BRAINCAKEFlame Calorimeter
A flame calorimeter is an improved apparatus for measuring enthalpies of combustion. It is designed to reduce the large heat losses that occur when a spirit burner heats a beaker or copper can of water.
The fuel is burnt in a small enclosed burner supplied with pure oxygen rather than air. This makes combustion more complete, so less soot and carbon monoxide are formed.
The hot gases from the flame are drawn up through a long spiral copper chimney that passes through a known mass of water. The spiral gives a large surface area and a long path, so most of the heat from the gases is transferred to the water. The water is stirred and the apparatus is insulated.
The mass of fuel burnt is found by weighing the burner before and after, and the temperature rise of the water is measured. The heat released is calculated using q = mcΔT and divided by the moles of fuel burnt to give ΔcH.
Some heat is still absorbed by the apparatus itself, so the calorimeter is often calibrated first by burning a substance with a known enthalpy of combustion. Results are much closer to data book values than those from a simple calorimeter.