Go Green :D: Effectiveness and Efficiency of Fuels

In Lesson 6, we tested the effectiveness of fuels and measured the efficiency of fuels by combusting some fuels. The following chemicals and apparatus were used:

Methanol

Cyclohexane

Biodiesel made in the previous lesson

Cotton wool

Tweezers

Bunsen burner

Stopwatch

Metal Tongs

2 x Thermometers

2 x Evaporating dish

2 x Wire mesh

2 x 10ml measuring cylinder

1 x 100ml measuring cylinder

250ml beaker

Mass balance

Scientific Concepts/ Processes behind the efficiency of fuels

In this experiment, we aimed to test the efficiency of methanol, cyclohexane and various groups' homemade (or labmade) biodiesels. We ignited the flammable fuels and allowed it to heat up a fixed small volume of water (10ml) for a fixed amount of time (2 minutes). The initial and final temperature of the water was taken down in order to calculate the enthalpy change of the combustion reaction.

Fuel efficiency is using the least amount of fuel to travel the greatest distance. This is important as it reduces our dependency on oil/ fossil fuels. At the same time, a more efficient fuel translates to less combustion of fuels and hence less carbon dioxide released during the combustion reaction. It also saves money and increases energy sustainability, which is to use the fuel which can produce the most energy.

However, contrary to what we may think, our common fossil fuel engines are not very efficient! In fact, only 15% of energy from fuel moves the vehicles or runs accessories such as the radio in the car. The rest of the energy is lost to heat and exhaust. Hence, it is even more important that we aim to use the most efficient fuel such that precious energy is not wasted.

Results obtained and Calculations of Enthalpy Change

Type of fuel	Methanol	Cyclohexane	Biodiesel 1 (corn oil)	Biodiesel 2 (corn oil)	Biodiesel 3 (corn oil)	Biodiesel 4 (corn oil)	Biodiesel 5 (vegetable oil)
Initial temperature of water/^oC	31.0	31.0	All the biodiesels made by us failed to combust as there was too much water content in the biodiesel – thus, we should have carried out more separation using the separation funnel to ensure the fuel is pure.
Final temperature of water/^oC	100.0	75.0

In order to calculate enthalpy change, the following steps were necessary:

1. Calculate heat absorbed by the water using mcΔT (m= mass, c= specific heat capacity of water, ΔT= change in temperature).

2. Calculate the moles of the fuel burnt using mass/Mr.

3. Calculate enthalpy change using heat energy/moles.

Cyclohexane

Heat absorbed by water (Q) = (779 x 10 x 10^-6)(4.181)(75.0 – 31.0) = 1.4331 kJ (5sf)

Moles of cyclohexane burnt = 0.010 ÷ (12.0 x 6 + 1.0 x 12) = 0.00011905 mol (5sf)

Enthalpy change = 1.4331 ÷ 0.00011905 = 12000 kJ mol^-1(3sf)

Methanol

Heat absorbed by water (Q) = (791.30 x 10 x 10^-6)(4.181)(100.0 – 31.0) = 2.2828 kJ (5sf)

Moles of methanol burnt = 0.010 ÷ (12.0 + 1.0 x 4 + 16.0) = 0.0003125 mol

Enthalpy change = 2.2828 ÷ 0.0003125 = 7300 kJ mol^-1(3sf)

From the above, we can conclude that cyclohexane is the more efficient fuel as it produced the most amount of energy for every mole of the fuel. Hence, it would be better for us to use cyclohexane in order to reduce our carbon footprint as well as save money! :D

However, there were some limitations to this experiment. It was hard to control the ignited flame from the fuel. Hence, in order to minimize error, we made sure that the tip of the flame touched the beaker of water for every ignited fuel. There is also heat loss to the surroundings (thermometer, air etc) during the heating of the beaker of water, so we are unable to account for this loss of heat energy.

Pictures!