Calorimetric determination of the heats of combustion of ethane, propane, normal butane, and normal pentane

The present investigation on the calorimetric determination of the heats of combustion of ethane, propane, normal butane, and normal pentane was under- taken because of the dearth of information concerning these thermochemical constants for which there is pressing need in industry and in the sciences.The data of the present investigation give for the heats evolved in the com- bustion in oxygen, at a temperature of 25 C and a constant pressure of 1 atmos- phere, of gaseous ethane, gaseous propane, gaseous normal butane, and gaseous normal pentane, respectively, to form gaseous carbon dioxide and liquid water, the following values, in international kilojoules per mole: Ethane, 1,559.57±0.44; propane, 2,219.57±0.51;normal butane, 2,877.88±0.63;normal pentane, 3,536.00±0.88.Converted to k-cali 5 by means of the factor 1.00040/4.1850,these values become, in k-cali 5 per mole: Ethane, 372.81 ±0.11; propane, 530.57±0.12; normal butane, 687.94 ±0.15; normal pentane, 845.27 ±0.21.The hitherto "best" values for the heats of combustion of these gases differ from the values obtained in the present investigation by the following amounts Ethane, -1.23 percent; propane, -0.87 percent; normal butane, no existing data; normal pentane, -0.86 percent.These differences are from 30 to 50 times the estimated uncertainties in the values from the present investigation.CONTENTS Page I. Introduction 736 II.Units, atomic weights, etc 736 III.Method and apparatus 737 IV.Chemical procedure 739 1. Preparation and purity of the hydrocarbons 739 2. Purity of the combustion reaction 741 3. Determination of the amount of reaction 742 V. Calorimetric procedure 742 1. Electrical energy experiments 742 2. Correction experiments 743 3. Reaction experiments 744 VI.Results of the present investigation 746 VII.Data of previous investigations 747 1. Ethane 747 2. Propane 747 3. Normal butane 748 4. Normal pentane