Energy from Fuels (WJEC GCSE Chemistry)

Specified Practical: Determining Energy Released from Fuels

Introduction 

• When a fuel, such as alcohol, burns it reacts with oxygen to release energy 

• Carbon dioxide and water are also produced 

• The general equation for the combustion/burning of an alcohol is:

alcohol  +  oxygen →  carbon dioxide  +  water

• Different alcohols will release different amounts of energy when they burn 

• This investigation will determine which fuel releases the most energy per gram when it burns in oxygen

Apparatus

• Clamp stand

• Clamp and boss

• 250 cm³ conical flask

• 100 cm³ measuring cylinder

• Thermometer

• Electronic balance ± 0.01g

• Spirit burners containing:

  • Methanol

  • Ethanol

  • Propanol

  • Butanol

Diagram

How to set up your apparatus 

Method

1. Use a measuring cylinder to measure 100 cm³ of water into a conical flask

2. Clamp the conical flask to the clamp stand at a suitable height so the spirit burner can be placed below 

3. Record the temperature of the water using the thermometer 

4. Record the mass of the spirit burner (including lid) using the balance 

5. Place the spirit burner under the conical flask and light it

6. Allow the burner to heat the water until the temperature increases by approximately 40 ^oC

7. Record the temperature of the water

8. Extinguish the flame and record the mass of the spirit burner 

9. Repeat steps 1-8 with the other alcohols 

Practical Tip 

• Make sure the thermometer does not touch the bottom of the conical flask or the temperature will be inaccurate

• Alcohols are highly flammable so make sure this experiment is conducted in a well ventilated lab and away from other flames

Analysis of Results 

• You will be required to create a suitable results table for this experiment:

Evaluation 

• Calculate the temperature rise for each fuel

• Calculate the mass of each alcohol burnt

• Calculate the energy released for each alcohol using:

Conclusion 

• Describe what the results show, for example:

  • Which fuel releases the most energy per gram?

  • Which fuel releases the least energy per gram?

• Describe any patterns in the results

  • Is there a relationship between the size of the molecule and the amount of energy released per gram  

  • Remember, the size of the alcohols beginning with the smallest is:

    • methanol < ethanol < propanol < butanol