# Thermal Decomposition of Calcium Carbonate

Chemistry Coursework – Assessed Practical

Introduction

Calcium Carbonate, CaCO3 decomposes with heat, to produce Calcium Oxide, CaO and Carbon Dioxide, CO2.

CaCO3(s)                                                             CaO(s) + CO2(g)

The object of this practical exercise is to determine the enthalpy change for this reaction by an indirect method based on Hess’ Law.

Results Table

Experiment 1:

Experiment 2:

Calculating the Enthalpy Change

Experiment 1: Calculating the    H1 for the reaction between CaCO3 and HCl

Using the formula:

Density = Mass

Volume   ,

We can work out the mass of liquid (HCl)

Mass = Density x volume

= 2.0 x 0.05

= 0.1 grams

Using the calculated mass, we can work out the total energy transfer using the formula:

Energy Transfer = Mass of Liquid x specific heat capacity x change in temperature

= 0.1 x 4.2 x (24-22)

= - 0.84 J

From the results table, we can see that the temperature increased from 22oC to 24oC, so we can deduce that the reaction was EXOTHERMIC.

To work out      H1 we need to find the energy transfer per 1 mole of calcium carbonate, but first I need to calculate the number of moles in calcium carbonate:

Number of moles =                Mass

Mr

= 2.39

100.1

= 0.02387612388 moles

= 0.024 moles (3 d.p.)

Therefore,

H1 = - 0.84

0.024

= -35 J mol-1

Experiment 2: Calculating the    H2 for the reaction between CaO and HCl.

Using the formula:

Density = Mass

Volume   ,

We can work out the mass of liquid (HCl)

Mass = Density x volume

= 2.0 x ...