Variables:
Independent variables:
Dependent variables:
- Change in temperature of water
- Amount of heat energy given out
- Change in mass of alcohol
Controlled variables:
- Volume of water used
- Distance between beaker and flame
- Amount of time the spirit lamp burns for
Materials:
- Measuring cylinder
- Water
- Spirit lamp
- Methanol
- Ethanol
- Butanol
- Glass beaker
- Thermometer
- Retort Stand
- Electronic balance
Method:
-
Measure 30cm3 using a measuring cylinder.
- Pour the water into a glass beaker and clamp it tightly to a retort stand.
- Measure the initial mass of the spirit lamp with the lid on using the electronic balance.
- Place the spirit lamp under the glass beaker.
- Measure the initial temperature of the water.
- Ignite the spirit lamp, allowing it to heat the water.
- Gently stir the water and record the temperature after every 10 second interval.
- Turn off the flame after 1 minute.
- Measure the final mass of the spirit lamp.
- Repeat the above steps 3 times for accuracy.
- Use another spirit lamp with a different alcohol and repeat the above steps.
Data Collection:
Data Processing and Presentation:
In order to calculate the energy released we use the following formula:
Energy = Mass of water (kg) × Specific heat capacity of water (J/Kg/°C) × Change in temperature (°C)
For example in the first experiment
Energy = 0.03 × 4200 × 22 = 2772 kJ
To find the mass per gram, divide the energy released by 1000.
To find the energy released per mole, divide the energy released by the number of moles.
The following shows a comparison of the averages for the 3 alcohols:
The data in the tables above can also be represented graphically as follows:
From the above graphs and tables it is clearly evident that butanol releases the most energy of the three types of alcohols. It is also evident that it produces the largest increase in temperature of the water. It releases more total energy in kJ and also more energy per gram and energy per mole.
Conclusion:
Butanol releases the most energy when compared to methanol and butanol. Butanol releases 4494 kJ of energy compared to 2646kJ released by methanol and 3066kJ released by ethanol. It is also superior to the methanol and alcohol in terms of the energy released per gram. It releases 4.49 kJ/g as compared to 2.65kJ/g released by methanol and 3.07 kJ/g released by ethanol. Butanol also releases more energy per mole when compared to methanol and ethanol. Butanol releases 344288 kJ/mol as compared to 173875 kJ/mol released by methanol and 249515 kJ/mol released by ethanol. This is as a result of butanol having more bonds that are broken and formed as compared to the other two types of alcohols. Hence its enthalpy of combustion is higher than methanol and ethanol, resulting into more energy being released during combustion.
Evaluation:
There were a few errors that could be avoided next time. All of the heat was not received by the beaker. Some of it was lost to the environment. In order to avoid this, there should be proper insulation so that all the heat is received by the beaker or there could be the usage of a calorimeter. Heat was also lost from the edges of the beaker, therefore a beaker that is a better conductor of heat should be used to minimize this effect. Sometimes there was some incomplete combustion and the flame was yellow and not blue because of the lack of oxygen. To avoid this, we should make sure that there is a proper supply of oxygen in the room with proper ventilation.
