Calculating Heats of Formation

Calculation of heats of formation with group increments

Abstract

For this report an experiment will be done to derive a model to determine the heat of formation for any alkane. Using known results gathered from online sources a model was derived using the LINEST function found on Microsoft Excel. The derived model was not extremely accurate owing to lack of sufficient chosen data. The model however can be used to obtain an estimated value for the heat of formation for any alkane.

Introduction

The heat of formation, denoted by ΔH0f, of a substance is defined as the amount of heat involved in the process of forming one mol of the substance from its elements. The elements involved have to be in their natural state and at standard pressure. For this report I will investigate the heat of formation for alkanes and through the process of multiple linear regression I want to be able to derive an expression that can be used to predict the heat of formation for any alkane. This model would be made up by different heat increments. The aim of this experiment is to use a suitable program, such as Microsoft Excel, to determine these increments and finally the entire model. The model will provide constants for the following equation:

ΔH0f (C2H2n+2) = n1ΔH0f (CH3) + n2ΔH0f (CH2) + n3ΔH0f (CH) + n4ΔH0f (C) + K (eq. 1)

Where K is some unknown constant

For the experiment I plan to use the LINEST function on Microsoft Excel and I will include a list of alkanes I chose for my data. My prediction is that ΔH0f would become more negative as the total amount of Carbon atoms in the alkane increases.

Results

According to the website of the National Institute of Standards and Technology, also known as NIST, (National Institute of Standards and Technology 2011) the following data is accurate.

Table 1. The Collected heats of formation for different alkanes as well as the carbon groups in the alkane

Alkane | Formula | CH3 | CH2 | CH | C | Collected Heat of formation (kJ/mol) |...