To determine which alkanols has higher heat combustion Hypothesis: The alkanols with the longer carbon chain will a higher heat combustion Background Information: Heat combustion can be calculated by using various formulas. By using ? H= -mc? T, we can gather the amount of heat released. Since the experiment is exothermic, ? H will have a negative value. By dividing the total amount by 1000, the units changes into KJ.
Divide the total KJ of heat by the amount of fuel used(in grams) which gives the amount of kilo jewels per gram. By multiplying the total value by the molar mass of the alkanols will give the total KJ/mol. Method: 1. Use a clamp to connect a metal cup to a retort stand 2. Measure the initial weight of the of the alkanols 3. Add exactly 100 ml of water into the cup 4.
Place the alkanols fuel source under the metal cup 5. Take the initial temperature of the water 6. Light the fuel source to heat the cup of water . When the temperature of the water increases by exactly 20 ? C, blow out the flame 8. Measure the new weight of the fuel source 9. Record the result 10. Repeat for the other alkanols Results: Alkanols used| Fuel used (grams)| Kilo jewels per gram (KJ/g)| Kilo jewels per mole (KJ/mol)| Class average (KJ/g)| Class average (KJ/mol) | Methanol| 1. 02| -8. 2| -262. 7| -8. 4| -291| Ethanol| 0. 77| -10| -435| -12. 1| -536| Propanol| 0. 78| -10. 7| -644| -18. 85| -883. 2|
The molar heat combustion increases with carbon chain lengths as the alkanols contains hydrogen bonding and because of more carbons, this results in increased dispersion forces along the chain, thus the activation energy is higher and has a higher molar heat combustion. Discussion: The experiment results fell a little out of range of the class average. The reliability of the experiment was high as most groups in the class results were consistent. The accuracy could have been improved by using digital thermometers and more accurate measuring cylinders and scales.
Some or very little heat was lost from the metal cup due to surrounding environment. Also the position of the fuels source under the metal cup can affect the accuracy. As the condition of the experiments was kept the same for the groups, the experiment had a high validity. Safety Wear safety glasses due to ignition of chemicals Tie hair back due to fire hazards Environmental As alkanols are hydrocarbons, they are organic thus proper disposable needs to take place. Conclusion: In conclusion, the hypothesis of alkanols with longer carbon chains will have a higher heat combustion was correct.