Energetics

• What does the symbol Delta H represent?

  Enthalpy change in a reaction
• What are the standard conditions for measuring enthalpy change?

  100 kPa and 298 K
• What is an endothermic reaction?

  A reaction that absorbs energy from surroundings
• How does an endothermic reaction feel when touched?

  It feels colder to the touch
• What is the enthalpy change for the decomposition of calcium carbonate?

  +178 kJ per mole
• What is an exothermic reaction?

  A reaction that releases heat energy
• How does an exothermic reaction feel when touched?

  It feels warmer to the touch
• What is the enthalpy change for burning ethane?

  -1560 kJ per mole
• What happens to energy when bonds are broken?

  Energy is absorbed
• What is the enthalpy change when bonds are formed?

  Energy is released
• How do you determine if a reaction is endothermic or exothermic?

  By comparing energy absorbed and released
• What is mean bond enthalpy?

  Average energy required to break bonds
• Why do bond enthalpies vary in a molecule?

  Due to different environments of bonds
• How do you calculate the mean bond enthalpy of CH bonds in methane?

  Divide total energy by number of bonds
• What is the equation for calculating energy change in a reaction?

  Total energy to break bonds minus form energy
• How do you calculate the energy change for the combustion of methane?

  Use bond enthalpy data for calculations
• What is calorimetry used for?

  To measure enthalpy change of combustion
• What is the formula for calculating energy transferred in calorimetry?

  Q = mcΔT
• What does 'm' represent in the calorimetry equation?

  Mass of water or solution
• What is the specific heat capacity value used in calculations?

  4.18 J/g°C
• How do you convert energy from joules to kilojoules?

  Divide by 1000
• How do you calculate the number of moles of ethanol used?

  Mass divided by molar mass
• What is the enthalpy change of ethanol combustion calculated from the experiment?

  -364.5 kJ per mole
• What is the purpose of a polystyrene cup in calorimetry?

  To minimize heat loss to surroundings
• Why do we measure temperature before and after adding reactants in calorimetry?

  To determine the temperature change
• What type of reactions are typically used in calorimetry experiments?

  Acid-base reactions
• What is the significance of measuring temperature change in calorimetry?

  It indicates the energy transferred
• What is the formula for calculating entropy change?

  Energy divided by moles minus 14212
• Why is the entropy change negative in this context?

  Because the reaction is exothermic
• What is the entropy change of the fuel mentioned?

  -364.5 KJ per mole
• What is the purpose of a polystyrene cup in calorimetry experiments?

  • Prevents heat loss
  • Contains heat within the beaker
• What is the first step in a calorimetry experiment with a solution?

  Add the acid and measure the temperature
• Why do we typically use acid-alkali reactions in calorimetry?

  They show a reasonable temperature change
• What was the initial temperature of the HCl solution in the example?

  20° C
• How much did the temperature rise after adding sodium hydroxide?

  Raised to a maximum of 26° C
• How do you calculate the energy change in the calorimetry example?

  Use Q = MCΔT
• What mass is used in the energy change calculation?

  Mass of both liquids combined
• What is the assumed density of the liquids in the example?

  1 g per cm³
• How do you convert volume from cm³ to dm³?

  Divide by 1000
• What is the number of moles of HCl calculated in the example?

  0.0250 moles