Experiment 3 Molar heat of combustion of ethanol

Summary

In this educational video, students are guided through an experiment on the heats of combustion of various alcohols, focusing on ethanol. The presenter demonstrates the setup and methodology, detailing the importance of measuring initial and final temperatures, as well as the mass of the alcohol used. Key calculations are explained to determine the molar heat of combustion, highlighting discrepancies between experimental and theoretical values due to factors like incomplete combustion and heat loss. The video encourages students to compare results from different alcohols, fostering a deeper understanding of combustion chemistry.

Takeaways

• 🔬 The experiment aims to compare the molar heats of combustion for different alcohols, focusing on ethanol as a potential alternative fuel.
• ⚗️ Initial measurements include recording the mass of the spirit burner and measuring 100 mL of water for the reaction.
• 🌡️ The starting temperature of the water is recorded at 23°C, which is crucial for calculating the temperature change during the experiment.
• 🔥 Ethanol is ignited to heat the water, aiming for a temperature increase of approximately 20°C over about 2 minutes.
• 📈 The highest temperature observed was 48°C, indicating a significant increase due to the combustion of ethanol.
• ⚖️ The final mass of the spirit burner is measured after the reaction, with the mass change being essential for calculating the amount of ethanol combusted.
• 🧮 The energy transferred to the water is calculated using the formula ΔH = -CΔT, resulting in an energy transfer of 10,450 Joules.
• 📊 The molar heat of combustion is determined by relating the energy transferred to the mass of ethanol used, yielding an empirical value of approximately 286.55 kJ/mol.
• ❗ There is a notable difference between the experimental value and the theoretical value of 1367 kJ/mol, attributed to incomplete combustion and heat losses.
• 🔍 Understanding experimental errors and sources of discrepancy is crucial for improving future experiments on combustion.

Q & A

What is the main objective of the experiment described in the video?

The main objective is to compare the molar heats of combustion of different alcohols, focusing on ethanol as an alternative fuel.

What materials are required for conducting the experiment?

Materials required include a spirit burner filled with ethanol, a balance for measuring mass, a beaker containing 100 mL of water, and a thermometer for measuring temperature.

How is the initial temperature of the water measured?

The initial temperature of the water is measured using a thermometer placed in the beaker before heating.

What is the target temperature increase for the water during the experiment?

The target temperature increase for the water is approximately 20°C.

What calculations are involved in determining the heat energy transferred to the water?

The heat energy transferred is calculated using the formula ΔH = -m × c × ΔT, where 'm' is the mass of water, 'c' is the specific heat capacity, and 'ΔT' is the change in temperature.

What is the specific heat capacity of water used in the calculations?

The specific heat capacity of water used in the calculations is 4.18 J/g°C.

How is the molar heat of combustion for ethanol calculated in the experiment?

The molar heat of combustion is calculated by finding the energy transferred to the water and using the mass of ethanol burned to establish a ratio, ultimately resulting in kilojoules per mole.

What discrepancy is noted between the experimental and theoretical values of ethanol's combustion?

The experimental value is significantly lower than the theoretical value, indicating that the combustion may not be complete and that heat is lost to the environment.

What factors contribute to the difference between empirical and theoretical values in this experiment?

Factors include incomplete combustion, heat loss to air and equipment, and potential delays in measurement affecting heat retention.

Why is it important to conduct the experiment with multiple alcohols?

Conducting the experiment with multiple alcohols allows for comparative analysis and helps in graphing trends related to combustion energy as the carbon chain length increases.