Question

What are the theoretical error resources for heat combustion experiment of naphthalene? (Hint: consider two major factors when derive ΔH from ΔU: first, what gas law is assumed? Second, what temperature is assumed?)

Answer 1

There are small differences (a few thousandths of a degree) in the apparent temperature rise, depending on one’s choice of time for the measurement. The elaborate theory says that the time for the calculation of the correct ∆T (to account for heat transfer problems) is the time when the area between the experimental T vs. time curve and the extrapolated upper curve is equal to the area between the experimental T vs. time curve and the extrapolated lower curve. The empirical Parr method says that the correct temperature rise, ∆Tcorr, is measured at the time when the temperature has increased to 60 % of the maximum value. {This value is NOT the same as 60% of the maximum temperature rise.}