Determining The Latent Heat Of Vaporisation Of Nitrogen Essay
The aim of this experiment was to determine the latent heat of vaporisation of nitrogen. To do this, a resistor connected to a power supply was used to heat up liquid nitrogen. Measuring the current and resistance in the circuit gave the power supplied to the liquid nitrogen and measuring how long it took for a fixed amount of nitrogen gas to be produced gave the rate of evolution of nitrogen gas. Plotting the power against the rate of evolution and determining the gradient yielded the value of 188 ± 22 kJkg¯¹ for the latent heat of vaporisation of nitrogen. This is within the accepted value of 199 kJkg¯¹  but the uncertainty is very large which could have been minimised through minimizing sources of random errors. Also the measured value is offset from the accepted value by 11kJkg¯¹ which suggests systematic error. The sources of these errors and how they might be minimized in the future are addressed later in the report.
The latent heat of vaporisation, Lv, is the energy required per unit mass for a liquid to change into a gas without increasing its temperature ( page 596 ). The energy required to vaporise a liquid is therefore given by:
Q = mLv (1) where Q is the energy required and m is the mass of the substance that has been vaporised.
If we supply power, P, to the liquid over a time, t, then the energy supplied to it is Q = Pt. Also, we can write the mass of the…