Determination of enthalpy change of combustion

Question 1

WHat does a caloromiter contain? How is heat loss reduced?

Answer 1

contains water

insulated

Question 2

WHat is the method?

Answer 2

• accurately measured 100cm3 of water into a calorimeter
• weigh a spirit burner container the liquid to be burnt
• measure intitail temperature
• use spirit burner to heat water
• stop heating when there is a significant rise around 15 degrees
• reweigh spirit burner

Question 3

How is the enthalpy of combustion worked out?

Answer 3

• measure change in temperature
• use q = mc T
• calc mass of fueld used in burner
• calc moles of fuel burnt
• energy change / moles

Question 4

Why is the vlaue of the enthalpy of combustioned determined experimentall is frequently less exothermic than the value found in data book?

Answer 4

• heat loss to surrounding from the spirit burner, wick, and calorimiter
  
  • flame affected by draughts
• loss of fuel from wick or burner by evaporation
• loss of water by evaporatrion
• incomplete combustion
  
  • leaving soot on bottom of calorimiter
• heat used to raise temp of calorimiter
• unlikely to occur under standard condition

Question 5

How is accuracy of values improves?

Answer 5

• using a draught shield to redcude heat loss
• lid on calorimiter to reduce heat loss
• minimise distance between the flame and the calorimiter
• insulating the calorimiter and the spirit burner to reduce heat loss
• using a top on the spirit burner with wick protuding to reduce evaporation
• burn in a supply of pure oxygen to prevent incomplete combustion