• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4

# The enthalpies of combustion are different depending on the number of carbons and hydrogens in each substance. For example, the enthalpy combustion for methane is -890 kJ mol-1, however the enthalpy change of combustion for ethane or propane will be grea

Extracts from this document...

Introduction

Introduction on enthalpy of combustion Standard enthalpy change of combustion is the energy change that occurs when 1 mol of fuel is completely burnt in oxygen under standard conditions. However, it is impossible for substances to be burnt under standard conditions. The enthalpies of combustion are different depending on the number of carbons and hydrogens in each substance. For example, the enthalpy combustion for methane is -890 kJ mol-1, however the enthalpy change of combustion for ethane or propane will be greater because more bonds are involved and therefore more bonds are broken and made. All combustion reactions are exothermic because energy is given out to make bonds. Figure 1: Exothermic reaction Before you start doing calculations for enthalpy change of combustion you firstly need to balance the equation. For example: Methane CH4 (g) + 2O2 (g) 2H2O (g) + CO2 (g) Also it is important to note when making a combustion reaction balanced equation that the state symbols for all the substances are gaseous even water. ...read more.

Middle

8. Weigh the alcohol and record the reading. Also record the reading of the temperature after it has increased. 9. Repeat steps 1-8 for all different alcohols. Results obtained from experiment Methanol Ethanol propan-1-ol Butan-1-ol Pentan-1-ol Enthalpy change of combustion (kJmol-1) 379.80 1071.23 1332.62 1715.82 2110.04 Enthalpy change of combustion = (1/moles of alcohol burned) x enthalpy released during the ex. True results of alcohols that should be obtained Methanol Ethanol propan-1-ol Butan-1-ol Pentan-1-ol Enthalpy change of combustion (kJmol-1) -890.30 1559.70 2219.70 2876.50 3509.10 From the results I obtained I can make a conclusion that the results were not very close to the true, this is because the experiment could not done under standard conditions like the other and therefore because of that some heat was lost to the surrounding. While I was carrying the experiment I realised that a black substance began to form underneath the colorimeter (container where the water was put in and heated up) ...read more.

Conclusion

propan-1-ol Butan-1-ol Pentan-1-ol Final mass of spirit burner / g 197.41 188.16 180.09 212.08 189.08 Percentage error / % 0.003 0.003 0.003 0.002 0.003 Looking at the results above for the percentage errors, I can conclude that the balance did not effect the results I obtained as it gave me a small percentage error that was less than 1%. This ensures me that the measurements of the spirit burners that I obtained using the weighing balance where very accurate. Procedural errors * A thermometer was placed on the colorimeter and when reached to 500c and recorded the highest temperature by siring until there was no increase in temperature. * Keep lid on spirit burner to endure the alcohol did not evaporate to obtain a accurate measurement of the mass of alcohol combusted. * Draft exclusion made using insulating tiles. This is so less heat and temperate near the spirit burner that is lighted is relatively kept constant and not effected by air coming from window or heat from radiator. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Physical Chemistry section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related AS and A Level Physical Chemistry essays

1. ## Determination of the enthalpy change of neutralization

The slope of the curve plotted by method 2 is smoother and more accurate than method 1 because temperature change is measured at a smaller interval. The concentration found is more accurate. However, Method 1 is more suitable in determining the enthalpy change of neutralization.

2. ## SIMPLE CALORIMETRY TO FIND THE ENTHALPY OF COMBUSTION OF ALCOHOLS

13.0? Initial Final Mass of Ethanol used Mass of the spirit burner with Ethanol: 159.352g 158.681g 0.671g Volume of water: 300mL Combustion of Propan-1-ol: Final Initial Temperature increase Temperature of water: 36.0? 23.0? 13.0? Initial Final Mass of Propan-1-ol used Mass of the spirit burner with Ethanol: 156.018g 155.366g

1. ## Investigating how concentration affects rate of reaction

I will elaborate on this and other problems in my evaluation section. Evaluation In general I think that my investigation went well. I succeeded in all of my initial aims and produced accurate, reliable results. I only encountered one real anomaly throughout the investigation process (highlighted in my conclusion).

2. ## Determination of the enthalpy change of combustion

Propan-1-ol has the highest enthalpy change. Methanol, ethanol and propan-1-ol are all alkanols which belong to the same homologous series. When the number of carbon atoms is increasing, it is difficult for the alcohols to undergo complete combustion as van der Waals' forces increases.

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to