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Run away exotherms

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Run away exotherms Introduction Every chemical reaction is associated by an enthalpy (energy) change. It is perceived as heat changes. Therefore, we can estimate the amount of energy that's been released. The value can be positive or negative depend if the reaction is exothermic or endothermic. The enthalpy change is represented by the symbol ?Hc. An exothermic reaction consists of releasing heat energy; this means the heat energy is lost to the surroundings. The enthalpy change value for exothermic reaction would always appear as negative. Inversely, an endothermic reaction takes in the energy from the surrounding. If there is no energy provided from the surrounding, the reaction would not occur. The enthalpy change value for endothermic reaction would always appear as positive. Aim: Find and compare the enthalpy change of two alcohols * PROPAN (I) OL C3H8O * PENTAN (I) OL C5H12O Prediction: The longer the molecule the bigger the value of enthalpy change The Technique: Measuring enthalpy changes by combustion The technique of this experiment is Calorimetry. It is used to find the enthalpy changes for a reaction taking place in solution. ...read more.


Conduction, convection and radiation: Conduction: Conduction occurs through the collisions between atoms and molecules in a substance. It is the transfer and distribution of heat energy from atom to atom within a substance. Conduction is most effective in solids. It can also occur in fluids. Radiation: Radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object. Convection: Convection is the flow of heat through a movement of air from a hot region to a cool region. As the air gets heated, the molecules spread out, therefore causes the region to become less dense than the surrounding. The movement of hot air will than into a cooler region is then said to transfer heat by convection. This is called the convection current. Calculation Energy gained can be calculated by the following formula: Heat energy = mass of substance x specific heat capacity x temperature change This calculation needs to be done for both the water and the metal container. The total is assumed to be equal to the energy released by the burning fuel. In practice, a large, but unknown, proportion of this energy is lost to the atmosphere. ...read more.


M = molar mass (in g mol-1) of the compound burned Primary Alcohols Methanol CH3OH 32 -726 Ethanol CH3CH2OH 46 -1367 Propan-1-ol C2H5CH2OH 60 -2021 Pentan-1-ol C4H9CH2OH 88 -3329 Hexan-1-ol C5H11CH2OH 102 -3984 Heptan-1-ol C6H13CH2OH 116 -4638 Octan-1-ol C7H15CH2OH 130 -5294 Above is a result table of how the final result should turn out Evaluation In this experiment there were many potential errors that could have affected the result. Theses included the accuracy of the measuring instruments such as the thermometer and the weighing machine. The result also could not be carried out under perfect lab conditions so the results will be inaccurate this is why in the equation I could not use ?H? c because I could not replicate these conditions. The hexan-1-ol results doesn't conform to the rest of the results this may have been because I measured the values wrong i.e. human error or it could have been that the result variables I mentioned first effected it. The results may also have been affected by energy that was wasted in the reaction because no experiment is 100% energy efficient. The energy would have been wasted in light from the flame and in a small amount of sound energy. ...read more.

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