mole of a substance is completely burnt in oxygen, what is this enthalpy change called?

  Enthalpy change of combustion (ΔcH)
• What is measured to determine enthalpy changes?

  Temperature change of the surroundings
• What is the Kelvin scale's starting point?

  Absolute zero, 0 K
• What temperature does ice melt at in Kelvin?

  273 K
• How does a 1 K rise in temperature compare to a 1 °C rise?

  They are equivalent
• What is the formula for calculating energy change?

  q = mcΔT
• What does specific heat capacity measure?

  Energy to raise 1 g by 1 K
• How is temperature change ΔT calculated?

  ΔT = Tfinal – Tinitial
• Why is the experimental ΔcH value often lower than the data book value?

  Less heat is transferred to water
• What are possible reasons for discrepancies in ΔcH values?

  Heat loss, incomplete combustion, evaporation
• How can draught screens help in experiments?

  Minimize heat loss and incomplete combustion
• What is the purpose of using polystyrene foam cups in reactions?

  Insulate against heat loss
• How is temperature change measured in reactions between solutions?

  Using a thermometer in the solution
• What happens during energy transfer in solutions?

  Energy transfer occurs within the solution
• What is the significance of the specific heat capacity in experiments?

  It affects the energy change calculations
• What is the role of the thermometer in measuring energy changes?

  It records temperature changes in surroundings
• Why is it important to weigh the burner soon after the experiment?

  To minimize methanol evaporation loss
• What is the Kelvin scale of temperature?

  The Kelvin scale starts at absolute zero, 0 K, and is equivalent to -273°C
• How does the Kelvin scale relate to the Celsius scale?

  A 1 K rise in temperature is the same as a 1 °C rise in temperature
• What is the formula to calculate energy change (q)?

  q = mcΔT
• Why do good conductors of heat like metals have small values of specific heat capacity?

  They require less energy to raise their temperature by 1 K
• Why is the experimental value for the enthalpy change of combustion of methanol (-514 kJ mol^{-1}) different from the data book value (-726 kJ mol^{-1})?

  Possible reasons include heat loss to the surroundings, incomplete combustion, and evaporation of methanol
• How can errors in the enthalpy change of combustion experiment be minimized?

  Using draught screens and an input of oxygen gas could minimize errors from heat loss and incomplete combustion
• What is the purpose of using polystyrene foam cups when determining enthalpy changes of reactions?

  They minimize heat loss to the surroundings
• How does the calorimetry process work for determining enthalpy changes of reactions?

  • The reaction takes place in the solution itself
  • A thermometer in the solution records the temperature change
  • The heat energy change is calculated using q = mcΔT
• What are the strengths and weaknesses of qualitative research methods?

  Strengths:

  • Provides in-depth, rich data
  • Flexible and adaptable to new information
  • Captures complex phenomena

  
  

  Weaknesses:

  • Time-consuming and labor-intensive
  • Potential for researcher bias
  • Limited generalizability
  • Difficulty in replicating results
• What can average bond enthalpies be used for?

  To calculate enthalpy changes of reaction
• What is average bond enthalpy?

  Energy required to break one mole of bond
• Is energy required to break bonds?

  Yes, energy is always required
• What type of process is bond breaking?

  Bond breaking is endothermic
• What type of process is bond making?

  Bond making is exothermic
• What is the sign of $\Delta H_f \text{ for bond breaking}?$


  $\Delta H_f \text{ is positive}$
• What is the sign of $\Delta H_f \text{ for bond making}?$


  $\Delta H_f \text{ is negative}$
• How can the enthalpy change of reaction $\Delta H_f$ be calculated?


  By calculating bond enthalpies in reactants and products