Thermochemistry

• What fuel does a typical laboratory Bunsen burner use?

  Natural gas
• What is the main component of natural gas?


  Methane, CH4
• What do methane and oxygen produce when they react?

  Carbon dioxide and water
• What does a chemical equation indicate about a reaction?

  It shows the reactants and products
• What is needed to show the energy change in a reaction?

  An energy level diagram (enthalpy level diagram)
• In a reaction, which contains more energy: the reactants or the products?

  The reactants contain more energy
• What symbol is used to denote the change in enthalpy?

  ΔH
• What type of reaction is the combustion of methane?

  Exothermic reaction
• What happens to energy in an exothermic reaction?

  Energy is released to the surroundings
• In an endothermic reaction, how do the enthalpy levels of reactants and products compare?

  The reactants are at a lower enthalpy level than the products
• What is the thermal decomposition of calcium carbonate an example of?

  An endothermic reaction
• What does a positive ΔH indicate?

  Energy is taken in from the surroundings
• What are the main differences between exothermic and endothermic reactions?

  • Exothermic:
  • Releases energy
  • Enthalpy of the system decreases
  • Endothermic:
  • Absorbs energy
  • Enthalpy of the system increases
• What is the system when studying enthalpy changes in reactions?

  The reactants and products
• What are the surroundings in an enthalpy change experiment?

  Everything else, including the bench top, air, and equipment
• What does the symbol ΔH_θ represent?

  An enthalpy change under standard conditions
• How do you convert from °C to K?

  Add 273
• What is the standard state of H2O

  Liquid
• What is the standard enthalpy of formation of an element in its standard state?

  Zero
• What is the standard state of hydrogen, H2O

  Gas
• What is the standard state of oxygen, O2

  Gas
• What do hydrogen and oxygen react to form?

  Water
• What is the equation for the enthalpy of formation of water?

  H2> + 0.5 O2> → H2O
• Can enthalpies of formation be negative?

  Yes, they can be negative or positive
• What is the standard enthalpy of combustion?

  The enthalpy change when 1 mole of a substance is competely burned in oxygen under standard conditions
• What is calorimetry used for?

  To measure the enthalpy change of a reaction
• What must be known to measure the enthalpy change using calorimetry?

  A known amount of water
• What is needed to mix the warm and cold water evenly in calorimetry?

  A stirrer
• What should be recorded at the start and end of a calorimetry experiment?

  The temperature
• What is the purpose of the spirit burner in the experiment?


  To contain the liquid fuel
• Why is it a good idea to use screens during the experiment?


  To stop draughts
• What should be done after lighting the wick in the calorimetry experiment?


  Stir carefully as the water warms up
• How is the mass of fuel burned calculated?

  By re-weighing the burner, lid, and fuel
• What is the change in temperature calculated from?

  The difference between the starting and ending temperatures
• How is the heat gained by the water calculated?

  Using the equation $q =$$mc\Delta T$
• What does $q$ represent in the equation $q =$$mc\Delta T$?


  Energy transferred to the water, J
• What does $m$ represent in the equation $q =$$mc\Delta T$?


  Mass of the water, g
• What does $c$ represent in the equation $q =$$mc\Delta T$?


  Specific heat capacity of water (4.18 J g)
• What does $\Delta T$ represent in the equation $q =$$mc\Delta T$?


  Temperature change, K
• How do you calculate the number of moles of fuel burned?

  Using the formula $\text{Moles} =$$\frac{\text{mass}}{\text{Mr}}$