why must calorimeter be calibrated?

[nothingsus]

Could someone elaborate on this? I think i heard that it has something to do with the fact that all calorimeters are slightly different.

[vox nihili]

That's pretty much it. It's because the calorimeters are different, so the amount of heat lost to the environment is different. Calibrating them takes this difference in heat loss into account, thus ensuring that the calculations are based entirely on the substance being tested.

[PB]

It also takes into account the conditions on that day, because you may not always be able to simulate Standard Laboratory Conditions, which can alter the Specific Heat Capacity of the water perhaps.
Thus, when you calibrate it by putting into a known amount of energy and noting the subsequent rise of temperature, you can calculate the calibration factor (C=E/T)
Which is an important component of the formula (E=CT) which you can use to find Ethanol's Heat of Combustion, lets say.
*Heat of combustion is the enthalpy change when a mass of substance combusts entirely)