Experiment 3 Molar heat of combustion of ethanol

Introduction

This tutorial provides a step-by-step guide on conducting an experiment to determine the molar heat of combustion of ethanol. Understanding this concept is essential in chemistry, especially in the study of thermodynamics and energy changes during chemical reactions.

Step 1: Gather Materials

To perform the experiment, you will need the following materials:

• Ethanol (C2H5OH)
• A calorimeter or a simple setup using a metal can
• A thermometer
• A balance (for measuring mass)
• A Bunsen burner or another heat source
• A measuring cylinder
• Water
• Safety equipment (gloves, goggles, lab coat)

Practical Advice

• Ensure all your materials are clean and dry to avoid contamination.
• Prepare your workspace with all necessary safety equipment in place.

Step 2: Set Up the Calorimeter

1. Measure Water: Use the measuring cylinder to measure a specific volume of water (e.g., 100 mL) and pour it into the calorimeter.
2. Record Initial Temperature: Insert the thermometer into the water and record the initial temperature (T_initial) of the water.
3. Prepare the Ethanol Burner: Weigh the empty burner to get its mass. Then fill it with a known amount of ethanol and weigh it again to determine the mass of ethanol used for combustion.

Practical Advice

• Place the calorimeter on a stable surface to avoid spills.
• Make sure the thermometer does not touch the sides or bottom of the calorimeter for accurate readings.

Step 3: Conduct the Combustion

1. Ignite the Ethanol: Carefully ignite the ethanol burner and allow it to heat the water.
2. Stir the Water: Gently stir the water to ensure even heat distribution.
3. Monitor Temperature: Continuously monitor the water temperature until it reaches a stable maximum temperature (T_final). Record this temperature.

Common Pitfalls to Avoid

• Avoid direct contact with the flame and hot surfaces.
• Ensure the burner is placed directly beneath the calorimeter for efficient heat transfer.

Step 4: Calculate the Heat Released

1. Determine Temperature Change: Calculate the change in temperature using the formula: [ \Delta T = T_{final} - T_{initial} ]

2. Calculate Heat Absorbed: Use the formula for heat absorbed by the water: [ q = m \cdot c \cdot \Delta T ] Where:

   • ( m ) = mass of water (in grams, assuming 1 mL = 1 g)
   • ( c ) = specific heat capacity of water (4.18 J/g°C)

3. Calculate Molar Heat of Combustion: Determine the molar heat of combustion (ΔH_comb) using the heat released and the number of moles of ethanol combusted: [ \Delta H_{comb} = \frac{q}{n} ] Where ( n ) is the number of moles of ethanol used.

Practical Advice

• Be meticulous with your measurements to ensure accuracy.
• Convert the mass of ethanol to moles using its molar mass (46.07 g/mol).

Conclusion

In this experiment, you have learned how to determine the molar heat of combustion of ethanol through careful measurement and calculation. Key takeaways include the importance of accurate temperature readings and mass measurements. For further exploration, consider conducting similar experiments with different alcohols to compare their heats of combustion. Always remember to follow safety protocols when handling chemicals and open flames.