# Enthalpy Change

Skill P – Planning

• The aim of this practical experiment is to determine the enthalpy change for this reaction by an indirect method based on Hess’s Law. Both Calcium Oxide and Calcium Carbonate react readily with 2 mol dm Hydrochloric Acid solutions. The temperature changes during these reactions can be measured and the enthalpy changes calculated.

• Chemicals and apparatus:
• 250 cm measuring cylinder
• 2 mol dm Hydrochloric Acid
• 250 cm beaker
• 0 - 10 0° C  thermometer (graduations to 1° C  )
• 2.4 – 2.6 g of Calcium Carbonate
• 1.3 – 1.5 g of Calcium Oxide

• Procedure
1. Weigh out a weighing bottle containing between 2.4 and 2.6 g of Calcium Carbonate
2. Weigh out a weighing bottle containing between 1.3 – 1.5 g of Calcium Oxide
3. Using the measuring cylinder provided place 50 cm3 of 2 mol dm3 hydrochloric acid (an excess) into a 250 cm3 glass beaker.
4. Measure the temperature of the acid using the thermometer provided.
5. Add the calcium carbonate/ calcium oxide to the acid.
6. Take the temperature again when the reaction is complete.
7. Weigh the weighing bottle.

• Before we begin the experiment we will make sure that the desk, all the instruments and apparatus are clean. We will follow the method carefully in order to get precise and reliable results.

• We will also record all the results in the table provided, in order to analyse and calculate, when the experiment will be completed.

Skill A – Analysing Evidence and Drawing Conclusions

Results:

• 50 cm of 2 mol dmHCl
• Heat capacity of HCl (aq) = 4.2 J gK {Specific heat capacity is the measure of the heat energy required to raise the temperature of a specific quantity of a substance (thus, the name “specific” heat) by certain amount, usually one Kelvin. The modern SI units for measuring specific heat capacity are the joule per gram per Kelvin (J g–1 K–1)}
• Density of HCl (aq) = 1.0 g cm

The aim of this experiment is to determine the Enthalpy Change of a Reaction.

The enthalpy change of this reaction is difficult to measure directly but can be found by an indirect method based on Hess’ law. Hess’s Law of constant heat summation shows that whatever the route from given reactants to products, the overall energy change must be the same.

In this approach, calcium carbonate and calcium oxide are reacted separately with hydrochloric acid and the enthalpy changes of the two reactions are measured. These enthalpy changes are then used to calculate the enthalpy change for ...