Kes notes chapter 9

• What is enthalpy denoted by?

  H
• What does enthalpy change measure?

  Heat energy change at constant pressure
• Under what conditions are enthalpy change values usually given?

  Standard conditions
• What are standard enthalpy changes denoted by?

  ΔH^ϴ

  
• What is the standard enthalpy change of reaction (ΔHr^ϴ)?

  Enthalpy change for a reaction at standard conditions

  
• What does the standard enthalpy of formation (ΔfH^ϴ) represent?

  Enthalpy change when one mole forms from elements

  
• What is the standard enthalpy of combustion (ΔcH^ϴ)?

  Enthalpy change when one mole burns in oxygen

  
• What does the standard enthalpy change of neutralisation (ΔneutH^ϴ) measure?

  Energy change when an acid reacts with a base

  
• What happens to the surroundings in exothermic reactions?

  Temperature increases
• What is the sign of ΔH in exothermic reactions?

  Negative
• What happens to the surroundings in endothermic reactions?

  Temperature decreases
• What is the sign of ΔH in endothermic reactions?

  Positive
• What is activation energy?

  Minimum energy required for a reaction
• What is average bond enthalpy?

  Energy to break one mole of a bond
• Why is an average bond enthalpy used?

  Bond strength varies in different environments
• What is actual bond enthalpy specific to?

  Each individual molecule
• What type of process is bond breaking?

  Endothermic
• What type of process is bond making?

  Exothermic
• How can enthalpy change be predicted?

  Using bond enthalpies

  
• How accurate are enthalpy change values from bond enthalpies?

  Approximate and less accurate than Hess’ Law

  
• What is calorimetry?

  Measuring heat change during a reaction
• What does the formula q = mcΔT represent?

  Heat change in a substance
• What does 'q' represent in the calorimetry formula?

  Heat change (J)
• What does 'm' represent in the calorimetry formula?

  Mass of the substance (g)
• What does 'c' represent in the calorimetry formula?

  Specific heat capacity (J g^-1 K^-1)
• What does 'ΔT' represent in the calorimetry formula?

  Temperature change (K or °C)
• What is the procedure for coffee cup calorimetry?

  • Place reaction mixture in Styrofoam cup
  • Insulate with lid and stirrer
  • Add first reactant and record stable temperature
  • Add second reactant and stir, measuring temperature every minute
  • Plot temperature vs. time graph
  • Calculate q using ΔT and densities
• What is the procedure for spirit burner calorimetry?

  • Place water in beaker with thermometer
  • Weigh spirit burner with fuel
  • Measure initial temperature of water
  • Burn spirit burner and stir water
  • Extinguish flame and reweigh spirit burner
  • Measure final temperature of water
  • Calculate q using measured values
• What does Hess's Law state?

  Enthalpy change is independent of the reaction route

  
• How can enthalpy changes of combustion be used?

  To find enthalpy change of a reaction

  
• How can enthalpy changes of formation be used?

  To find enthalpy change of a reaction

  
• What occurs during an enthalpy change?

  Energy is transferred between system and surroundings
• What is the enthalpy of formation for an element?

  0 kJ mol-1
• What is the system in an enthalpy change?

  The system is the chemicals involved
• What happens in an exothermic change?

  Energy is transferred from system to surroundings
• What is the sign of ∆H in an exothermic reaction?

  Negative
• What occurs in an endothermic change?

  Energy is transferred from surroundings to system
• What is the sign of ∆H in an endothermic reaction?

  Positive
• What are common exothermic processes?

  • Combustion of fuels
  • Oxidation of carbohydrates (e.g., glucose in respiration)
• What is Activation Energy (EA)?

  Minimum energy needed for particles to collide