You are required to design an experiment to test Hess's law using the combustion of ethanol. Write a brief design for this experiment.
What I wrote as my answer:
Hess’ Law: is the algebraic addition of chemical equations yields a net equation whose enthalpy of reaction is the algebraic sum of the individual enthalpies of reaction: ∆H net =[sum]∆H
The following experiment is a test of Hess’s law using combustion of Ethanol.
To test this and the acceptability of Hess’s law, the molar enthalpy of combustion of Ethanol is determined calorimetrically.
You did not write an experimental design.
I apologize for not including the experimental design in my previous response. Here is a brief design for an experiment to test Hess's Law using the combustion of ethanol:
1. Materials and Equipment:
- Ethanol (99% purity)
- Calorimeter
- Thermometer
- Measuring cylinder or pipette
- Bunsen burner or alcohol lamp
- Safety equipment (gloves, goggles, lab coat)
2. Procedure:
a. Measure and record the initial mass of the ethanol to be burned (Methanol A).
b. Fill the calorimeter partially with a known volume of water.
c. Measure and record the initial temperature of the water in the calorimeter.
d. Ignite the Bunsen burner or alcohol lamp.
e. Place the ethanol sample (Methanol A) on a heat-resistant surface, such as a wire gauze, and burn it completely using the Bunsen burner or alcohol lamp.
f. Allow the heat produced by the combustion of ethanol to enter the calorimeter, resulting in an increase in the temperature of the water.
g. Stir the water in the calorimeter gently to ensure even heat distribution.
h. Continue stirring until the temperature of the water stabilizes.
i. Measure and record the final temperature of the water in the calorimeter.
j. Repeat Steps a to i for a different sample of ethanol (Methanol B). This time, use a different initial mass of ethanol and a different volume of water in the calorimeter.
k. Perform Steps a to j for a third sample of ethanol (Methanol C), again with different values for the mass of ethanol and volume of water.
l. Calculate the heat absorbed by water in each experiment using the heat capacity of water and the change in temperature (∆T).
m. Use the equation Q = mc∆T, where Q is the heat absorbed, m is the mass of water, c is the specific heat capacity of water (4.18 J/g°C), and ∆T is the change in temperature.
n. Calculate the molar enthalpy of combustion for each ethanol sample using the equation:
∆H = Q / n
where n is the number of moles of ethanol burned.
3. Data Analysis:
a. Calculate the molar enthalpy of combustion for each sample of ethanol.
b. Compare the values obtained in step (a) and check if they are consistent with Hess's Law.
c. If the values are consistent, this confirms the validity of Hess's Law.
Note: This is a simplified experimental design. Additional procedural steps, safety precautions, and calculations may be required based on your specific laboratory guidelines and equipment availability.