Enviro: Energy and Kj Essay

Submitted By bgkartha
Words: 502
Pages: 3

Total amount of chemical energy stored inside candle wax through a heat of combustion
Aim- the aim of this experiment was to find out the total chemical energy that was stored within the paraffin wax and how much of this energy is transferred into the water.
Mass of candle (g) Temperature of water ( 0C)
Initial 12.6 22
Final 11.8 42
Deviation 0.8 20

Heat capacity of water = 4.184J per mL per 0C
Total energy absorbed by water (J) = 4.184 x volume of water x temperature deviation from initial temperature
Total energy (J) = 4.184J/mL/C0 x 200mL x 200C
Total energy = 16,736 J = 16,736 x 1/1000 = 16.736 kJ
Heat of combustion (kJ/g) = energy released (kJ)/ initial mass of candle (g) – final mass of candle (g)
Heat of combustion (kJ)/g) = 16.736 kJ / 12.6 g – 11.8 g
Heat of combustion (kJ)/g) = 16.736 kJ / 0.8 g = 20.92 kJ/g
When candle wax is heated the potential chemical energy stored in the candle wax is converted into heat, sound, kinetic and light energy. The following are the energy transformation taking place:
1. As this is a combustion reaction there will be heat released therefore there will a lot of thermal energy produced
2. Some water molecules that has absorbed the heat energy from the reaction will evaporate and causes heat energy to be converted into kinetic energy.
3. A small proportion of energy is converted into light energy as a flame
4. Sound energy which is when the candle sometimes produces a crackling noise although this is trivial.

Efficiency (%) = (useful energy output (kJ/g) / total energy output (kJ/g)) x 100
Efficiency of candle = (20.92 / 42) x 100 = 49.81% rounded to 2 decimal places
Therefore 50.19% of energy from the candle wax has been wasted in the process as shown above and not absorbed by the water.
As mentioned before heat from the flame radiates in all direction not just towards the water so huge quantities of…