All

• What happens to bonds during a reaction?

  Bonds are broken and then made
• What is required for bonds to be broken?

  Energy is taken in from surroundings

  
• What occurs when bonds are formed?

  Energy is given out
• How does the overall energy change of a reaction depend on bond processes?

  It depends on energy transferred in breaking and forming bonds

  
• What is the enthalpy change when energy is taken in?

  Enthalpy change is positive

  
• What is the enthalpy change when energy is released?

  Enthalpy change is negative

  
• Under what conditions is enthalpy measured?

  100 kPa pressure and 298 K temperature
• What is the enthalpy of formation (∆​f​H​o​)?

  Enthalpy change when one mole of substance is produced from elements

  
• What is the enthalpy of combustion (∆​c​H​o​)?

  Enthalpy change when one mole of substance is burned in oxygen

  
• What do mean bond enthalpies represent?

  Energy required to break different covalent bonds

  
• How are bond enthalpy values determined?

  Using calorimetry methods experimentally

  
• Why do bond enthalpy values differ from data book values?

  They are not exact and vary in each situation
• What is calorimetry?

  Experimental method for finding enthalpy change
• What does calorimetry measure to find enthalpy change?

  Temperature change over time
• How is the measured change in temperature related to energy change?

  It is proportional to the energy change
• What is the formula for calculating energy change (q)?

  q = mc∆T

  
• What is specific heat capacity?

  Energy required to raise 1g of substance by 1K
• Why are ∆H values found using calorimetry never completely accurate?

  Energy is lost through conduction or convection
• What does Hess's Law state about energy in a reaction system?

  Energy must be conserved
• What does Hess's Law allow us to determine?

  Enthalpy changes for reactions not found directly
• What method is used in Hess's Law to calculate enthalpy changes?

  Triangular cycle method with an intermediate product
• How do the arrows in Hess's Law diagrams indicate calculations?

  They indicate whether to add or subtract values
• How can Hess's Law be used with enthalpies of formation?

  To calculate enthalpy change using given enthalpies

  
• What do the arrows point to in the triangular diagram for enthalpies of formation?

  Arrows point out from the central product
• How can Hess's Law be used with enthalpies of combustion?

  To calculate enthalpy change using combustion enthalpies
• What do the arrows point to in the triangular diagram for enthalpies of combustion?

  Arrows point towards the central product
• What do bond enthalpy data represent?

  Energy required to break one mole of bond

  
• How can bond enthalpy data be used with Hess's Law?

  To find overall enthalpy change for a reaction

  
• What direction do reaction arrows point in Hess's Law diagrams?

  Arrows point towards the central product
• What energy change is associated with breaking bonds?

  Energy is taken in to break bonds
• What type of reaction is associated with breaking bonds?

  Endothermic reaction
• What energy change is associated with making bonds?

  Energy is released to make bonds
• What type of reaction is associated with making bonds?

  Exothermic reaction
• What are some uses of thermochemistry?

  • Measuring energy values of fuels
  • Calculating energy requirements for processes
  • Working out theoretical energy changes in reactions
  • Predicting if a reaction will occur
• What is an endothermic reaction?

  Overall positive enthalpy change (+ΔH)
• What does an endothermic reaction indicate about energy?

  Energy in breaking bonds > energy out making bonds

  
• What is an exothermic reaction?

  Overall negative enthalpy change (-ΔH)
• What does an exothermic reaction indicate about energy?

  Energy in breaking bonds < energy out making bonds

  
• If a reversible reaction is endothermic one way, what type is the other way?

  Exothermic
• What is enthalpy change represented by?

  ΔH