Miss Case

Introduction

A large proportion of chemical reactions undergo exothermic or endothermic reactions.

In an exothermic reaction heat energy is released from the reacting chemicals (the system) to the surroundings. This happens because the products have a decreased internal energy in comparison to the combined energies of the reactants.

In contrast, an endothermic reaction results in heat energy being absorbed by the system from the surroundings. This is because the products have a greater internal energy than the combined reactants (Baxter and Heeley, 2008).

The diagrams below show a change in the internal energy of a system during an exothermic reaction and an endothermic reaction.

An experiment has been carried out to determine if the reaction of copper sulphate and zinc is an exothermic reaction or an endothermic reaction.

Method

Firstly, in accordance with health and safety a lab coat, safety glasses and gloves (personal protective equipment) were worn. This prevented exposure of the skin and eyes to the chemical compound, copper sulphate: which is toxic to a human if swallowed, inhaled or absorbed through the skin via direct contact.

25 cm3 copper sulphate solution was poured into a clean, dry graduated cylinder, taking care to measure as accurately as possible. The lid of the copper sulphate container was replaced so the container was securely sealed. A polystyrene cup was placed into a glass beaker which acted as an insulator, helping maintain the experiment at room temperature.

The measured copper sulphate solution was then added into to a polystyrene cup. A thermometer was immediately placed into the system to record the initial temperature, minimising associated uncertainties. A record of the value for temperature was made in a results table, in degrees Celsius.

Then, using the top-pan balance, 3.25 g of zinc powder was carefully placed into a clean, dry weighing boat. After this, the zinc powder was added to the copper sulphate solution, starting the stop-clock immediately to reduce the uncertainty of the subsequent values recorded. The system was stirred continuously using