A Lab experiment on how to determine the enthalpy change of the decomposition of Calcium Carbonate

The Enthalpy Change of the Decomposition of Calcium Carbonate

_INTRODUCTION_

RESEARCH QUESTION:

What is the enthalpy change of the decomposition of calcium carbonate?

BACKGROUND:

Enthalpy in chemistry can be thought of as the energy contained within the bonds, or the internal energy, but it is not heat and you can only measure changes in it. When bond bonds break in the reactants energy is given off, when bonds form, energy is absorbed. If the energy absorbed is less than the energy released, then the reaction is exothermic and the products are more stable than the reactants and vice versa. But, the enthalpy, or change in energy, of some reactions are too difficult to carry out in a standard laboratory due to toxins released or conditions that cannot be met in simple laboratory. Thus, that's where Hess's Law comes in as it states that if you go from the reactants to the products in one reaction or many intermediate steps, the _overall energy change is still the same_.

In this experiment, Hess's law will be utilized to calculate the decomposition of Calcium carbonate. Calcium carbonate is a fairly stable compound, thus, it must mean that more energy goes into this reaction than out to produce the desired results.

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

It is the enthalpy change of this reaction that this experiment was designed to find. Of course, another route must be used to achieve this, so HCl is added to CaCO3 and to CaO, and then, through some calculations and the equation

= M * C *

can the enthalpy of the decomposition of calcium carbonate be found.

CaCO3 + 2HCl ( CaCl2 + CO2 + H2O

CaO + 2HCL( CaCl2 + H2O

These two reactions will be done in a polystyrene beaker so no heat is released. But for the second reaction above, the opposite of the value obtained for the

must be added to the

of the first reaction because that is what will give the

of the decomposition of calcium carbonate as can be seen below.

So,

+ -

= the enthalpy of decomposition of CaCO3.

HYPOTHESIS:

If the enthalpy of the decomposition reaction of CaCO3 is measured, then a positive value for the enthalpy will be obtained

VARIABLES

_Independent Variables:_

The Molarity of the Acid used

The type and amount of the elements used

_Dependent Variables:_

The enthalpy of decomposition of CaCO3

_Control of Variables:_

The carefully performed reactions are done under certain conditions and in an enclosed container to ensure the most accurate results

_MATERIALS AND METHOD_

MATERIALS

Polystyrene Beaker with lid Thermometer (up to 100ºC)

100 ml of '2M' HCL CaCO

CaCO3 Balance

Graduated Cylinder

PROCEDURE

:

Weigh out 5 grams of CaCO3

In the polystyrene beaker, pour 50ml of the HCl

Then, very quickly, put the calcium carbonate in, put the thermometer in and close the lid

Begin to stir and record the initial and final temperatures

Repeat above steps 1 through 5 except use 2.8 grams of CaO instead of the CaCO3

_DATA COLLECTION AND EVALUATION_

TABLE 1:

Mass of calcium carbonate (CaCO3) used

5.0g

Temperature of acid initially

Temperature of acid after mixing

Temperature change during reaction

TABLE 2:

Mass of calcium oxide (CaO) used

2.8g

Temperature of acid initially

Temperature of acid after mixing

Temperature change during reaction

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_1205270462.UNKNOWN

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