To Determine the Enthalpy of H2O2 Decomposition in Aqueous Solution

Presented by :-

Rajan Baa Soumyadipa DasAbison Scaria

What is calorimetry?

The process of measuring the heat of chemical reactions or physical reactions as well as heat capacity.

Differential scanning calorimeter

Bomb calorimeter

Isothermal titration calorimeter

And that’s where we need a calorimeter.

Some of them are

We would need some pre requisite knowledge of a few terms.

Enthalpy

Adiabatic process

Heat capacity

q= Cp T

H= Cp T

H2O2 (aq) H2O (l) + ½ O2 (g)

Isobaric calorimeter with stirrer and precision thermometer100 mL volumetric flask250 mL measuring cylinder10 mL pipetteChronometerPipette fillerWash bottleSpatula

Equipments:

Chemicals:Sodium nitrite NaNO2Sulphamic acid NH2SO3H11.2 volume strength of H2O2

Manganese dioxide MnO2

Experiment

Calibration: Measurement of the Heat Capacity of the Calorimeter

Measurement of the Enthalpy of Decomposition of Hydrogen Peroxide

Calibration: Measurement of the Heat Capacity of the Calorimeter

NH2SO3H (aq) + NaNO2 (aq) N2 (g) + H2O (l) + NaHSO4 (aq)

For this reaction at 25 °C, rHm = –420.5 kJ mol–1

1.

Accurately weigh out 11.30 g of NaNO2, dissolve in distilled water and make up to 100 mL in a 100 mL volumetric flask.

2. Transfer 600 mL of distilled water to the calorimeter

Add 5 g of sulphamic acid and turn on the stirrer!

Switch on the stirrer and allow ten minutes for the sulphamic acid to dissolve completely and for an equilibrium rate of temperature rise to be established. Start the chronometer and take temperature readings at one minute intervals for five minutes to define the slope of the pre-reaction period.

On five minutes, pipette 10 mL of the NaNO2 solution into the calorimeter through the open glass tube in the lid.

The temperature rises rapidly. By six minutes the actual reaction should be complete. Continue taking readings at one minute intervals from six minutes to ten minutes to establish the slope of the post-reaction period.

H = Cp T

Known from literature

From the graph of temp vs time.

Determination of Enthalpy of decomposition of H2O2

H2O2 (aq) H2O (l) + ½ O2 (g)

H2O2

Transfer 600 mL of distilled water to the calorimeter and put the lid on. Attach the stirrer cable. Pipette 10 mL of the hydrogen peroxide solution into the calorimeter.

Switch on the stirrer and allow ten minutes for an equilibrium rate of temperature rise to be established.

Time

tem

pera

ture

Weigh out roughly 6 g of manganese dioxide

On five minutes, add the manganese dioxide through the open glass tube in the lid to catalyse the decomposition. The temperature rises rapidly. By six minutes the actual reaction should be complete.

Time

tem

pera

ture

MnO2

Continue taking readings at one minute intervals from six minutes to ten minutes to establish the slope of the post-reaction period.

tem

pera

ture

time

time

Tf

Ti

tem

pera

ture

T

the concentration of H2O2 was determined by titration against standard potassium permanganate solution

Given this concentration, we can calculate the quantity of H2O2 added to the calorimeter in moles. From the number of moles of H2O2 added to the calorimeter, rHm was found out to be -96 kJ /mole.

References:article from manchester university presswww.chem.tamu.edu

Thank you...