Latent Heat Of Nitrogen Lab Report

Determining the Latent Heat of Vaporisation of Nitrogen

Abstract
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 [1] but the uncertainty is very large which could have been minimised
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Heat transfer from the wire would be reduced by reducing the resistance of the wires which was discussed previously so the same techniques would work (increasing resistivity and thickness of wire).
It is important to reduce these uncertainties in V, t, I and R as they affect the uncertainty of the gradient of the graph in figure 3 and therefore, the measurement of the latent heat of vaporisation.

Conclusion The aim of this experiment was to determine the latent heat of vaporisation of nitrogen. This was done by heating liquid nitrogen with a resistor and relating the power transfer to the latent heat of vaporisation. The experiment yielded a value of 188 ± 22 kJkg¯¹. This is within the accepted value of 199 kJkg¯¹ [1] but it has a large uncertainty and shows systematic error. Ways of reducing this uncertainty have been suggested including using a high frame rate camera to reduce systematic error and using a larger measuring cylinder so we can time how long it takes to produce a larger volume of gas to reduce random error. These equipment were unavailable during the experiment.
References
[1] G. W. C. Kaye and T. H. Laby, Tables of Physical and Chemical Constants: 15th

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