Chemical Reactions And Exothermic Reactions

Introduction

During chemical reactions, energy is either released or absorbed, normally as either heat or light energy. There are two types of reactions that involve heat, exothermic reactions and endothermic reactions. In an exothermic reaction heat energy is released and increases the temperature of its surroundings. Conversely in an endothermic reaction heat energy is absorbed and the surrounding temperature decreases. The measurement of change in heat is called calorimetry.

The change in heat energy is known as the enthalpy change , and it is the quantity of heat released or absorbed during a reaction when 1.00 mol of a substance undergoes a chemical reaction while under constant pressure. The molar enthalpy of Combustion is the quantity

If the base of the beaker is wider, then the flame will have a greater surface area to heat through. If the glass at the base of the beaker is thicker, then there will be a greater amount of heat loss from heating the glassware.

-The alcohol burner design: If different burner designs are used, then the spread of the flame could be different. This could result in differing proportions of heat loss between samples.

In order for the hypothesis to be supported, the results would need to show a clear trend of enthalpy decreasing (as this this is a combustion reaction the enthalpy will be negative) as the molar mass of the alcohols increases as well.

Procedure:

Materials: Electronic Balance Scale, Ethanol burner, Propanol burner, Butanol burner, Pentanol burner, Hexanol burner, Tripod, Gauze mat, 2 250ml glass beakers, distilled water, thermometer, a retort stand with a clamp, tiles, matches, heat mat, and stirring rod.

Method:

1) A tripod will be set up with a gauze mat, on top of a heat mat.

2) A retort stand will be set up next to the tripod, with a clamp attached.

3) A 200mL beaker is filled with 100mL of distilled water, the beaker will then be placed on top of the

The change in temperature ( ) is 10 degrees Celsius for each sample, the specific heat capacity of water ( ) is 4.18J/g/oC, and the mass of the 100ml of water is 100g. The number of moles (n) can be found using .

- Ex. Ethanol Average Enthalpy Calculation = 139.3 kJ/mol Since this is a combustion reaction, is negative and therefore = -139.3 kJ/mol

Graph 1: The Molar Mass graphed against the experimental values for